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Shuffling Quantum GIS into the Open Source GIS Stack

1. Quantum GIS FOSS4G2007 35 5 3 TESTING THE MAP FILE CHAPTER 5 MAKING MAPSERVER MAP FILES If you plan to use the map file to serve WMS requests you probably don t have to tweak anything If you plan to use it with a mapping template or a custom interface you may have a bit of manual work to do To see how easy it is to go from QGIS to serving maps on the web take a look at Christopher Schmidt s 5 minute flash video http openlayers org presentations mappingyourdata Quantum GIS FOSS4G2007 36 Chapter 6 Consuming WMS and WFS Data QGIS supports WMS and WFS as data sources The support for WES is preliminary at this time WMS support is native WFS is implemented using a plugin 6 1 Using WMS Data To add WMS data to your map click on the tool to bring up the dialog or you can choose Add WMS Layer from the Layer menu The first time you use the WMS feature there are no servers defined Fortunately you can add some servers to play with by clicking the f Add default servers button This will add at least three WMS servers for you to use including the NASA JPL WMS server Exercise 14 Loading a WMS Layer To add a layer from the server Click on the tool If you haven t already done it click on the Add default servers button Select NASA JPL from the drop down list Click The Layers list will be populated with the available layers Click on layer id 1 to ex
2. Quantum GIS FOSS4G2007 13 2 4 SYMBOLIZING YOUR DATA CHAPTER 2 GETTING STARTED Symbology Tab We ve discussed the Symbology tab in the previous section In addition to choosing a renderer the tab allows you to set the transparency for the layer When using a renderer on this dialog you can change the colors for a given class or property by clicking on the associated color box to popup the color selector The best way to get acquainted with the renderers and their capabilities is to experiment with them General Tab The General tab is essentially like that of the raster dialog It allows you to change the display name set scale dependent rendering options and view or change the projection The button allows you to create a subset of the features in the layer but this only works for PostGIS layers Metadata Tab The Metadata tab contains information about the layer including specifics about the type and location number of features feature type and the editing capabilities The projection and attribute fields and their data type are displayed on this tab This is a quick way to get information about the layer Labels Tab The Labels tab allows you to enable labeling features and control a number of options related to placement style and buffering Exercise 5 Labeling Cities Let s illustrate by labelling the cities on our map Zoom in a bit to your favorite continent Make the cities layer active Op
3. You can configure the connection to only look for layers in the geometry_columns table This will speed up the populating of the layer list but will miss layers that aren t in the geometry_columns table If you always create your PostGIS layers in a way that creates an entry in the geometry_columns table then it s safe to check this option The other option allows you to only search the public schema for spatial tables This also speeds up the populating of the layer list but is only helpful if you layers are always stored in the public schema 40 CHAPTER 7 VIEWING AND EDITING DATA IN POSTGIS 7 1 VIEWING DATA Our completed connection dialog is shown below Create a New PostGIS connection Connection Information Name Local Host localhost Database livecd Port 5432 Username qgisuser Password Save Password Jest Connect _ Only look in the geometry_columns table Only look in the public schema 7 1 2 Loading Data Let s use the new connection to load a layer Exercise 17 Loading the Cities Layer from PostGIS To load the cities layer from PostGIS 1 Choose your connection from the drop down box Click Choose the cities layer from the list Change the encoding if you need to Click Dor WwW NY Click on in the toolbar Once loaded the PostGIS layer behaves like any other vector layer 7 1 3 Creating Subsets When loading a
4. 0 Points L te 1_point E BY world_borders Areas 0_polygon islands S 1 polygon North 78 11 59 989014N i gy PERMANENT South 53 09 00 0054935 East 177 07 48 676758E West 165 16 12 015381W 3D no History COMMAND v in ogr o dsn home gsherman desktop_gis_data cities shp output cities min_area 0 0001 snap 1 GISDBASE home gsherman gsherman dapper grassd ata le LOCATION world_geo MAPSET gsherman USER gsherman DATE Sun Aug 26 As we work with GRASS maps a history is recorded You can see in our browser example the command used to create the cities layer from the original shapefile This is displayed in the right pane just below the extent information Using the browser gives you a quick overview of your maps and layers as well as some detailed information about the number of features and the history of the map The toolbar in the browser has a number of useful functions for working with and managing our maps layers You can add a layer to the map canvas copy a map rename a map delete a map set the current region to that of the selected map and refresh the browser tree The browser is a handy tool when working with and managing your GRASS data 8 6 Analysis Most people are aware that GRASS has some powerful features The QGIS GRASS plugin makes access to those features easier and also facilitates learning about what s going on behind the
5. 27 Remove the plugin menu item and icon 28 self iface removePluginMenu New PostGIS Layer self action 29 self iface removeToolBarlcon self action In lines 2 through 7 we import the libraries needed for the plugin This includes the PyQt libraries the QGIS core library and the Python PostgreSQL library psycopg Every Python script that uses the QGIS libraries and PyQt needs to import the QtCore and QtGui libraries as well as the QGIS core library This gives us access to the PyQt wrappers for our Qt objects like our input dialog and the QGIS core libraries We also need to import the resources py file we created with the icon definition In line 10 we declare the class NewLayer In the init method lines 12 through our class is initialized and passed the iface object from QGIS via the classFactory method in line 10 of _init_ py We store iface as a member variable so we can use it later In lines 16 through 24 we initialize the GUI elements for the plugin In Qt a QAction is used to create a user interface action that can be used to create both a menu and toolbar item In our plugin we use it for both In line 18 we create the action using our icon resource note Quantum GIS FOSS4G2007 55 45 9 5 CREATING THE PLUGIN CHAPTER 9 PYTHON PLUGINS the prefix we specified in resources qrc We also provide some text that will appear when it is used in a menu or during a mouseover and lastly we n
6. you can run the LiveCD on it assuming it s an i386 machine or you can use pre installed software you may have already We will be using the following applications QGIS 0 8 1 2 GRASS 6 2 or higher 3 PostgreSQL with PostGIS 4 QGIS 0 9 0 E 1 3 Data For the workshop we will be using a dataset found on the LiveCD If you wish to use your own laptop and software for the workshop you can install the data from one of several CDs we have available 1 4 Conventions In the text you will find several conventions to indicate certain items and actions 1 4 CONVENTIONS CHAPTER 1 INTRODUCTION e A button on a dialog e QInputDialog A class name e LENGTH A field in a layer or table e cities shp A file or directory name e Enter A key on the keyboard e getName A class method e File A Menu Item e localhost A server name e geometry_columns table in a database A Tool on the Toolbar e Text you type Text you type Quantum GIS FOSS4G2007 8 Chapter 2 Getting Started In this chapter we ll look at the basics of QGIS including viewing and symbolizing data as well as working with attributes and actions We ll be using the LiveCD if you want help installing QGIS see Appendix A for information specific to your platform 2 1 Using the LiveCD To use the LiveCD you must reboot The LiveCD is based on 1 Insert the LiveCD into the CD R
7. 26 26 28 28 29 30 31 32 32 E yee e eo eee o as aid ee ee O eos ee oh ne eee a A ph SMe ee hot GOO a eh ae Bee ena eS gree ee Senta e ee Sh os Re a ee a ee ee A Geek ee Gee ea nes Gee be BE ee ie eh eres Dee ed ee eh ts GLA Creatine a VIEW bee Ree we eg wc ee eee ewe Roe ee Boa bid dod Gh eae Boe dan ea eg ake ay eee eee Ge BS E de typ re nde We ge eats Mees an See BS erase ee ae N ee i RASS and Q 8 1 The GRASS Plugin oaaae 8 2 Creating a Location s soe he ouer Ro oe oe ee ee eR ee ee 9 39 Importing Data s os aoe Re ee eae Bo ee ee eed a Be A tie ee 8 3 1 Importing Vectors 2 20 0 0 0 8 3 2 Importing Rasters o o 00002 ee ee 8 4 Digitizing and Rd 8 5 Using the Browser e 8 6 Analysis 8 6 1 Creating a Buffer o e 8 6 2 Creating Contours e 8 6 3 Map Algebra e 8 7 Summary 9 Python Plugins 9 1 Setting up the Structule ee 9 2 Making the Plugin Recognizable o e 9 3 Resources 9 4 Creating the GU e 9 5 Creating the Plugin e 9 6 Issues and Problems ee 9 7 Adding Feedback 0000 ee ee 9 8 Summary 0 Creating Applications 10 1 Designing the GUI 2 20 02 0200 2000000 ee 10 2 Creating the MainWindow o 10 3 Finishing Up lt s s ied se Re Ra RA a ee ES 10 4 Running the Application e e A Installing Q 37
8. 4 WORKING WITH PLUGINS 4 3 THE DECORATION PLUGINS 6 Click Copyright Label Plugin Description Enter your copyright label below This plugin supports basic html markup tags for formatting the label For example lt B gt Bold text lt B gt lt gt Italics lt I gt note amp copy gives a copyright symbol lt b gt Map Created for FOSS4G2007 lt b gt lt br gt amp copy lt i gt Useless Maps LLC lt i gt Placement Bottom Right v Enable Copyright Label gt OK Cancel In the example above the first line is in bold the second created using lt br gt contains a copyright symbol followed by our company name in italics 4 3 2 North Arrow The North Arrow plugin places a simple north arrow on the map canvas At present there is xxTry It only one style available You can adjust the angle of the arrow or let QGIS set the direction automatically If you choose to let QGIS determine the direction it makes its best guess as to how the arrow should be oriented For placement of the arrow you have four options corresponding to the four corners of the map canvas Quantum GIS FOSS4G2007 29 4 3 THE DECORATION PLUGINS CHAPTER 4 WORKING WITH PLUGINS North Arrow Plugin North Arrow Plugin Properties Angle m Placement Bottom Left y Enable North Arrow y Set direction automatically OK Cancel 4 3 3 Scale Bar The Scale Bar
9. Loading a WFS Layer ee ee 39 16 reating a PostGIS Connection o a 40 17 Loading the Cities Layer from PostGIS 41 18 reating a Subset from the Cities Layer 42 19 reating a GRASS Location Using QGIS 46 20 Importing the Cities Shapefile into GRASS 47 21 Importing a Raster DEM into GRASS 47 22 reating a Buffer o 50 23 reating Contours from the DEM 50 24 Using Map Algebra 0 e 51 Chapter 1 Introduction The goal of this workshop is to not only introduce you to Quantum GIS QGIS but to show you how it can integrate with other members of the open source GIS stack 1 1 Topics Here are the topics we will cover Install QGIS View common file based data Symbolize your data Work with attributes and actions Digitize features Export map images Create data from text files Use the standard plugins that come with QGIS Export MapServer map files 10 Consume data from WMS and WFS servers 11 View and edit data in PostGIS 12 View edit and analyze GRASS vector and raster maps Ko We will also take a look at using Python to extend QGIS including how you can write your own applications using Python and PyQt 1 2 Tools For the workshop we will be using a LiveCD If you brought your own laptop
10. QGIS remembers and will load it the next time you start it up When you load a plugin new tools and menu items are added to the user interface The Tip 5 USING PLUGINS Most plugins add both a tool to the Plugins toolbar and an entry under the main Plugins menu The menu items are organized by sub menus since some plugins or plugin categories have multiple tools To use a plugin you can either click on the tool in the toolbar or use the menu Plugin Manager is shown below with all plugins loaded QGIS Plugin Manger Lala Gael Plugin Directory home gsherman qgis_08 1 bin lib qgis i To load a plugin click the checkbox next to the plugin and click Ok Name Version Description Add Delimited Text Layer Version 0 2 Loads and displays delimited text files containing x y coordinates M CopyrightLabel Version 0 1 Draws copyright information GPS Tools Version 0 1 Tools for loading and importing GPS data GRASS Version 0 1 GRASS layer Georeferencer Version 0 1 Adding projection info to rasters Graticule Creator Version 0 1 Builds a graticule Launcher Version 0 2 Launches a program or script from within QGIS NorthArrow Version 0 1 Displays a north arrow overlayed onto the map PostgresSQL Geoprocessing Version 0 1 Geoprocessing functions for woking with PostgreSQL PostGIS layers SPIT Version 0 1 Shapefile to PostgreSQL PostGIS Import Tool ScaleBar Version 0 1 Draws a scale bar WFS plugin Version 0 0001 Adds WFS layers to the
11. for actions For example if you have a point layer containing locations of images or photos along with a file name you could create an action to launch a viewer to display the image You could also use actions to launch web based reports for an Quantum GIS FOSS4G2007 19 2 5 ATTRIBUTES AND ACTIONS CHAPTER 2 GETTING STARTED attribute field or combination of fields specifying them in the same way we did in our Google search example Exercise 7 Creating an Attribute Action Create an action to do the Wikipedia lookup using the world_borders layer and the CN TRY_NAME field The URL needed for the lookup is http en wikipedia org wiki Add the country name field to the end of the URL when creating the action Quantum GIS FOSS4G2007 20 Chapter 3 Digitizing and Editing Data QGIS supports digitizing and editing of spatial features in a wide range of formats including shapefiles PostGIS layers and GRASS layers 3 1 Digitizing Our goal is to do some heads up digitizing from the world_mosaic raster We ll assume we Make sure are creating a brand new layer rather than editing an existing one As of version 0 8 QGIS the world only supports creation of shapefiles for editing although you could create a new PostgreSQL ant layer using SQL and edit it QGIS Exercise 8 Creating a New Shapefile We ll create a shapefile with an ID and NAME 1 Choose New Vector Layer from the Layer menu 2 Click on
12. import of our GUI in line 14 and the import of our resources file on line Our application needs to know where to find the QGIS installation Because of this we set the QGISHOME environment variable to point to the install directory of QGIS 0 9 In line 20 we store this value from the environment for later use Next we need to create our MainWindow class which will contain all the logic of our appli cation class MainWindow QMainWindow Ui MainWindow def _ init__ self QMain Window _ init__ self Required by Qt4 to initialize the UI self setupUi self Quantum GIS FOSS4G2007 61 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 D DD DD DO a 0 m 0 0 0 Aa Ya a a a Bb OU NN HH O 0 0 3J Da Bb 0 NY hh O 65 66 67 68 69 70 71 72 73 74 75 76 77 10 2 CREATING THE MAINWINDOW CHAPTER 10 CREATING APPLICATIONS Set the title for the app self set WindowTitle FOSS4G2007 Demo App Create the map canvas self canvas QgsMapCanvas Set the background color to light blue something self canvas setCanvasColor QColor 200 200 255 self canvas enableAntiA liasing True self canvas useQImageToRender False self canvas show Lay our widgets out in the main window using a vertical box layout self layout QVBoxLayout self frame self layout add Widget self canvas Create the actions for our tools and connect each to th
13. needs a couple more things First it needs a geometry column We purposely didn t include one when we created the table so we could use the AddGeometryColumn function to create it This function adds a geometry column to the table and then puts an entry in the geometry_columns table for us In line 55 we specify the table name the name we want for the geometry column the SRID feature type and the dimension of the feature The last thing to do is create a spatial index on the table so we get optimum performance when doing spatial searches and displaying the data in QGIS In line we have cobbled together the SQL to create the index The actual statement looks like this create index sidx_park_land on park_land USING GIST the_geom GIST_GEOMETRY_OPS 9 6 Issues and Problems Our plugin is now complete Now lets look at some of the things that are wrong with it or where we could improve it e We could use an improved GUI one that lets the user enter all the needed information on one dialog e The user can t specify field types e There is limited error checking in the dialog If you don t enter any fields the plugin fails There is no error checking on any of the database operations e There is no feedback from the plugin once it completes With all the issues it still servers as a primordial plugin that illustrates the process and helps get you started with your own plugin development 9 7 Adding Feedback Let s fix one of t
14. scenes This in turn can help you make the transition to using the modules from the GRASS command line If you look through the modules in the GRASS toolbox you ll see that there are a large number of tools available for working with your GRASS data In this section we ll look at a Quantum GIS FOSS4G2007 49 8 6 ANALYSIS CHAPTER 8 GRASS AND QGIS few examples of what you can do with the GRASS geoprocessing tools 8 6 1 Creating a Buffer A common GIS operation is to create a buffer You might want to examine the impact of development or establish setbacks to protect a critical resource With the GRASS toolbox we can quickly create a buffer using v buffer Exercise 22 Creating a Buffer Let s create a buffer of the cities layer Open your mapset containing the layer Load the cities layer Open the GRASS toolbox Under Buffer click on the v buffer module Enter a buffer distance of 0 1 Give the output map a name cities_buffer Click Add the buffer layer to the map and examine it Specifying a buffer distance in decimal degrees may not be intuitive For many geopro cessing operations you ll want to work in a projected coordinate system for a number of reasons 8 6 2 Creating Contours Another module allows us to create a contour map from a raster containing elevation or other data We can use the raster we imported earlier into our GRASS mapset to create contours Exercise 23 Creating Contour
15. something like this http en wikipedia org wiki CNTRY_NAME If you create this action for a world boundaries layer that has a CNTRY_NAME field you can use it to open the Wikipedia page for a country Let s create an action that does a Google search on the cities layer First we need to determine the URL needed to perform a search on a keyword This is easily done by just going to Google and doing a simple search then grabbing the URL from the address bar in your browser From this little effort we see that the format is http google com search q qgis where qgis is the search term Armed with this information we can proceed 1 Make sure the cities layer is loaded 2 Open the properties dialog by double clicking on the layer in the legend or right click and choose Properties from the popup menu 3 Click on the Actions tab Enter a name for the action for example Google Search 5 For the action we need to provide the name of the external program to run In this case we can use Firefox If the program is not in your path you need to provide the Aa Quantum GIS FOSS4G2007 18 CHAPTER 2 GETTING STARTED 2 5 ATTRIBUTES AND ACTIONS full path 6 Following the name of the external application add the URL used for doing a Google search up to but not included the search term 7 The text in the Action field should now look like this firefox http google com search q 8 Click on the drop down box con
16. table You can continue digitizing by starting editing again using the tool 3 2 Editing Your Features You probably noticed that as we were digitizing we couldn t correct any mistakes we made along the way Fortunately we can fix things up once we have completed the feature QGIS indicates the vertices or points with a large X when a layer is in edit mode The tools on the digitizing toolbar allow us to add delete and move the vertices to adjust a feature If you find areas where you were a bit careless or maybe should have been more detailed don t worry you can easily fix them Quantum GIS FOSS4G2007 22 CHAPTER 3 DIGITIZING AND EDITING 3 2 EDITING YOUR FEATURES 3 2 1 Setting the Snap Tolerance Before we can edit vertices we need to set the snapping tolerance This is the distance QGIS uses to search for the polygon and vertex you are trying to edit when you click on the map If you aren t within the snap tolerance QGIS won t find and select the vertex for editing Tolerance is set in map units so you may find you need to experiment to get it set right If you specify too big of a tolerance QGIS may snap to the wrong vertex especially if you are dealing with a large number of vertices in close proximity Set it too small and it won t find anything and it will pop up an annoying warning to that effect To set the snap tolerance choose Project Properties from the Settings menu and click on the General
17. the GRASS geoprocessing modules In this chapter we ll introduce the plugin and some of the ways you can use it to work with GRASS data 8 1 The GRASS Plugin The GRASS plugin is loaded from the Plugin manager just like all QGIS plugins When you load it a new toolbar will appear on the user interfacel PORN we T Q Normally in GRASS you open a mapset first then you can load a map layer With the QGIS GRASS plugin loaded we can open any GRASS layer we like without opening a mapset but first we must get some data into GRASS 8 2 Creating a Location GRASS stores data in a location which represents a specific area with a specific coordinate system In order to use GRASS data we must import it into a locat ion GRASS location Location Select location ak raster Create new location world_geo The GRASS location is a collection of maps for a particular territory or project lt Back Next gt Cancel The GRASS plugin is unique in that it creates its own toolbar 2This is not strictly true you can view external data sets without importing them 45 8 3 IMPORTING DATA CHAPTER 8 GRASS AND QGIS Exercise 19 Creating a GRASS Location Using QGIS Let s create a location for our world wide data 1 Start QGIS 2 Make sure the GRASS plugin is loaded 3 Load the world_borders shapefile 4 In the GRASS toolbar click on the tool to bring up the mapset wizard 5 Each locatio
18. the source layer active by clicking on it in the legend Use the select tool to select the feature s on the source layer Click on the tool Make the destination layer active by clicking on it in the legend Click on the tool Stop editing and save the changes What happens if the source and target layers have different schemas field names and types are not the same QGIS populates what matches and ignores the rest If you don t care about the attributes being copied to the target layer it doesn t matter how you design the fields and data types If you want to make sure everything feature and its attributes gets copied make sure the schemas match Quantum GIS FOSS4G2007 24 Chapter 4 Working with Plugins QGIS comes with 12 plugins that enhance and extend the application The standard plugins available with QGIS are Add Delimited Text Layer Loads and displays data from a delimited text file The text file must contain X and Y coordinates for each feature Only point data is supported by the plugin Copyright Label Displays copyright information on the map canvas You can customize the text style and placement of the label GPS Tools Tools to load and import GPS data as well as download to your GPS unit GRASS A full suite of GRASS tools for loading vector and raster maps digitizing features and using modules to import export and process data Georeferencer Georeference rasters b
19. visit the GRASS website at http grass itc it for more documentation and tutorials Quantum GIS FOSS4G2007 52 Chapter 9 Python Plugins Writing plugins in Python is much simpler than using C To create a PyQGIS plugin you need QGIS 0 9 Python PyQt and the Qt developer tools When QGIS starts up it scans certain directories looking for both C and Python plugins For a file shared library DLL or python script to be recognized as a plugin it has to have a specific signature For Python scripts it s pretty simple QGIS looks in the following locations under the installation directory 1 Linux and other Unix share qgis python plugins 2 Mac OS X Contents MacOS share qgis python plugins 3 Windows Asharel QGISYpython plugins Each Python plugin is contained in its own directory When QGIS starts up it will scan each subdirectory in share qgis python plugins and initialize any plugins it finds Once that s done the plugin will show up in the plugin manager Let s create a plugin to fill a gap in the QGIS interface This plugin will allow us to create a new PostGIS layer for us to digitize It will be a simple plugin and pretty rough but it illustrates how to get started writing your own PyQGIS plugins 9 1 Setting up the Structure The first thing we need to do is set up the structure for our plugin In this example we ll be developing our plugin on Linux but the method is the same just a
20. window wnd MainWindow Move the app window to upper left wnd move 100 100 wnd show run retval app exec_ exit QgsApplication exitQgis sys exit retval if _name_ _main_ main sys argv 10 4 Running the Application Now we can run the application and see what happens Of course if you are like most developers you ve been testing it out as you went along Before we can run the application we need to set some environment variables On Linux or OS X export LD_LIBRARY_PATH HOME qgis_09 1ib export PYTHONPATH HOME qgis_09 share qgis python export QGISHOME HOME qgis_09 For Windows set PATH C qgis PATH set PYTHONPATH C qgis python set QGISHOME C qgis Quantum GIS FOSS4G2007 65 10 4 RUNNING THE APPLICATION CHAPTER 10 CREATING APPLICATIONS In the case of Linux or OS X we assume that QGIS is installed in your home directory in qgis_09 For Windows QGIS is installed in C qgis When the application starts up it looks like this FOSS4G2007 Demo App To add the world_borders layer click on the tool and navigate to the data directory Select the shapefile and click to add it to the map Our custom fill color is applied and the result is FOS54G2007 Demo App Quantum GIS FOSS4G2007 66 CHAPTER 10 CREATING APPLICATIONS 10 4 RUNNING THE APPLICATION Creating a PyQGIS application is really pretty simple In less than 150 lines of code we have an applicat
21. 37 38 38 38 40 40 40 41 41 43 43 44 45 45 45 46 47 47 48 48 49 50 50 51 52 53 53 53 54 54 55 58 58 59 60 60 61 65 65 68 Tips 1 LOADING MORE THAN ONE LAYER 9 2 MISSING TOOLBARS gt oi s p a ek 2G na wR Ree awe Be ee ee R 10 3 VIEWING A SINGLE BAND OF A MULTIBAND RASTER aa aa 12 4 EDITING ATTRIBUTES 2 0 aa a a a a a a 18 5 USING PLUGINS 0 0 26 6 MAPSERVER EXPORT REQUIRES A QGIS PROJECT FILE 33 7 FINDING WMS AND WFS SERVERS 000080000 8 39 8 POSTGIS IMPORT PROBLEMS e 44 9 LEARNING MORE ABOUT GRARSI 0000008000048 52 10 DOCUMENTATION FOR PYQG S 67 Exercises 1 Loading the World Borders Laver aaau aaae 9 2 Loading the World Mosaic Raster 10 3 Changing Raster Transparency o e 11 4 Rendering Cities by Capital vs Non Capitall 13 5 Labeling Cities aa aaa a 14 6 hanging the Search Radius nauhaa aaa a 16 7 reating an Attribute Action o 20 8 reating a New Shapefile 0 o 21 9 Digitizing a Lake ee 22 10 opying Features Between Layers aoaaa aaa a 24 11 reate a Delimited Text Layer aaau aaa 27 12 reating a Graticule o 32 13 reating a Map File o eee ee 34 14 Loading a WMS Layer o 37 15
22. 43 0 0 016 9 11 29 2006 23 00 57 1 51 0573 179 4543 13 9 4 2 The first row is the header and contains the names of the fields in the file The delimiter is but we could have just as easily used or some other character Exercise 11 Create a Delimited Text Layer To create a layer 1 Open the Plugin Manager Enable the Add Delimited Text plugin 2 3 Click 4 Find the tool in the Plugins toolbar and click on it to bring up the plugin dialog To specify the text file click on the 5 button browse to the data directory and choose earthquakes_delim txt Click If the delimiter isn t already set it now and click to parse the text file again Enter a name for the layer Earthquakes From the drop down boxes choose the field names for the X and Y values 10 Click to add it to the map canvas 11 Close the dialog al COND Once the layer is added to the map canvas it behaves just like any other layer You can zoom in and out identify features and open the attribute table If you want to use the layer in the future you should save it to a shapefile Our completed dialog used to add the layer looks like this Quantum GIS FOSS4G2007 27 Ax Try It 4 3 THE DECORATION PLUGINS CHAPTER 4 WORKING WITH PLUGINS Greate a Layer from a Delimited Text File Delimited Text Layer Description fie fat Y Toos Binn Hew gine vi lw Lee TETALI een la Eiin aa 408 Select a delimit
23. AND ACTIONS CHAPTER 2 GETTING STARTED Tip 4 EDITING ATTRIBUTES Not all layer types can be edited It depends on the capabilities of the underlying data provider To see if your layer type supports editing open the vector properties dialog and look in the General section of the Metadata tab Searching To search the attribute table 1 Enter the search string in the Search for box 2 Choose the field you want to search from the drop down list 3 Change the select drop down to the option you want You can select the matches select them and bring to the top of the table or show only matching records 4 Click Query Builder To create more complex queries use the Query Builder by clicking on the button If you have used other GIS software the layout of the Query Builder will look familiar You can either build the query by pointing and clicking and a little typing or by entering the SQL where clause directly As an example try selecting all the cities that have a population less than 100 000 but are capital cities Once you make the selection return to the attribute table and promote the results to the top 2 5 3 Attribute Actions Attribute actions are a handy way to run an external program and pass it one or more fields associated with a feature For example you could create actions to display an image do a web search or create a report from a database based on the value An action looks
24. FILES Map Width Width of the output image in pixels Map Height Height of the output image in pixels Map Units Units of measure used for output Image type Format for the output image generated by MapServer Web Template Full path to the MapServer template file to be used with the map file Web Header Full path to the MapServer header file to be used with the map file Web Footer Full path to the MapServer footer file to be used with the map file Only the Map file and QGIS project file inputs are required to create a map file however you may end up with a non functional map file depending on your intended use Although QGIS is good at creating a map file from your project file it may require some tweaking to get the results you want but it s still way better than writing a map file from scratch Exercise 13 Creating a Map File Let s create a map file using our world borders and cities layers Load the world_borders and cities layers into QGIS Change the colors and symbolize the data as you like Save the project using Save Project from the File menu Open the exporter by clicking on Export to MapServer Map in the File menu Enter a name for your new map file Browse and find the project file you just saved Enter a name for the map Enter 600 for the width and 400 for the height Our layers are in decimal degrees so we don t need to change the units Choose png for the image type Click to ge
25. OM drive Gentoo and 2 If the computer is running reboot it using the Start menu uses the 3 If the computer is off turn it on Gnome 4 When the boot prompt appears press Enter ida 5 When prompted for the keymap press Enter 6 Wait while the system comes up 7 At the login screen enter qgisuser as the user name 8 Enter qgisuser as the password If everything goes well you should be looking at a Linux Gnome desktop 2 2 Starting QGIS To start QGIS choose Qgis from the Applications Gis menu You should now be looking at the QGIS map canvas and an empty legend 2 3 Viewing Data Let s get started viewing some data by loading some vector and raster datasets 2 3 1 Viewing Vector Data Exercise 1 Loading the World Borders Layer We ll start with vector data and load the world borders layer 1 Click on the tool in the toolbar or choose Add a Vector Layer from the Layer menu Navigate to the data directory home qgisuser data qgis Make sure the Files of type drop down box has the ESRI Shapefiles filter selected Choose world_borders shp Click o e w N Tip 1 LOADING MORE THAN ONE LAYER You can load more than one layer at a time by using the Shift or Ctrl keys in the open dialog to select multiple layers 2 4 SYMBOLIZING YOUR DATA CHAPTER 2 GETTING STARTED You should now have the world_borders shapefile loaded and displayed in an ugly color We ll fix that in jus
26. PostGIS layer you can specify a query to limit the features that are returned For example say we only want to display cities with populations of 4 million or more We can do this when we add the cities layer effectively creating a new or subset layer Quantum GIS FOSS4G2007 Al 7 1 VIEWING DATA CHAPTER 7 VIEWING AND EDITING DATA IN POSTGIS Exercise 18 Creating a Subset from the Cities Layer 1 Click on in the toolbar 2 Choose your connection from the drop down box 3 Click 4 Double click on the cities layer to bring up the query builder 5 Double click the population field to add it to the where clause 6 Click the button 7 In the where clause box type 4000000 8 Click to test the query and see how many features match 9 Click ok The query now shows up in the Sql column of the cities layer in the layer list 10 Click to add our subset layer to the map PostgreSQL Query Builder Table cities in database gis_data on host localhost user gsherman Fields Values gid name country population capital the_geom Operators SQL where clause population gt 4000000 Modifying the Subset xxTry It Once you have a subset layer loaded you can tweak the query to modify it without dropping it from the map and adding it again In fact you can do this with any PostGIS layer 1 Open the vector properties dialog by double clicking on the PostGIS layer in the
27. QGIS canvas a Select All Clear All Ol Close Let s take a look at some of the key plugins available in QGIS 4 2 The Delimited Text Plugin The delimited text plugin allows you to treat a text file as a layer in QGIS The text file must have the following characteristics 1 Plain text format 2 Delimited with any character Quantum GIS FOSS4G2007 26 CHAPTER 4 WORKING WITH PLUGINS 4 2 THE DELIMITED TEXT PLUGIN 3 A header row with the field names 4 An X and Y field can be in any coordinate system The plugin parses your text file and adds it to the map canvas as a layer If you like you can save it to a shapefile by right clicking on the layer name in the legend and choosing Save as shapefile from the popup menu Let s look at an example We have been lucky enough to download some historical earthquake data and manipulate it using a bit of Ruby that s another story to create a delimited text file in the following format event_date event_time latitude longitude depth magnitude 06 29 1898 18 36 00 0 52 0000 172 000010 017 6 10 11 1898 16 37 32 7 50 7100 179 5 0 016 9 07 14 1899 13 32 00 0160 0000 150 0 0 017 2 09 04 1899 00 22 00 0 160 0000 142 0125 017 9 09 04 1899 04 40 00 0160 0000 142 0 0 016 9 09 10 1899 17 04 00 0160 0000 140 0 25 017 4 09 10 1899 21 41 00 0160 0000 140 0 25 0 8 0 09 17 1899 12 50 00 0159 0000 136 0 0 016 9 09 23 1899 11 04 00 0160 0000 1
28. Shuffling Quantum GIS into the Open Source GIS Stack Free and Open Source Software for Geospatial FOSS4G Conference Victoria BC Gary E Sherman September 24 2007 Contents 1 Introduction A 1 2 Tools aoe ees eee 1 4 Conventions etting Started 4 5 2 1 Using the LiveCD 2 2 Starting QGIS 2 3 Viewing Data 2 3 1 Viewing Vector Datal o o eG 2 3 2 Viewing Raster Datal e e s ece wos e oe eine Wa KR RR 2 4 Symbolizing Your Data o mie os eces wie e aia aa e E TR K ee 2 4 1 Raster Rendering ooo a 2 4 2 Vector Rendering ooo a 2 5 Attributes and AGonSl 2 5 1 Identifying Features ooa aa a 2 5 2 Using the Attribute abla a 2 5 3 Attribute Actions 2 ooa ee Digitizing and Editing 3 1 Digitizing san k A a A A a a A A A ae Boe Gee CA a bee a ee a ae ew ee Be dee Severn at Geta ee oe Gro as he A Working with Plugins 4 1 The Plugin Manager a o E e ao E NN 4 3 1 Copyright Label o e e oe ce he E A E a a e Cop ee Gee Oe ey A 4 3 3 Scale Bar sa os 2 paad ra RAOR a Ae a e A na A ek a e e a Geet E e 4 5 Graticule Creator 22 2 2622 ipa deetan d a a Da dr amp e o do Ge ca Making MapServer Map Files O E E See ae sees ge gs ees Pee eee Pee ee ee ee ee Be EE 5 3 Testing the Map File NNNNN O oo o o 10 11 13 15 15 16 18 21 21 22 23 23 23 25
29. This completes the implementation of all our tools except one the add layer tool Let s look at it next Add an OGR layer to the map def addLayer self file QFileDialog getOpenFileName self Open Shapefile Shapefiles shp fileInfo QFileInfo file Add the layer layer QgsVectorLayer file fileInfo fileName ogr if not layer isValid return Change the color of the layer to gray symbols layer renderer symbols symbol symbols 0 symbol set FillColor QColor fromRgb 192 192 192 Add layer to the registry QegsMapLayerRegistry instance addMapLayer layer Set extent to the extent of our layer self canvas setExtent layer extent Set up the map canvas layer set cl QgsMapCanvasLayer layer layers cl self canvas setLayerSet layers In the addLayer method we use a QFileDialog to get the name of the shapefile to load This is done in line 96 Notice that we specify a filter so the dialog will only show files of type Shp Next in line 97 we create a QFilelnfo object from the shapefile path Now the layer is ready to be created in line 100 Using the QFilelnfo object to get the file name from the path we specify it for the name of the layer when it is created To make sure that the layer is valid and won t cause any problems when loading we check it in line If it s bad we bail out and don t add it to the map canvas Normally l
30. This renderer renders the features based on the value of a field starting with a color for the minimum value and ending with a color for the maximum value The field used to classify the data must be numeric Unique Value This renderer displays all features of the same type in the same color You can use any field in the attribute table as the classification field For each unique value you must set the color and fill style or accept the random defaults assigned by QGIS The choice of renderer depends on what you are trying to visualize Here are some exam ples 1 You want to display world population to portray the most populated countries Grad uated Symbol 2 You want to create a map showing rock types or soil vegetation or any other thing Unique Value 3 You want to render earthquakes by magnitude and aren t too concerned with the class breaks Continuous Color To use a renderer select if from the Legend Type drop down list When you select a renderer the dialog will change to provide the needed controls for setting things up These are different for each renderer Exercise 4 Rendering Cities by Capital vs Non Capital Take a shot at rendering the cities layer to display capital cities in a different color or style than non capital cities While you re at it fix the ugly random color for your world_borders layer Let s take a look at the vector properties dialog along with some of the options and tabs
31. ase of 0 8 With the release of 0 9 development of standalone applications using either C or Python is possible In this chapter we ll take a brief look at the process for creating a standalone Python appli cation The QGIS blog has several examples of creating PyQGIS applications We ll use one of them as a starting point to get a look at how to create an application The features we want in the application are e Load a vector layer e Pan e Zoom in and out e Zoom to the full extent of the layer e Set custom colors when the layer is loaded This is a pretty minimal feature set Let s start by designing the GUI using Qt Designer 10 1 Designing the GUI Since we are creating a minimalistic application we ll take the same approach with the GUI Using Qt Designer we create a simple MainWindow with no menu or toolbars This gives us a blank slate to work with To create the MainWindow 1 Create a directory for developing the application and change to it 2 Run Qt Designer es The New Form dialog should appear If it doesn t choose New Form from the File menu Choose Main Window from the templates forms list Click Resize the new window to something manageable NI Oa a Find the Frame widget in the list under Containers and drag it to the main window you just created Click outside the frame to select the main window area 9 Click on the tool When you do the frame will expand
32. ayers are added with a random color Here we want to tweak the colors for the layer to make a more pleasing display Plus we know we are going to add the world_borders layer to the map and this will make it look nice on our blue background To change the color we need to get the symbol used for rendering and use it to set a new fill color This is done in lines through All that s left is to actually add the layer to the registry and a few other housekeeping items lines through 119 This stuff is standard for adding a layer and the end result is the world borders on a light blue background The only thing you may not want to do is set the extent to the layer if you are going to be adding more than one layer in your application Quantum GIS FOSS4G2007 64 125 130 135 CHAPTER 10 CREATING APPLICATIONS 10 3 FINISHING UP That s the heart of the application and completes the MainWindow class 10 3 Finishing Up The remainder of the code shown below creates the QgsApplication object sets the path to the QGIS install sets up the main method and then starts the application The only other thing to note is that we move the application window to the upper left of the display We could get fancy and use the Qt API to center it on the screen def main argv create Qt application app QApplication argv Initialize qgis libraries QegsApplication setPrefixPath qgis_prefix True QegsA pplication initQgis create main
33. d download data as well as open existing GPX files QGIS uses gpsbabel to import other formats and for GPS downloading and uploading oper ations Fortunately gpsbabel runs on the same platforms as QGIS so if you can run QGIS you can use it with your GPS It supports 100 formats and a good selection of GPS hard ware For upload download if you have a Garmin or Magellan unit you should be good to go For others see the format list on the web page to see if yours is listed there When you load the plugin the first thing to notice is the four tabs across the top of the GPS plugin dialog The first two Load GPX file and Import other file allow you to load data stored on a disk CD or maybe a thumb drive The last two tabs Download from GPS and Upload to GPS provide the tools needed to move data to and from your unit Using the functions available on the Import other file tab you can convert and import any format supported by gpsbabel More information on using the GPS plugin can be found in the QGIS User Guide http www gpsbabel org Quantum GIS FOSS4G2007 31 4 5 GRATICULE CREATOR CHAPTER 4 WORKING WITH PLUGINS 7 GPS Tools Load GPX file Import other file Download from GPS Upload to GPS GPX is the GPS eXchange file format which is used to store information about waypoints routes and tracks Select a GPX file and then select the feature types that you want
34. dapt some of the file system commands as appropriate for your platform QGIS is installed in a directory named qgis_09 in our home directory Let s create the directory for the plugin mkdir qgis_09 share qgis python plugins new_layer To get started we need to create the following files in the new_layer directory we ll need some additional files in a bit init__ py resources py resources qre newlayer py Ae 00 IN re 9 2 Making the Plugin Recognizable Initializing the plugin is done in the __init__ py script For our NewLayer plugin the script contains 1 load NewLayer class from file newlayer py 2 from newlayer import NewLayer 3 def name 4 return New PostGIS layer 53 j o 0 N Q Ww 9 3 RESOURCES CHAPTER 9 PYTHON PLUGINS def description return Creates a new empty Postgis layer def version return Version 0 1 def classFactory iface return NewLayer iface The mandatory things a plugin must return are a name description and version all of which are implemented in our script above Each method simply returns a string with the appropriate information The other requirement is the classFactory method that must return a reference to the plugin itself line 10 after receiving the iface object as an argument With this simple code QGIS will recognize our script as a plugin 9 3 Resources In order to have a nice icon for our plugin we need a resources file
35. e in self toolZoomOut QgsMapToolZoom self canvas True true out Quantum GIS FOSS4G2007 62 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 CHAPTER 10 CREATING APPLICATIONS 10 2 CREATING THE MAINWINDOW Lines through are the basic declaration and initialization of the MainWindow and the set up of the user interface using the setupUi method This is required for all applica tions Next we set the title for the application so it says something more interesting than Main Window line 30 Once that is complete we are ready to complete the user interface When we created it in Designer we left it very sparse just a main window and a frame You could have added a menu and the toolbar using Designer however we ll do it with Python In lines 33 through 38 we set up the map canvas set the background color to a light blue and enable antialiasing We also tell it not to use a QImage for rendering trust me on this one and then set the canvas to visible by calling the show method Next we set the layer to use a vertical box layout within the frame and add the map canvas to it in line Lines 48 to 63 set up the actions and connections for the tools in our toolbar For each tool we create a QAction using the icon we defined in our resources file Then we connect up the activated signal from the tool to the method in our class that will handle the action This is similar to how we set things up i
36. e appropriate method self actionAddLayer QAction QIcon foss4g2007 mActionAddLayer png Add Layer self frame self connect self actionAddLayer SIGN ALU activated self addLayer self actionZoomIn QAction QIcon foss4g2007 mActionZoomIn png Zoom In self frame self connect self actionZoomIn SIGNAL activated self zoomIn self actionZoomOut QAction QlIcon foss4g2007 mActionZoomOut png A Zoom Out self frame self connect self actionZoomOut SIGNAL activated self zoomOut self actionPan QAction Qlcon foss4g2007 mActionPan png Pan self frame self connect self actionPan SIGNAL activated self pan self self actionZoomFull QAction Qlcon foss4g2007 mActionZoomFulExtent png Zoom Full Extent self frame connect self actionZoomFull SIGNAL activated self zoomFull Create a toolbar self toolbar self addToolBar Map Add the actions to the toolbar self toolbar addAction self actionAddLayer self toolbar addAction self actionZoomIn self toolbar addAction If toolbar addAction self actionPan se self actionZoomOut self toolbar addAction self actionZoomFull Create the map tools self toolPan QgsMapToolPan self canvas self toolZoomIn QgsMapToolZoom self canvas False 4 fals
37. e there are one or more lakes You ll find some nice candidates in central North America Africa and eastern Russia To get a gross approximation of the lake we can just zoom in until we only see the lake If we want a detailed representation of the lake we need to zoom in much closer and pan around the map as we digitize 2 If you aren t already in edit mode click the tool 3 Click on the tool in the digitizing toolbar 4 To digitize click with the left mouse button and begin moving along the shoreline clicking at each location where there is a change in direction 5 If you get to the edge of the map canvas and need to pan to see more of the lake don t use the pan tool but instead hold down the Space bar and move the mouse to pan 6 If you find out that you need to change the zoom level to effectively digitize you can zoom in and out using the mouse wheel 7 To complete the lake right click at the final point This brings up the attribute dialog where we enter the attribute values for the feature Enter an ID number and a NAME for the lake To actually save the changes we need to stop editing by clicking on the tool in the toolbar Or you can right click on the layer name in the legend and choose Allow editing to toggle editing off A confirmation dialog appears and you have to choose to save the edits The lake now appears like a regular polygon feature and we can both identify it and view the attribute
38. e we are creating the table with an integer id field that will be the primary key We then iterate through the field list appending the appropriate code to the SQL statement line 41 Once we have all the fields added to the SQL statement we chop off the trailing characters we don t want line 43 and then add the closing parenthesis to complete the statement line 44 Now we are ready to connect to the database and create the table To access the database we are using psycopg http www initd org In order to connect we need to specify the data source name DSN with the name of the database the user and a password if necessary If we are running both QGIS and PostgreSQL on the same machine we usually don t need to specify a password In this case the DSN will look something like this dbname gis_data user gsherman To get the DSN we prompt the user with a QInputDialog in line 47 Quantum GIS FOSS4G2007 57 9 6 ISSUES AND PROBLEMS CHAPTER 9 PYTHON PLUGINS Database DSN Enter the DSN for connecting to the database dbname db user user dbname gis_data user gsherman X Cancel dd ox If the user enters a DSN then we can proceed with the connection to the database in line We get a cursor from the connection in line 51 and then execute the SQL statement to create the table and commit the change in lines 52 through 53 This creates the table but for it to be a valid layer and ready for us to use it
39. ed text file containing x and y vg A 419 y coordinates that you would like to use as a point HE layer and this plugin will do the job for you helio mre u US Use the layer name box to specify the legend name for the new laver Use the delimiter box to specifv f l Delimited text file gis_data earthquakes_delim txt ma Layer name earthquakes delim Delimiter l X field longitude xl Y field latitude x Sample text d d N U1JU1 19UZjU5 2U 19 8 52 38UU 10 45 U U a 01 17 1903 16 05 07 1 50 8500 175 16 0 0 02 05 1903 18 26 00 0 52 0000 175 0000 0 06 02 1903 13 17 21 4 61 5600 158 54 0 0 Y N 08 27 1904 21 56 20 5 f4 6600 148 08 0 0 a 02 14 1905 08 46 38 4 40 7300 178 55 0 0 L G Dy c TBN Hep Parse Add ayer close 4 3 The Decoration Plugins The Decoration plugins include the following 1 2 3 Copyright Label North Arrow Scale Bar These decorate the map by adding cartographic elements 4 3 1 Copyright Label The title of this plugin is a bit misleading you can add any random text to the map 1 2 3 Make sure the plugin is loaded Click on the tool on the Plugins toolbar Enter the text you want to place on the map You can use HTML as shown in the example Choose the placement of the label from the drop down box Make sure the Enable Copyright Label checkbox is checked Quantum GIS FOSS4G2007 28 CHAPTER
40. eed to specify the parent In a plugin the parent is the main window of QGIS The iface object that we stored during initialization allows us to get the reference to the main window in line Once the action is created we can add it to both the toolbar and the Plugins menu lines 23 and Pa That takes care of initializing the GUI for the plugin The other thing we need to do is clean up after ourself when the plugin is unloaded The unload method takes care of this by removing the menu item and the tool from the toolbar lines 28 and 29 This takes care of the initialization stuff and getting our plugin to load and unload nicely Now let s look at the code that does the actual work It s all contained in the run method def run self Get the user input starting with the table name table name QInputDialog getText None Table Name Name for new PostGIS layer if table namel 0 length gt 0 Get the field names and types fields QInputDialog getText None Field Names Fields separate with a comma parts fields 0 split Create the SQL statement sql create table table_ name 0 id int4 primary key for fid in parts sql fld varchar 10 sql sql 0 2 sql Connect to the database First get the DSN dsn QInputDialog getText None Database DSN Enter the DSN for connecting to the database dbname db user user
41. en the properties dialog Click on the Labels tab Check the Display labels checkbox to enable labeling Choose the field to label with We ll use NAME Enter a default for cities that have no name The default label will be used each time QGIS encounters a city with no value in the NAME field 8 Click Now we have labels How do they look They are probably too big and poorly placed in relation to the marker symbol for the city Click on the Font Style tab and use the Font and Colour buttons to set the font and color To change the position of the font relative to the feature Quantum GIS FOSS4G2007 14 CHAPTER 2 GETTING STARTED 2 5 ATTRIBUTES AND ACTIONS 1 Click on the Font Alignment tab 2 Change the placement by selecting one of the radio buttons in the Placement group To fix our labels choose the Right radio button 3 Click to see your changes without closing the dialog Things are looking better but the label is still too close to the marker To fix this we can use the options on the Position tab Here we can add offsets for the X and Y directions Adding an X offset of 5 will move our labels off the marker and make them more readable Of course if your marker symbol or font is larger more of an offset will be required The last adjustment we ll make is to buffer the labels This just means putting a backdrop around them to make them stand ou
42. he cities are displayed over the raster oe Ww bv Don t worry about the ugliness we ll fix that next 2 4 Symbolizing Your Data QGIS gives you a good selection of rendering options for your raster and vector data These options are accessed using the properties dialog for a layer We ll start with the raster Quantum GIS FOSS4G2007 10 CHAPTER 2 GETTING STARTED 2 4 SYMBOLIZING YOUR DATA first 2 4 1 Raster Rendering Exercise 3 Changing Raster Transparency The raster we loaded has an alpha transparency channel When loaded into QGIS the oceans are set to transparent giving things a ragged look To get the oceans back 1 Double click on the world_mosaic layer in the legend to open the raster properties dialog 2 In the Transparent drop down box change the value from Alpha to Not Set 3 Click Raster Layer Properties Symbology General Metadata Pyramids Histogram Display Color Image Grayscale Image Multiband Image Notes Invert Color Map This is a multiband image You can choose to Am render it as grayscale or ai color RGB For color None Full images you can ns S Transparency Color Image r Grayscale Image Color Gray Not Set Red E Std Deviations 0 Green 5 Color Map Grayscale Transparent The oceans have returned Let s reopen the raster properties dialog and take a quick look at the options on each
43. he small problems by adding some feedback at the end of the process We ll just add a message box to tell the user that everything is done and to check the database to make sure the table was created Quantum GIS FOSS4G2007 58 CHAPTER 9 PYTHON PLUGINS 9 8 SUMMARY To do this we just add the following code after line 62 show the user what happened 63 QMessageBox information None Results Table str table_name 0 64 has been created Check your database to confirm When the table is created the user sees this Results Table park_land has been created Check your database to confirm dor 9 8 Summary Writing a QGIS plugin in Python is pretty easy Some plugins won t require a GUI at all For example you might write a plugin that returns the map coordinates for the point you click on the map Such a plugin wouldn t require any user input and could use a standard Qt QMessageBox to display the result You can also write plugins for QGIS in C but that s another story You can find tutorials on writing QGIS plugins in both C and Python on the QGIS blog at http blog qgis org Quantum GIS FOSS4G2007 59 Chapter 10 Creating Applications One of the goals of QGIS is to provide not only an application but a set of libraries that can be used to create new applications This goal has been realized with the refactoring of libraries that took place after the rele
44. ibutes You may have noticed when we were editing attributes back in 2 5 2Jon page 17 that a couple of the buttons on the attribute table dialog were disabled These are the buttons to add or delete a column While these don t work for a shapefile they do for a PostGIS layer For example to add a column to the attribute table for the cities layer 1 Make sure the cities layer is loaded Make the layer active by selecting it in the legend just click on its name Open the attribute table by clicking on the tool Click Click the button the one with the yellow starburst 6 Let s add a Visited column so we can flag which cities we ve been to e WwW N al 7 Enter visited as the column name Quantum GIS FOSS4G2007 43 7 3 LOADING DATA CHAPTER 7 VIEWING AND EDITING DATA IN POSTGIS 8 Choose varchar 30 as the type 9 Click We now have a new column in the table We can enter values into the column using the editing capabilities of the attribute table or we could do a bulk update using a SQL query from psql the PostgreSQL interactive terminal This provides a convenient way to create a new column To commit the changes click the button and save the changes Likewise you can delete a column Start editing the attribute table then click the button and select the column to delete from the popup dialog 7 3 Loading Data Thus far we assumed you already had data in PostGIS QGIS provides a way to
45. if dsn 0 length gt 0 con psycopg connect str dsn 0 curs con cursor curs execute str sql con commit add the geometry column curs execute select AddGeometryColumn str table_name 0 A the geom 4326 POLYGON 2 con commit create the GIST index curs execute create index sidx_ str table_name 0 on str table name 0 USING GIST the geom GIST_GEOMETRY_OPS con commit The first thing we need to do is use the QInputDialog to get the name of the table to create This is done in line 32 where we prompt for it Quantum GIS FOSS4G2007 56 CHAPTER 9 PYTHON PLUGINS 9 5 CREATING THE PLUGIN Name for new PostGIS layer park_land X cancel dd ox In line 34 we check to see if the user actually entered anything before proceeding Next we need to get the field names For this example we are keeping it very simple Every field will be a varchar 10 meaning we can store up to 10 characters in it If we really want to make this plugin useful we would need to provide a way for the user to specify the type In line 36 we prompt the user to enter a comma delimited list of field names u fieldName MACES Fields separate with a comma name unit X Cancel 4i ok We then split this list into its components for use in constructing the SQL statement line 38 Line 40 contains the first part of the SQL statement Not
46. ing Data To import data you could use among others the v in ogr or r in gdal modules from the GRASS command line We ll use the QGIS GRASS plugin to do the work for us One thing to remember when using the plugin to import data into GRASS you must load the layer you want to import into QGIS then use the import module Quantum GIS FOSS4G2007 46 CHAPTER 8 GRASS AND QGIS 8 3 IMPORTING DATA 8 3 1 Importing Vectors Let s start out by importing our cities shapefile into GRASS Exercise 20 Importing the Cities Shapefile into GRASS 1 2 DONDA w Add the cities shapefile to QGIS If it s not already open open the mapset we just created using the tool on the GRASS toolbar Open the GRASS toolbox by clicking on the tool Under Import locate v in ogr and click on it to bring up the OGR import module From the drop down list select the cities layer Name the layer cities Click to start the import Review the results on the Output tab Click to add the new GRASS layer to the map canvas Close the GRASS toolbox and examine the new layer You might have noticed on the Output tab that it not only shows the processing but the actual GRASS command used to perform the operation This is a good way to learn and understand how the GRASS modules are used The new cities layer behaves like any other vector layer in QGIS You can open the It will take attribute table and identify fea
47. ion that can load a shapefile and navigate the map If you play around with the map you ll notice that some of the built in features of the canvas also work including mouse wheel scrolling and panning by holding down the Space bar and moving the mouse Some sophisticated applications have been created with PyQGIS and more are in the works This is pretty impressive considering that this development has taken place even before the official release of QGIS 0 9 Tip 10 DOCUMENTATION FoR PYQGIS Whether you are writing a plugin or a PyQGIS application you are going to need to refer to both the QGIS API documentation http qgis org and the PyQt Python Bindings Reference Guide http www riverbankcomputing com Docs PyQt4 pyqt4ref html These documents provide information about the classes and methods you ll use to bring your Python creation to life Quantum GIS FOSS4G2007 67 Appendix A Installing QGIS To install QGIS point your web browser at http qgis org and find the downloads section There you will find packages for the major platforms including Linux Mac OS X and Windows You have several options for installing depending on your platform 1 Install using the Mac OS X framework packages from kyngchaos com 2 Use the Windows installer 3 Install the deb or rpm for your Linux version 4 Build from source QGIS depends on a number of other open source packages When ins
48. legend Quantum GIS FOSS4G2007 42 CHAPTER 7 VIEWING AND EDITING DATA IN POSTGIS 7 2 EDITING DATA or right clicking and choosing Properties from the popup menu 2 Click on the General tab 3 Click on at the bottom right of the dialog 4 Edit the query using the same methods we used to create the original subset layer 5 6 Click to apply the query Close the properties dialog 7 1 4 Creating a View With a bit of SQL you can create a view Think of it as a permanent subset or superset of your layer To make our layer of cities with greater than 4 million people more permanent we create a view using psql or PgAdminIII create view big_cities as select from cities where population gt 4000000 The big_cities layer now shows up in our list when we go to add a PostGIS layer When we add it to the map it contains only those cities matching our criteria QGIS found the view automatically If you were to look in the geometry_columns table you would see there is no entry for it If you checked the box to Only look in the geome try_columns table when you created your PostGIS connection you won t see your view in the layer list 7 2 Editing Data Editing PostGIS data is done exactly like we described in Section 3 1 on page All the techniques described previously work with PostGIS layers There are a couple of things we can do with PostGIS layers that can t be done with other types when it comes to editing attr
49. load shapefiles into PostGIS using the SPIT plugin To load shapefiles add them to the list using the button You can change the SRID name of the geometry column the schema to load it into and the name of the database table to create if you aren t happy with the default SPIT Shapefile to PostGIS Import Tool Shapefile to PostGIS Import Tool PostgreSQL Connections madison Shapefile List Add Remove Remove All Use Default SRID v Use Default Geometry Column Name SRID 4326 Geometry Column Name the geor Global Schema public File Name Feature Class Features DB Relation Name home gsherman desktop_gis_data grid2x2 shp LINESTRING 272 grid2x2 home gsherman desktop_gis_data cities shp POINT 606 cities D Import iJ Close When you click each of the shapefiles in the list will be imported into PostGIS Tip 8 PosTGIS IMPORT PROBLEMS You may encounter problems using SPIT to import your data into PostGIS SPIT isn t particularly adept at handling errors or irregularities in your data Fortunately PostGIS comes with the shp2pgsql command line utility to load shapefiles If you encounter trouble with SPIT try using shp2pgsql1 to do the job Quantum GIS FOSS4G2007 44 Chapter 8 GRASS and QGIS The GRASS plugin provides access to GRASS from within QGIS This includes the ability to view edit and create data as well as perform analysis using
50. lt Z lt 2 lt Z2 2 2 lt Z Z2 2 lt 2 Search for in NAME Search select ei Advanced Close Besides just viewing the attributes for your layer you can use the attribute table dialog to e Select features by highlighting them They will be highlighted on the map as well e Once you have selected some rows you can move them to the top of the table invert the selection or copy it to the clipboard using the tools in the toolbar at the top of the dialog Sort rows by any of the field column names Edit attributes Search the table by any field Use the advanced query builder to perform more complex searches The dialog also allows you to create or delete a new column but this functionality only works with PostGIS layers Editing Attributes To edit one or more field values Press Enter 7 Tab Click on the button Locate the row and field you want to edit Double click on the field contents to enable editing Edit the contents or click on another row to make the change stick When done click on A dialog confirming your changes will popup If you want to save your edits click Yes otherwise click to discard your edits You might have noticed that Alice Springs has a population of 99 Surely there must be x Try It more people living there Try changing it to something more respectable Quantum GIS FOSS4G2007 17 xx Try It 2 5 ATTRIBUTES
51. lude editing view support and subset layers 7 1 Viewing Data Support for PostGIS is part of core QGIS you don t have to load a plugin to access it Before you can access PostGIS data you obviously need a PostgreSQL database with PostGIS We won t go into the details of the installation process but rather assume we have a properly configured database ready for our use 7 1 1 Creating a Connection In order to get at the data in our database we need to create a connection This requires some information about the database server the database and your login information Exercise 16 Creating a PostGIS Connection To create a new connection 1 Click on in the toolbar Click Enter a name for the connection this can be anything handy to remember Enter the host name If your PostGIS database is on the same machine this will be localhost Enter the name of the database that houses your data livecd Enter the port The default PostgreSQL port is 5432 Enter the user name qgisuser Enter the password you may not need one if running QGIS on the same machine as PostgreSQL 9 Click to see if you got things correct 10 Click to save the connection Ae WwW bd CON DH Ot If access to your database requires a password you can have QGIS store it for you however this may be a security risk depending on your environment QGIS searches all the tables in your database looking for those that have a spatial column
52. mber of bands data type projection pixel size and band properties Pyramids Tab Using pyramids helps speed up the display of a raster at smaller scales zoomed out The Pyramids tab allows you to build pyramids for a raster Make sure to read the warnings as this process will alter your original image The available pyramids for your raster are displayed in the right hand panel If a pyramid is available for a given resolution the little pyramid icon will be present without a red X over it Histogram Tab The histogram tab allows you to view the distribution of the bands or colors in your raster You must first generate the raster statistics by clicking the button You can choose Quantum GIS FOSS4G2007 12 CHAPTER 2 GETTING STARTED 2 4 SYMBOLIZING YOUR DATA which bands to display by selecting them in the list box at the bottom right of the dia log Once you view the histogram you ll notice that the band statistics have been populated on the Metadata tab 2 4 2 Vector Rendering QGIS provides four renderers to symbolize your data Single Symbol This uses a single symbol for point layers a simple outline for line layers and a fill color for polygons All features in the layer are rendered the same way Graduated Symbol This renderer allows you to symbolize features based on a number of classes Each class is composed of a range of values The field used to render the features must be numeric Continuous Color
53. n is stored in a directory Select an existing data directory or create a new one for storing the location 6 Click 7 We can use this wizard to create a new mapset within an existing location or create a new location altogether Click Create new location radio button 8 Enter a name for the location we ll use world_geo 9 Click 10 Define the projection by clicking on the Projection radio button to enable the pro jection list 11 We are using WGS 84 geographic Since we happen to know that its SRID is 4326 we enter it in the search box 12 Click to select the projection 13 Click 14 To define the default region enter the bounds in the north south east and west direction Fortunately these are already correct for our world geographic location 180 90 180 90 15 Click 16 We need to define a mapset within our new location Name it whatever you like your username is a good choice 17 Check out the summary to make sure it s correct 18 Click 19 The mapset and location are created and opened as the current working set 20 Notice that some of the tools in the GRASS toolbar that were disabled are now enabled for us to use If that seemed like a lot of steps it s really not all that bad and a very quick way to create a location Our location is now ready for use To view the default region click the Display Current Grass Region tool Now we are ready to import some data into GRASS 8 3 Import
54. n the plugin example Once we have the actions and connections we need to add them to the toolbar In lines through 72 we create the toolbar and add each tool to it Lastly we create the three map tools for the application lines through 77 We ll use the map tools in a moment when we define the methods to make our application functional Let s look at the methods for the map tools A Set the map tool to zoom in def zoomIn self self canvas set Map Tool self toolZoomIn Set the map tool to zoom out def zoomOut self self canvas setMapTool self toolZoomOut Set the map tool to def pan self self canvas set Map Tool self toolPan Zoom to full extent of layer def zoomFull self self canvas zoomFullExtent For each map tool we need a method that corresponds to the connection we made for each action In lines 79 through 88 we set up a method for each of the three tools that interact with the map When a tool is activated by clicking on it in the toolbar the corresponding method is called that tells the map canvas it is the active tool The active tool governs what happens when the mouse is clicked on the canvas The zoom to full extent tool isn t a map tool it does its job without requiring a click on the map When it is activated we call the zoomFullExtent method of the map canvas line 92 Quantum GIS FOSS4G2007 63 94 10 2 CREATING THE MAINWINDOW CHAPTER 10 CREATING APPLICATIONS
55. nd eM fey Eg Feature NAME CAPITAL N COUNTRY Canada NAME Victoria POPULATION 255547 Help The fields in the cities layer are displayed along with the corresponding value for each If you click among a cluster of features you may see more than one result in the dialog If you keep getting No features found when trying to identify a feature you can do one of two things or both e Zoom in and try again e Change the search radius used to find a feature Exercise 6 Changing the Search Radius To change the search radius choose Options from the Settings menu then click on the Map tools tab The search radius is specified as a percentage of the map width If you aren t able to click on a feature try increasing it to something like 0 7 If you find that too many features are being returned decrease the search radius 2 5 2 Using the Attribute Table To open the attribute table for a layer click on the tool The attribute table contains a row for each feature in your layer Quantum GIS FOSS4G2007 16 CHAPTER 2 GETTING STARTED 2 5 ATTRIBUTES AND ACTIONS Attribute table Cities aeeaa asa NAME COUNTRY Aden Yemen _ Adis Abeba 393 Agadez 208 Ahmadabad 178 Al Basra Al Kuwayt Al Madinah Aleppo Alexandria Algeria Australia Kazakhstan Indonesia 111914 Help Amman Jordan 1250000 172 Amritsar India Z
56. nerate the map file E E Quantum GIS FOSS4G2007 34 CHAPTER 5 MAKING MAPSERVER MAP FILES 5 3 TESTING THE MAP FILE Export to Mapserver lt 2 gt Map file home gsherman mapserver_test map QGIS project file home gsherman mapserver_test qgs Export cn information only Map Name My Test Map Width 600 Height 400 Units dd Image type png Web Interface Definition Template Header Footer Hep You ll notice there is no feedback on the success of your efforts This is an enhancement scheduled for the next version You can view the map file in an editor or using less If you take a look you ll notice that the export tool adds the metadata needed to enable our map file for WMS 5 3 Testing the Map File Let s test our work by using the shp2img command to create an image from the map file The shp2img utility is part of MapServer but is also distributed with FWTools To create an image from our map 1 Open a terminal window 2 If you didn t save your map file in your home directory change to the directory where you saved it 3 Run shp2img 4 View the created image Assuming our map file was named mapserver_test map the shp2img command is shp2img m mapserver_test map o mapserver_test png This creates a PNG for us to view containing all the layers that were on when we saved the QGIS project In addition the extent of the PNG will be the same as when we saved the project
57. nual for more details on the GRASS vector model and digitizing editing with QGIS With QGIS 0 8 and higher you can create an empty GRASS vector layer to use for digitizing features To create a new layer click the tool on the GRASS toolbar and enter a name for the new layer When you click ok the layer is created and the Grass Edit dialog opens ready for you to begin creating features By default the new layer contains only one field but you can add others using the tools on the Table tab 8 5 Using the Browser The GRASS browser allows you to perform a number of operations on your layers as well as get information about each To activate the browser open the Grass Toolbox and click on the Browser tab All of the mapsets in the current location are displayed on the left in a tree structure Typically you will see the PERMANENT mapset along with the one or more of your user mapsets If a mapset contains maps you will be able to expand the tree The maps are further categorized into raster region and vector nodes Expanding one of the nodes will show you a list of all the maps associated with it If you click on a map the pane on the right displays information about the map Quantum GIS FOSS4G2007 48 CHAPTER 8 GRASS AND QGIS 8 6 ANALYSIS GRASS Tools world geo gsherman Porou S s gsherman Vector E se raster pod ancc6_geo E E vector Lines Y BY ancc6_contour_100 Boundaries 0 0 Centroids 0 0
58. of the tabs Quantum GIS FOSS4G2007 11 Hint Use the scale display on the toolbar to help in setting scale dependency values 2 4 SYMBOLIZING YOUR DATA CHAPTER 2 GETTING STARTED Symbology Tab In addition to changing the band settings for the Red Green Blue and Alpha bands you can also do a number of things related to symbology 1 Change between color and grayscale 2 Invert the color map 3 Set the transparency for the raster 4 Adjust the settings for a grayscale image Be sure to read the image notes for information about your raster Tip 3 VIEWING A SINGLE BAND OF A MULTIBAND RASTER If you want to view a single band for example Red of a multiband image you might think you would set the Green and Blue bands to Not Set In version 0 8 1 this causes QGIS to crash To display the Red band set the image type to grayscale then select Red as the band to use for Gray General Tab The general tab allows you to 1 Change the name of the layer as it appears in the legend 2 Set scale dependency so the layer is only visible between and minimum and or maximum scale 3 View or change the spatial reference projection 4 View the thumbnail legend and palette graphics Typically you ll use this most frequently to change the display name and set scale depen dency Metadata Tab The Metadata tab provides more information than you would want to know about your raster including the size nu
59. ool You can select multiple features for deletion Once you have the selection set use the tool to delete the features There is no undo function but remember your layer isn t really changed until you stop editing and choose to save your changes So if you make a mistake you can always cancel the save The tool on the digitizing toolbar can also be used to delete features This effectively deletes the feature but also places it on a spatial clipboard So we cut the feature to delete We could then use the paste tool to put it back giving us a one level undo capability Cut copy and paste work on the currently selected features meaning we can operate on more than one at a time Quantum GIS FOSS4G2007 23 Ax Try It Try It Ax Try It Try It 3 2 EDITING YOUR FEATURES CHAPTER 3 DIGITIZING AND EDITING When would the copy and paste function come in handy Well it turns out that you can edit more than one layer at a time and copy paste features between layers Why would we want to do this Say we need to do some work on a new layer but only need one or two lakes not the 5 000 on our big_lakes layer We can create a new layer and use copy paste to plop the needed lakes into it Exercise 10 Copying Features Between Layers Try copying some of your lakes to a new layer 1 Load the layer you want to copy from source layer Load or create the layer you want to copy to target layer Start editing for both layers Make
60. own list and try it out Try loading the Users layer to the map You can identify features on the WMS layer depending on the capabilities implemented by the owner 6 1 2 Setting Options Depending on the service you can change the image format and the coordinate system when loading a layer First open the connection and click on the layer you want to load Then set the image type and projection from the available options 6 2 Using WFS Data In QGIS a WFS layer behaves pretty much like any other vector layer You can identify and select features and view the attribute table The WFS plugin doesn t support editing at this time Adding a WFS layer is very similar to the procedure used with WMS The difference is there are no default servers defined so we have to add our own Let s use the DM Solutions WFS server The URL is http www2 dmsolutions ca cgi bin mswfs_gmap VERSION 1 0 O amp SERVICE wf skREQUE GetCapabilities Quantum GIS FOSS4G2007 38 ST CHAPTER 6 CONSUMING WMS AND WES DATA 6 2 USING WFS DATA Exercise 15 Loading a WFS Layer To add the server and display a layer Make sure the WFS plugin is loaded if not open the Plugin Manager and load it Click on the tool on the plugins toolbar Click on Enter DM Solutions as the name Enter the URL see previous page Click Ok Choose DM Solutions from the drop down box Click Connect Wait for the list of layers to be pop
61. pand it and see the options available Choose one of the options by clicking on it Click to add it to the map Add Layer s from a Server Server Connections NASA JPL Connect Ne Delete Add default servers Image encoding JPEG PNG Layers ID y Name Title a global_mosaic WMS Global Mosaic pan sharpened pseudo default Pseudo color image pan sharpened U pseudo_low Pseudo color image pan sharpened Uses IR ani pseudo bright Pseudo color image Uses IR and Visual bands 5 5 visual Real color image pan sharpened Uses the visuchd Lal Coordinate Reference System 2 available WGS 84 Change Help Add Close Response is complete 37 xx Try It 6 2 USING WES DATA CHAPTER 6 CONSUMING WMS AND WFS DATA You can add additional layers by repeating the process 6 1 1 Adding a New WMS Connection You probably will want to use more WMS servers than the default set added by QGIS First you need to find the URL for the server Once you have the URL create a connection Let s create a connection to the QGIS WMS server 1 Click on the tool 2 Click the button 3 Give the connection a name we ll use QGIS WMS 1 Enter the URL Krr Taste org cgi bin mapserv nap var wuw naps nain nap 5 If a proxy is required enter the information for QGIS we don t need one 6 Click to create the connection You can now select the connection from the drop d
62. plugin adds a simple scale bar to the map canvas You control the style and placement as well as the labeling of the bar QGIS only supports displaying the scale in the same units as your map frame So if the units of your layers are in meters you can t create a scale bar in feet Likewise if you are using decimal degrees you can t create a scale bar to display distance in meters xxTry It To add a scale bar 1 Open the plugin dialog by clicking on the tool on the Plugins toolbar Choose the placement from the drop down list Choose the style Select the color for the bar or use the default black color Set the size of the bar and its label Make sure the Enable scale bar checkbox is checked Optionally choose to automatically snap to a round number when the canvas is resized Click oN o a RF ww Quantum GIS FOSS4G2007 30 CHAPTER 4 WORKING WITH PLUGINS 4 4 THE GPS PLUGIN Scale Bar Plugin Scale Bar Plugin This plugin draws a scale bar on the map Please note the size option below is a preferred size and may have to be altered by QGIS depending on the level of zoom The size is measured according to the map units specified in the project properties Placement Top Left Scale bar style Tick Down Size of bar 30 metres km y Enable scale bar y Automatically snap to round number on resize N OK Cancel 4 4 The GPS Plugin The GPS plugin allows you to upload an
63. put we ll use the QInputDialog class from the Qt library This prompts the user for a single line of input While it will make our plugin a little crude it serves to illustrate the concepts Quantum GIS FOSS4G2007 54 CHAPTER 9 PYTHON PLUGINS 9 5 CREATING THE PLUGIN All we need to write now is the Python code to collect the input and create the table 9 5 Creating the Plugin Now that we have the preliminaries out of the way we can get down to writing the code that does the actual work Let s start by looking at the things we need to import and the initialization of the plugin in newlayer py 1 Import the PyQt and QGIS libraries 2 from PyQt4 QtCore import 3 from PyQt4 QtGui import x 4 from qgis core import 5 import psycopg 6 Initialize Qt resources from file resources py 7 import resources 8 9 Our main class for the plugin 10 Class NewLayer 1 def _ init self iface 13 Save reference to the QGIS interface 14 self iface iface 16 def initGui self 17 Create action that will start plugin configuration 18 self action QAction QIcon plugins newlayer icon png 19 New PosGIS Layer self iface getMainWindow 20 QObject connect self action SIGN ALU activated self run 21 22 Add toolbar button and menu item 23 self iface addToolBarIcon self action 24 self iface addPluginMenu amp New PostGIS Layer self action 26 def unload self
64. s from the DEM 1 Open your mapset containing the layer Load the ancc6_geo raster layer Open the GRASS toolbox Find r contour under the Raster heading and click on it Make sure ancc6_geo is selected in the drop down box Click on the Use region of this map button to the right of the drop down box Enter the increment between contours we ll use 100 Enter a name for the output raster ancc6_contour Click Add the contour layer to the map and examine it E This created a contour map with 100 meter contour intervals We know this because the original DEM has elevations in meters Quantum GIS FOSS4G2007 50 CHAPTER 8 GRASS AND QGIS 8 6 ANALYSIS 8 6 3 Map Algebra The toolbox contains the Raster map calculator This allows you to create a model and run it to perform operations on each cell in a raster You could also use it to combine two rasters to create a third using simple addition or a more complicated operation or function Exercise 24 Using Map Algebra Let s use the calculator to convert our DEM from meters to feet CO N 10 11 12 Open your mapset containing the layer Load the ancc6_geo raster layer Open the GRASS toolbox Click on the Browser tab Find the ancc6_geo layer and click on it Click on the Set current region to selected map tool This constrains the raster processing to the region of our original DEM Click on the Modules
65. t a moment Using the same steps load the cities shp layer from the data directory Once you have the layers loaded take a look at the map navigation toolbar From left to right the tools are Pan pan the map by dragging the mouse Zoom In zoom in by dragging the mouse or clicking Zoom Out zoom out by dragging the mouse or clicking Zoom Full zoom to the full extent of all layers Zoom to Selection zoom to the extent of the selected features Zoom to Layer zoom to the extent of the active layer Zoom to Last Extent zoom to the previous view 8 Refresh redraw the map Feel free to experiment with the map navigation tools Tip 2 MISSING TOOLBARS If you find one or more of the toolbars are missing right click in the toolbar area to bring up the popup menu Click on the toolbars that you want to make visible 2 3 2 Viewing Raster Data Exercise 2 Loading the World Mosaic Raster Let s add the world_mosaic tif raster to our map 1 Click on the tool in the toolbar or choose Add a Raster Layer from the Layer menu Navigate to the data directory home qgisuser data qgis Make sure the Files of type drop down box has the GeoTIFF filter selected Choose world mosaic tif Click The raster is now loaded over your vector data You can rearrange the layers by clicking on them in the legend and dragging them to a new position in the stack Drag the cities layer to the top of the stack so t
66. t better To buffer the city labels 1 Click the Buffer tab 2 Click the Buffer Labels checkbox to enable buffering 3 Choose a size for the buffer using the spin box 4 Choose a color by clicking on and choosing your favorite from the color selector 5 Click to see if you like the changes If you aren t happy with the results tweak the settings and then test again by clicking o A buffer of 2 points seems to give a good result Notice you can also specify the buffer size in map units if that works out better for you The remaining tabs on the Label tab allow you control the appearance of the labels using attributes stored in the layer The Data tabs allow you to set all the parameters for the labels using fields in the layer Actions Tab We ll take a close look at Attribute Actions in the next section 2 5 Attributes and Actions QGIS provides several methods to view and work with the attributes of your vector data The simplest is the Identify function 2 5 1 Identifying Features To identify a feature on a layer 1 Make the layer active by clicking on its name in the legend 2 Click on the tool 3 Click on a feature Quantum GIS FOSS4G2007 15 2 5 ATTRIBUTES AND ACTIONS CHAPTER 2 GETTING STARTED xxTry lt Try this with the cities layer If you click on or close enough to a city you ll get a results dialog similar to this oe ae A A A A ES ae Pd ty Identify Results Cities 1featurefou
67. tab Find the r mapcalc module Create the model shown in the graphic below using the tools in the calculator Make sure you select ancc6_geo before adding the map to the model In addition to the map you need to add a constant 3 28 and a multiplication operator to the model Once the model is complete enter a name for the output raster Click to run the model Add the new raster to the map and examine it GRASS Tools world geo gsherman Modules Browser Module r mapcalc Options Output Manual Pirro Ex Output ancc6_feet Quantum GIS FOSS4G2007 51 8 7 SUMMARY CHAPTER 8 GRASS AND QGIS We used a very simple operation multiplication to create a new raster with cell values in feet You may have noticed a lot of functions available in the tool This gives you a lot of power to construct complicated models for raster processing 8 7 Summary Our look at QGIS GRASS integration just touched on the many options available to you Using QGIS to work with your GRASS data is a good way to get started using GRASS Many people have found that they soon are using GRASS outside of QGIS and being quite successful at performing complex operations and geoprocessing not yet supported by the toolbox Tip 9 LEARNING MORE ABOUT GRASS To learn more about GRASS and the commands available through the QGIS GRASS toolbox be sure to look at the Manual tab for each module as you use it Also be sure to
68. tab Remember the tolerance is in map units For our little digitizing project the units are in decimal degrees Your results may vary but something on the order of 0 05 to 0 1 should be fine 3 2 2 Editing Vertices Once the tolerance is set we can move vertices to correct mistakes and better match the shoreline Just click on the tool place the cursor over the vertex to be moved and drag it to the new location When you release the mouse the vertex is moved and the shape of the polygon changes If you find you missed some detail for example a straight line that missed a little inlet in the lake you can add one or more vertices to solve the problem First use the tool to add the vertices by clicking on the line segment that needs to be modified Don t worry if you don t get them exact Once you ve added the vertices you need use the move tool to adjust the positions to reflect the shoreline of the inlet If you didn t add enough vertices to accurately portray the feature no problem just add some more and move them around until the job is done You may find that you have too many vertices or just plain put one where it doesn t belong In that case use the tool to get rid of the ones you don t need When you delete a vertex the polygon reshapes itself automatically 3 2 3 Copy Cut and Paste What if we want to delete an entire polygon We can do that by first selecting the polygon in our example a lake using the regular t
69. taining the field names for the cities layer It s located just to the right of the button 9 From the drop down box select NAME and click 10 Your action text now looks like this firefox http google com search q NAME 11 Add a to the end of the action text 12 From the drop down list of fields select COUNTRY and click 13 Add the action to the list for this layer by clicking This completes the action and it is ready to use The final text of the action should look like this firefox http google com search q NAME COUNTRY We can now use the action Close the properties dialog and zoom in to an area of interest Make sure the cities layer is active and identify a city In the result box you ll now see that our action is visible iv identify Results Cities 1featurefound ESED x Feature CAPITAL N r COUNTRY Australia NAME Alice Springs POPULATION 99 action Google Search Help When we click on the action it brings up Firefox and navigates to the URL We could have just searched on NAME but then certain cities we choose might give us undesirable results without the coun try name TI leave those up to your imagination You can define multiple actions for a layer and each will show up in the Identify Results dialog You can also invoke actions from the attribute table by selecting a row and right clicking then choosing the action from the popup menu You can think of all kinds of uses
70. talling on Mac OS X and Windows these are bundled for you in the framework packages or the installer On Linux and other nix platforms you will need to install the dependencies prior to installing or building QGIS For distributions that have a package manager this is usually not a difficult task Its best to look around before building dependencies from scratch to see if packages or builds for your operating system are available A complete list of dependencies and build instructions for the current version can be found at http qgis org 68
71. the polygon radio button 3 Click and add the ID field with type Integer 4 Click and add the NAME field with type String When all set your dialog should look like this New Vector Layer EAE xi Point Line e Polygon File Format ESRI Shapefile Attributes Add Remove Name Type ID Integer NAME String Help Click to create the layer This opens the dialog to save the file allowing you to navigate to the directory where you want the shapefile to live and give it an appropriate name Our empty shapefile is created and displayed in QGIS To start digitizing we need to allow editing on the new layer by right clicking on it in the legend and choosing Allow editing from the popup menu A small pencil with a little scribble 21 3 2 EDITING YOUR FEATURES CHAPTER 3 DIGITIZING AND EDITING trailing from it appears over the layer s icon in the legend to indicate that we are now in edit mode Before we start editing we need to make sure the digitizing toolbar is visible If not right click in the toolbar area of QGIS and choose Digitizing from the popup menu Some of the buttons on the toolbar are disabled grayed out in particular the point and line buttons This is because QGIS knows we are editing a polygon layer and won t allow you to create the wrong feature type Exercise 9 Digitizing a Lake Let s start digitizing 1 Zoom in to an area on the world_mosaic wher
72. to fill your entire main window 00 10 Save the form as mainwindow ui An application created using Python and the QGIS bindings 60 o o s Oa A UU NY KF 23 27 CHAPTER 10 CREATING APPLICATIONS 10 2 CREATING THE MAINWINDOW 11 Exit Qt Designer Now compile the form using the PyQt interface compiler pyuic4 o mainwindow_ui py mainwindow ui This creates the Python source for the main window GUI Next we need to create the appli cation code to fill the blank slate with some tools we can use 10 2 Creating the MainWindow Now we are ready to write the MainWindow class that will do the real work Since it takes up quite a few lines we ll look at it in chunks starting with the import section and environment setup Loosely based on Original C Tutorial 2 by Tim Sutton ported to Python by Martin Dobias with enhancements by Gary Sherman for FOSS4G2007 Licensed under the terms of GNU GPL 2 from PyQt4 QtCore import x from PyQt4 QtGui import from qgis core import x from qgis gui import import sys import os A Import our GUI from mainwindow_ui import Ui_MainWindow Import our resources icons import resources Environment variable QGISHOME must be set to the 0 9 install directory before running this application qgis_prefix os getenv QGISHOME Some of this should look familiar from our plugin especially the PyQt4 and QGIS imports Some specific things to note are the
73. to load File home gsherman desktop_gis_data gps beach_lake gpx ie Feature types v Waypoints y Routes v Tracks 4 5 Graticule Creator The graticule creator lets us create a grid of points line or polygons to cover our area of interest All units must be entered in decimal degrees The output is a shapefile which can be projected on the fly to match your other data Exercise 12 Creating a Graticule To create a graticule 1 Make sure the plugin is loaded 2 Click on the tool on the plugins toolbar 3 Choose the type of graticule you which to create point line or polygon 4 Enter the latitude and longitude for the lower left and upper right corners of the gratic ule 5 Enter the interval to be used in constructing the grid You can enter different values for the X and Y directions longitude latitude 6 Choose the name and location of the shapefile to be created 7 Click to create the graticule and add it to the map canvas 4 6 Other Plugins We ll look at some of the other plugins later For those we don t cover feel free to explore them on your own Quantum GIS FOSS4G2007 32 Chapter 5 Making MapServer Map Files QGIS can be used to create map files for MapServer You use QGIS to compose your map by adding and arranging layers symbolizing them and customizing the colors In order to use the MapServer exporter you must have Python on your s
74. tures If you like import the world_borders shapefile into about 6 GRASS minutes to 8 3 2 Importing Rasters import the world borders The process for importing a raster is pretty much the same as for a vector layer First add it to the map then choose r in gdal module to do the import Let s import the DEM into our location Exercise 21 Importing a Raster DEM into GRASS 1 Make sure your mapset is open Open the GRASS toolbox If it s not active click on the Modules tab y Add the ancc6_geo DEM to QGIS Find the r in gdal module in the toolbox and click on it Choose ancc6_geo from the drop down list Enter ancc6_geo for the name of the output raster Click Click to add it to the map Close the GRASS toolbox Examine the new raster Quantum GIS FOSS4G2007 47 8 4 DIGITIZING AND EDITING CHAPTER 8 GRASS AND QGIS 8 4 Digitizing and Editing Editing of GRASS layers is done using the plugin You can edit both the features and their attributes using the tool To edit a layer activate it in the legend and then click the tool This brings up the GRASS Edit dialog GRASS Edit NOO0S 72H xn Elo Category Settings Symbology Table Mode Next not used Category 2 Field layer 1 Left Select element There are tools for creating the various feature types and editing the attribute table We won t go into detail about editing with GRASS see the QGIS user ma
75. ulated Click on the Canadian Land layer Click Add to add the layer to the map Wait patiently for the features to appear A EST NE E N eee y Note this plugin not considered stable yet Use it on yourown n PARME Ea Server Connections dm solutions Connect Ni Delete Title Name Abstract Canadian Land prov_land US Land land_fn Parks park US Lakes drain_fn Lakes drainage Provincial Borders prov bound Federal Limit fedlimit Milenario enil Coordinate Reference System Change Help X Cancel dd ox You ll notice there is no feedback while connecting to the server or while loading a layer Once the layer is loaded you can identify and select a province or two and view the attribute Try It table Remember this plugin is experimental you might also experience random behavior and crashes You can look forward to improvements in a future version of the plugin Tip 7 FINDING WMS AND WFS SERVERS You can find additional WMS and WFS servers by using Google or your favorite search engine There are a number of lists some of them maintained and some not that list public servers you can use Quantum GIS FOSS4G2007 39 Chapter 7 Viewing and Editing Data in PostGIS QGIS has had support for PostGIS from day one It was the first data store supported in version 0 0 1 Since then the support has evolved to inc
76. which we ll name resources qrc This is just a simple XML file that defines the icon resource lt RCC gt lt qresource prefix plugins newlayer gt lt file gt icon png lt file gt lt qresource gt lt RCC gt The resource file uses a prefix to prevent naming clashes with other plugins using the name of the plugin is usually sufficient The icon png file is is just a PNG image that will be used in the toolbar when the plugin is activated You can use any image as long as it s 22x22 pixels so it fits on the toolbar To turn the resource file into something the plugin can use it must be compiled using the PyQt resource compiler pyrcc4 o resources py resources qrc The o switch is used to specify the output file Now that we have resources we need a way to collect the information needed for creating a new layer 9 4 Creating the GUI Normally we would use the same tool that C developers use to create a GUI Qt Designer This is a visual design tool that allows you to create dialog and main windows by dragging and dropping widgets and defining their properties To design our NewLayer plugin we could get quite fancy and include widgets for field types and other options However since our time is limited we ll use another means to collect the information we need to create the table This will illustrate the concepts and then you can venture further using the tutorials on the QGIS blog To collect the user in
77. y interactively setting control points to create a world file Graticule Creator Create a graticule grid shapefile by specifying the extent and interval between latitude and longitude lines You can create a point line or polygon graticule with this plugin Launcher Launches a program or script from QGIS and captures the output Commands are stored in a drop down list for future use North Arrow Displays a customizable north arrow on the map canvas You can adjust the placement of the arrow as well as the angle Or you can just let QGIS determine the angle direction automatically PostgreSQL Geoprocessing Tools for processing PostGIS layers At present this plugin is rather limited and contains only a Buffer tool SPIT Shapefile to PostGIS Import Tool allows you to import shapefiles into PostGIS Scale Bar Displays a scale bar on the map canvas You can customize the placement style color and size of the scale bar WFS Experimental plugin for consuming WFS services on the Internet and displaying the 25 4 1 THE PLUGIN MANAGER CHAPTER 4 WORKING WITH PLUGINS data in QGIS This plugin is included as part of the QGIS package but at the time of this writing probably isn t ready for prime time 4 1 The Plugin Manager The Plugin Manager allows you to load and unload QGIS plugins Before you can use a plugin it must be loaded By default no plugins are loaded the first time you run QGIS Once you have loaded a plugin
78. ystem and QGIS must have been compiled with support for it 5 1 Creating the Project File To create a MapServer map file 1 Add your layers to QGIS 2 Symbolize your layers setting the renderer and colors 3 Arrange the layers in the order you want them to appear in MapServer 4 Save your work to a QGIS project file This gets us to the point where we are ready to create the map file Tip 6 MAPSERVER EXPORT REQUIRES A QGIS PROJECT FILE This has been a source of confusion for a number of people The MapServer export tool operates on a saved QGIS project file not the current contents of the map canvas and legend When using the tool you need to specify a QGIS project file as input 5 2 Creating the Map File The exporter tool msexport is installed in your QGIS binary directory and can be used independently of QGIS From QGIS you can start the exporter by choosing Export to MapServer Map from the File menu Here is a summary of the input fields Map file Enter the name for the map file to be created You can use the button at the right to browse for the directory where you want the map file created Qgis project file Enter the full path to the QGIS project file qgs you want to export You can use the button at the right to browse for the QGIS project file Map Name A name for the map This name is prefixed to all images generated by the mapserver 33 5 2 CREATING THE MAP FILE CHAPTER 5 MAKING MAPSERVER MAP

Shuffling Quantum GIS into the Open Source GIS Stack

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