Mirone: A multi-purpose tool for exploring grid data
Contents
1. Input Mag File Headers N ofheaders e 2 o l Compute Fig 5 Illustration of IGRF calculator Points for which geomagnetic field is to be computed can be selected by clicking on image Griding Line Geometry configures grid parameters necessary to compute a grid e g of total field or magnetic declination December 2004 by IAGA Working Group V MOD It is valid for dates 1900 0 to 2010 0 inclusive The IGRF routine a C mex file is also used within the Parker Directland tools The first allows the computation of the magnetic anomaly given a magnetization and bathymetry map using Parker s 1972 Fourier series Summation approach The second performs the inverse operation which is the computation of the magnetization from magnetic field and bathy metry Parker and Huestis 1974 This inversion procedure eliminates the dependency on the shape and amplitude of the magnetic anomalies with the distance between the survey altitude and the seafloor 5 4 Geographic calculator This tool is an interface to both the and grdproject programs in GMT It uses a mex version of these programs and its use is fairly straightforward GMT version 4 introduced datum conversions in but not in and shifts that allow conversion between the many projection systems in use Currently only the Portuguese systems are coded in Mirone Overall this tool frees GMT users from the need to provide a correct R for the tra2. 8 Example of settings used to generate a GMT shell script to plot contents of a Mirone window Rectangle which represents map s size can be dragged over page or have its limits altered Any of GMT map projections may be selected rivers and contour lines are not saved Instead appropriate calls to pscoast or grdcontour are inserted into the script 10 J F Luis Computers amp Geosciences E WIRE RIEAN 7 Evolution of Mirone Mirone is a powerful tool for displaying and analyzing grid and vector data loaded in a variety of formats The Mirone code comprises more than 90 000 lines of MATLAB code and about 30 000 of C mex code Due to its modular design careful programming and interface to GMT and GDAL libraries the program is able to read large amounts of data that would otherwise prove impossible if only MATLAB primitives had been used Currently however the GDAL and GMT links are weakly developed For example at the moment it is not possible to load any of the satellite image formats recognized by GDAL or to import ECW or MrSid wavelet based image compression technologies de veloped respectively by ERMapper and Lizard Tech compressed images Adding options to do these tasks is not technically difficult to program but great care will need to be taken owing to the potentially huge size of these types of image files uimenu Parent h278 Callback mirone GridToolsGridMas
3. SRTM mosaic tool showing four successful tile selections and error message displayed when intend SRTM tile could not be found in indicated directory 6 J F Luis Computers amp Geosciences E WIRE RIEAN 5 Discipline specific tools Mirone contains a range of specific tools for application to topics in geophysics and earth sciences The list of applications cover multi beam mission planning elastic deformation tsunami modeling including travel time estimation plate tectonic reconstructions Euler rotations and Euler poles computations magnetic field computations and magnetic inversions and seismicity and focal mechanism plotting A selection of these tools is discussed below 5 1 Elastic deformations The elastic deformation tools are accessible via the menu Here a line or polyline can be imported or drawn over the image grid The line is interpreted as the surface trace of a fault Right clicking on the line allows the user options to open new windows in which can be specified the fault parameters width depth dip as well as the movement deformation to be simulated The two available deformation options are called and Okada 1985 The tool is more general and can be used to simulate co seismic displacement that can be compared with GPS measurements for an initial condition of the far field tsunami modeling see below or to compute synthetic interferograms The window provides help in the form of tooltips when t
4. bathymetry grid Dark dots represent seismicity as imported from an ISC catalog Triangles correspond to active volcanoes Also two logo images were inserted to demonstrate this facility GMT program Rectangles may be used to limit the range of one operation to the area delimited by the rectangle The operation is quite common in many programs that display image type files In Mirone I have extended that concept to other operations It is thus possible to extract a sub region of a grid compute histograms and power spectrums determine autocorrelation apply median filters smooth by spline interpolation fill gaps holes in the grid set all grid nodes to a constant value and utilize a separate tool also included in the package to perform Region Of Interest ROI image processing type manipulations Furthermore the rectangle s limits may be used to register an image into another coordinate system The rectan gle corner coordinates are used to compute an affine transformation that registers the image to the rectangle s coordinate system The closed polygons also offer the possibility of measuring areas cropping grids and performing ROI manipulations The polygonal cropping differs from the rectangular one in that the grid nodes external to the polygon are set to not a number NaN Mirone contains a large collection of both general purpose operations and discipline specific modules Among the first group generally orga nized i
5. line 99 element either drawn or imported from an ascii file or point symbol may be rotated by using either a stage pole file as described above or a finite rotation pole When performing rotations with stage poles an age file that controls the ages for which the rotation is computed is required For each entry of that age file displayed in the window s listbox a new rotated line is plotted in the Mirone main window The button provides an easy way to select an age sequence using the geomagnetic polarity scale as reference If a single point is selected using the button instead of a line polyline then a single flow line is plotted In the Add poles tab the user may compute the pole that results from a combination of two finite rotations Users who desire to compute their own Euler poles can do this with the Geophysics gt compute Euler pole tool To use this tool two lines in the main window are mouse selected by depressing the button and an initial estimate of the Euler pole is entered The results of the search algorithm are graphically displayed every time a better fitting pole is found The process may be rerun using alternative initial estimates of the Euler pole if satisfactory results are not obtained with the initial estimate 6 3D view and printing Because Mirone does not use the 3D MATLAB functions the program does not offer any built in way of displaying graphics in 3D perspective Although MATLAB c
6. particular format as described in the rotconverter GMT program but example files can be found in Mirone s continents directory To create new stage poles files from finite rotations poles is clicked and the ensuing instructions followed The plates files are simple ascii files with two columns longitude and latitude The files may be multisegments with the character gt serving as the separator The individual segments may be closed in which case the contour is filled otherwise they are drawn as lines The first line in a file must take the form Name where Name is the plate s name This allows the program to associate a plate and its companion lines with a stage pole It also allows other elements e g the 3000m bathy metric contour to be added Mirone contains several other tools to manage plate movements For example under the menu the opens a window where the user can draw an arc circle about Euler poles representing the plate s present day movement Both relative and absolute plate movement options are available These arc circles also let the user compute the velocity vector magnitude and direction at any point along the circle This is a useful tool for discovering how one plate is moving relative to another at a certain point The rotation of magnetic isochrons and the creation of flow lines are accomplished using the tool in Geophysics gt euler rotations Any
7. the same number of rows and columns One of the grids represents the bathymetry z positive up in meters and the other contains the initial deformation as produced by the or deformation module A required parameter file swan par can be found in the data directory of the root Mirone installation which can be used as an example for other cases The user must choose between computing the simulation on specific points termed maregraphs here and or on the whole grid region If the first option is desired the stations can be plotted graphically using the option or the maregraphs locations can be imported in an x y file If the simulation is to be performed over the whole region then the option is used A new window called will popup where the final selections are made See the user s manual for further details on using this tool Okada deformation 19 O x Fault Geometry Dislocation Geometry Length Width Strike Rake Slip 56 660 42 4 Strike Dip ul u2 u3 12 4 450 EE En HZ Depth Depth to Top CONFIRM Sn Se S2 0 Geog S 0 67474 0 73805 0 Griding Line Geometry Min Max Spacing of lines Xx Direction 13 5 10 5 0 01 666666 181 Y Direction 39 5 41 5 0 01 666866 121 Hide fault plane Deformation C interferogram Input Ground Positions File Headers N8ofheaders 1 I Toge xy 2 Compute m Cancel Fig 4 Example of parameter settings used to
8. using imply double precision which takes twice as much memory When image files are being used however this rule does not apply Swath ratio When performing a multibeam planning the swath width coverage as a function of the water depth needs to be known When the first track is started by the user a question will be made concerning whether the current value is to be used or whether it should be changed Measure units When computing distances the result is presented in the chosen unit Available options are nautical miles kilometers meters and user defined Default ellipsoid Mirone computes distances on an ellipsoidal Earth The list of available ellipsoids include the 63 GMT supported ellipsoids plus one for Mars which is needed when working with MOLA grids Users that whish to set a custom ellipsoid will need to edit the mirone_prefs m file Working directory To reduce the cumbersome task of browsing through the directory tree every time a file needs to be saved the program uses a default working directory Either the full path may be typed here or the side button pressed to select a directory within a new window New grids in new window Many options involve the computation of a new grid This parameter controls whether the newly computed grid is automatically opened in a new Mirone window if this option is checked or saved on a disk file Force insitu transposition This option helps with the importat
9. would look something like without error checking function GridToolsFlipUD_Callback hObject eventdata handles retrieve the arrays stored in figure s appdata X Y Z head load_grd handles Flip the grid array Up Down Z flipud Z Save back the flipped array for future use setappdata handles figurel dem_z Z Get the image handle h_img findobj handles figurel Type image Flip also the displayed image set h_img CData flipdim get h_img CData 1 J F Luis Computers amp Geosciences D HHH iii 11 A final aspect of Mirone s evolution regards its portability to other operating systems In its current form despite the fact that it is written in MATLAB Mirone runs only in Windows This is a conse quence of using many compiled C mex files that are either self contained or make calls to the GDAL and GMT libraries To port Mirone to Unix Linux or Mac Os X all that must be done in principle is to recompile all such mex files under the specific OS Acknowledgements Maurice Tivey for giving permission to use his Parker inversion routines MATLAB contributors to file exchange from which many ideas were taken This paper and many improvements to the code were written during the author s sabbatical year This work was supported by the STRIPAREA POCI CTE GIN 59653 2004 project References Feigl K L Dupre E 1999 RNGCHN a program to cal
10. AS img GeoTIFF Grid Exchange File GXF from Geosoft Mars Orbiter Laser 4 J F Luis Computers amp Geosciences E WIRE RIEAN Altimeter MOLA grids and the common image formats When the loaded grid is referenced in geographical coordinates it is also possible to plot the netCDF coastlines database including rivers and political divisions provided by GMT These include not only the coastlines themselves but also the rivers and political divisions country frontiers and US states The netCDF coastlines database is the only currently available non ASCII vector format Other line and point data must be loaded from ASCII disk files containing x y coordinates one record per line Multi segment files that is a file where segments are separated by a special record the gt character are also supported When a grid is loaded the Mirone window expands to accommodate the image derived from the grid At the bottom of the window the current mouse position is displayed in the grid s coordi nates Clicking and dragging over the image shows the distance in the selected user units The generated image uses a default color map but more than 100 other color palettes are available by clicking on the palette icon button to access the palette tool not Shown here All palettes may be changed by a double click over the color bar This inserts color markers which can be dragged to modify the color map A second double click deletes th
11. COMPUTERS GEOSCIENCES Computers amp Geosciences E HEHE HiI HHE www elsevier com locate cageo Mirone A multi purpose tool for exploring grid data J F Luis CIMA Universidade do Algarve Campus de Gambelas 8000 117 Faro Portugal Received 15 October 2005 received in revised form 5 May 2006 accepted 26 May 2006 Abstract Mirone is a Windows MATLAB based framework tool developed by the author that allows the display and manipulation of a large number of grid formats through its interface with the Geospatial Data Abstraction Library GDAL Its main purpose is to provide users with an easy to use graphical interface to the more popular programs of the Generic Mapping Tools GMT package In addition it offers a range of tools dedicated to topics in the earth sciences including tools for multibeam mission planning elastic deformation studies tsunami propagation modeling earth magnetic field computations and magnetic Parker inversions Euler rotations and poles computations plate tectonic reconstructions and seismicity and focal mechanism plotting The high quality mapping and cartographic capabilities for which GMT is renowned is guaranteed through Mirone s ability to automatically generate GMT cshell scripts and dos batch files User specific requirements that lie outside the current capabilities of Mirone can be met by simple programming to provide the required functionality 2006 Elsevier Ltd All rights
12. TM tiles can be drawn A mouse click on each individual quad rangle searches the previously selected working directory for existing SRTM files The square turns red if the matching file exists if it does not exist a warning message is displayed and the square returns to yellow The size of raster datasets grows very quickly For example the General Bathymetric Chart of the Oceans GEBCO min resolution grid contains 445 Mb of data but the global mosaic of the SRTM tiles amounts to 1 9Gb in GeoTIFF DEM format This means that the majority of computers owned by typical users will probably not be able to process those files at their full resolutions One way to circumvent this problem as used by some soft ware packages is to use complicated algorithms that split the entire dataset if the data format allows them to in layers of variable resolution Mirone approaches the problem of loading data from very large grids somewhat differently With the the user may inspect the contents of a very large grid without loading it What this tool actually does is to read n other rows and columns in order to obtain an overview grid that is as close as possible to 200 x 200 rows and columns and builds a pre view image The user can then draw a rectangu lar area in order to extract the data at its full resolution SRTM Tool 14 12 Zoom On Ott Draw rectangle The file N36W010 hgt does not exist in the current directory Fig 3
13. an display in 3D by using its surface primitive this consumes a lot of memory and has poor interactive response As an alternative Mirone uses the IVS Fledermaus free 1View3D viewer www ivs unb ca products iview3d Fleder maus is a fast powerful 3D visualization tool capable of viewing large amounts of data Fig 7 Translations rotations and scaling are accom plished by simple mouse controls For launching the 3D view all is need is to hit the button with the eye icon By launching the 3D view via the eye icon Fig 2 a temporary fledermaus object sd file is created and used as an argument for the 1View3D call As an alternative the user may choose to save the fledermaus object in and later im port that object directly from the viewer Saving the Muirone display can be achieved in three ways The first is through J F Luis Computers amp Geosciences D WIRE Hii ill 9 iView3D D mirone_devel tmp lixoSD sd Fig 7 3D view of a bathymetry grid using Fledermaus free 1View3D viewer Light gray cubes represent seismic events There are more epicenters represented but they are hidden behind current figure display Changing viewpoint with mouse controls will show them White line represents coastlines extracted from GMT coastlines database File gt Save Image As which saves the current display image into one of the common image formats but without including any graphic elements e g lines symb
14. characterize movement along a fault and to compute elastic deformation produced by that movement J F Luis Computers amp Geosciences E HHH UHHH 7 5 3 IGRF calculator The International Geomagnetic Georeference Field IGRF calculator Fig 5 is a tool that computes the value of the total magnetic field or its components for given points A single point can be selected either by a mouse click on the world map or by entering its exact coordinates Alternatively a file can be read and imported that contains the magnetic data along with longitude and latitude positions The user has the option of choosing to compute the magnetic anomaly measured total field minus the IGRF magnitude Computing the magnetic anomaly requires knowing the date of data acquisition in which case the file reading function has the ability to decode many date formats including text formats The IGRF model used is the 10th generation IGRF as agreed in 3 IGRF Calculator 50 150 100 50 0 50 100 150 Location Latitude 28 deg 10 min 58 58 sec 28 183 Decimal Longitude 125 deg 47 min 2 86 sec 125 784 Decimal Elevation 0 m Date d m yyw 19 3 2006 2006 213 Decimal Point values Total Field 45826 nT Inc 40 9 Dec 49 X 346507 nT Y 2969nT Z 30008 nT H 34635 nT Griding Line Geometry Min of lines Max Spacing X Direction 180 180 1 361 Total field Y Direction 89 89 1 179 Compute
15. culate displacement components from dislocations in an elastic half space with applications for modeling geodetic measurements of crustal deformation Computers amp Geosciences 25 6 695 704 Imamura F 1997 Numerical Method of Tsunami Numerical Simulation with Leap Frog Scheme Time Project IUGG IOC UNESCO Paris Madder 2004 Numerical Modeling of Water Waves Second ed CRC Press Boca Raton FL 288pp Okada Y 1985 Surface deformation to shear and tensile faults in a half space Bulletin of the Seismological Society of America 75 4 1135 1154 Parker R L 1972 The rapid calculation of potential anomalies Geophysical Journal of the Royal Astronomical Society 31 447 455 Parker R L Huestis S P 1974 The inversion of magnetic anomalies in the presence of topography Journal of Geophysical Research 79 1587 1593 Wessel P Smith W H F 1991 Free software helps map and display data EOS Transactions of the American Geophysical Union 72 41 441
16. e marker The and fields may be used to impose a fixed color map between those values External GMT color palettes may also be imported or exported via the menu Another common operation is to show patterns and fine details in the grid image as revealed by applying a shading illumination Mirone offers five different algorithms for shading illuminations By default a mex version of the GMT program is used to do this but the user can select any of the five methods from within the control window Sun azimuth and elevation when accepted by the method are controlled with the mouse The buttons with T circle line rectangle closed polygon and arrow icons permit the user to draw any of these graphical elements Fig 2 Those elements may be subsequently edited by double clicking the selected target Besides their use as simple drawings which may be saved as ascii files such elements in particular the polylines rectan gles and closed polygons allow other possibilities A polyline for example may be used to measure the distance or azimuths of its individual segments and it can be also used to extract and show a savable grid profile in much the same way as the PROTAG AT melee Disine a DUilec nN ne i 10 x File image Tools Oraw Datasets Geophysics Grid Tools Heb OG OFS TOLSOGAQMLGA BAPE Sh Velocity 0 42 cmyr Azimuth 72 degrees Fig 2 Example case base image was computing by shading illumination of a GMT
17. ecific needs of those who regularly use gridded data but is particularly focused on the fields of geophysics and earth sciences It provides compre hensive data visualization and analysis in a user friendly environment One of Mirone s advantages is that the author is also a user I have found that much graphically oriented software obliges the user to follow a strict procedure that often requires in depth study of the accompanying manual in order to accomplish even simple display tasks In Mirone the user merely loads the grid of interest assuming that it belongs to one of the recognized formats and views it Particular atten tion has been paid in the program to offer the user the simpler and more often used options first and to let the more specific options show up only when they may be needed to solve a particular problem Since Mirone offers a large number of operations it has been designed in a modular fashion Options that require input parameters are run from inde pendent windows which whenever possible offer clever default values A comprehensive set of tooltips and helps has been attributed to the buttons and boxes where data have to be entered in order to facilitate the comprehension of each module s operation to the extent that many modules should not require reference to the manual The modular design can be explored further by users with programming skills and it is relatively easy to add new p
18. gorithm recommended by the United Nations Convention for the Law Of Sea UNCLOS to be used in the determination of the Foot Of continental Slope FOS The SRTM has obtained elevation data over most of the globe to generate the most complete high resolution digital topographic database of the planet It is distributed as 1 DTM tiles of 1 arcsec for the US territories and 3 arcsecs for the rest of the world between 56 S and 60 N In areas of high relief areas covered by water e g rivers dams and natural lakes and at land ocean transitions the SRTM models commonly display zones of no data grid holes Although strategies to fill these holes using coarser data e g from the elevation data model GTOPO30 could potentially be used the coarser resolution may not depict such areas with sufficient accuracy Therefore the Mirone solution is simply to offer the user the possibility to fill the holes which are automatically detected in Mirone by either minimum curvature or bilinear interpola tion The resulting processed file may be saved in the SRTM format Given the limited coverage 1 x 1 of each individual SRTM tile it is often desirable to be able to create mosaics Mirone has a dedicated and easy to use tool to accomplish this task Fig 3 With the SRTM mosaic tool the user first draws a rectangle to define the ROI By right clicking on the rectangle and choosing mesh yellow quadrangles corresponding to possible SR
19. he mouse rests over individual entry boxes For a complete reference to the use of the window the user should read the RNGCHN program paper Feigl and Dupre 1999 In that original paper the RNGCHN code is provided both as a stand alone FORTRAN code and as a MATLAB FOR TRAN77 mex file The stand alone code depends on some C code to deal with input output but it is system dependent it runs only on Sun and HP UNIX systems The mex file because it is written in F77 has the limitation of not supporting dynamic memory allocation Mirone uses a C version in which coordinate conversion routines were added The option computes only the vertical component of the deformation produced by an earthquake The two codes should produce equal results and trials show this to be the case In both and Mansinhal all distances are computed by projecting the geographical coordinates to Transverse Mercator with the origin being the fault s first point Fig 4 presents an example of using Okadal 5 2 Tsunami modeling Mirone has two codes to perform tsunami modeling of propagation and inundation The SWAN code Madder 2004 Mader Consulting Co and the TUNAMI N2 code Imamura 1997 Both of these codes were converted from FOR TRAN to C to allow dynamic memory allocation The example presented here uses the SWAN code To use this program the user needs to have two grids that are exactly compatible i e they must cover the same region and have
20. ion of large grids Importing grids involves a conversion that uses matrix transposi tion which requires twice the grid size in memory when a copy is made of the grid to speed importa tion The in situ transposition option uses only the grid size in memory and should be used where the computer has insufficient memory although the importation runs about 10 times more slowly than if the grid is copied When possible save as int16 Some grids use short ints 2 bytes to save disk space Checking this option means that if the grid is saved in the GMT format the 2 bytes original density will be retained otherwise it will be saved as floats of 4 bytes This is useful for example to convert Shuttle Radar Topography Mission SRTM grids into GMT format Default line thickness This default value is used for drawing lines circles or other graphical ele ments Default line color This default value is used for drawing lines circles or other graphical elements such as text strings For a complete explanation of all options offered by the program the reader is directed to the user s manual 4 General functionality By default Mirone automatically detects and reads all types of netCDF GMT grids as well as Surfer 6 and 7 grids Many of the formats recognized by GDAL may also be accessed through the menu Those include GeoTIFF DEM DTED USGS DEM USGS SDTS DEM Gto po30 SRTM DEM Arc Info ascii binary grids ENVI ERD
21. itude and latitude otherwise select Cartesian This is an important setting because some operations such as measuring depend on the grid coordinate system Grid Max size In order to perform grid manip ulations Mirone stores the original grid in the computer s memory in single precision This is the maximum size in Mb that a grid can occupy in the computer s memory This does not mean that larger erids images cannot be processed it means that if they exceed the size value they will be re read from disk as required The user must decide a reasonable value for this parameter based on the capabilities of J F Luis Computers amp Geosciences 0 WIRE iil 3 mirone_pref Use new GMT netCDF arid format Peles Grid coordinates 300 Grid max size Mb 1 5 Swath ratio Geographic C Cartesian Measure units nautic miles WGS 84 1984 Default ellipsoid Default directory IC iMbat tejo z MV New grids in new window Force Insitu transposition lv When possible save as Intl6 Default line thickness Default line color 2 pt z Black z OK Cancel Fig 1 Parameter configuration window the computer being used Grid size is computed as n_rows x n_columns x 4 1024 x 1024 Note Mir one makes most of its heavy computation using external mex files that use scalar single and double precision arithmetic However some operations may be performed with MATLAB operators
22. k_ Callback gcbo guidata gcbo GMT itself continues to evolve The developing version 5 will be significantly different from previous versions although backward compatible It will be reborn as a true code library that programmers will be able to use with little wrapping code in order to access its full capabilities P Wessel pers commun April 15 2005 A MATLAB compatibility layer is also planned at which stage Mirone will be able to more fully explore GMT s capacities A full range of map projections will also be added In the meantime adding new options is a relatively straightforward task I give a simple example on how Mirone can be extended to perform another operation in this case to add a menu entry that allows a grid to be flipped upside down The first step is to decide where the new entry will be added in the menu after the option is appropriate The menus are declared in the mirone_uis m file Searching this file for reveals lines that read Label Write Mask Tag GridToolsGridMask A new uimenu call and a new callback name function are declared here denoted GridToolsFlipUD_Call back uimenu Parent h278 Callback mirone GridToolsFlipUD_Callback gcbo guidata gcbo Label Flip Up Down Tag GridToolsFlipUD Now a new callback function is added to the mirone m file and programmed It
23. ment The language is easy to learn and contains a large collection of mathematical func tions that facilitate the task of writing complicated code including Graphical Users Interfaces GUIs p J F Luis Computers amp Geosciences 0 WIRE RIEAN However it also has limitations including those of speed and memory consumption In order to circumvent these constraints almost all substantial computations involving matrix data in Mirone have been made with the help of external code written in C and compiled as mex files Because the mex files use scalar programming and employ single precision or short integer variables in circumstances where accuracy is not compromised their memory con sumption is reduced to the minimum necessary whilst the running speed is that of a compiled code This paper reports the general characteristics of Mirone and describes and explains the program s main capabilities and functions The paper also provides some example applications to topics in the earth sciences including elastic deformation tsuna mis and plate tectonic motions Aspects of the future refinement and development of Mirone are also addressed including an example of how it can be extended by programming for particular needs The source code and a stand alone version which is a version that does not require MATLAB are available at w3 ualg pt jluis mirone 2 The program design philosophy Mirone was designed to address many of the sp
24. nsformation potentially particular hard to know in advance in inverse transformations a problem which has prevented many users from being able to use grdproject 5 5 Plate reconstructions This tool lies somewhere between a plate recon struction demonstration and an application that can be used to do advanced plate motion work There are some dedicated software packages available on the web that perform plate reconstructions see for example www geodynamics no gmap ngu gmap Geodynamics htm and links therein However the Mirone plate reconstructions tool is easy to use and has good functionality Options can be obtained by right clicking over the plates New menus pop up see Fig 6 from which the user can control how the plates move By default the program associates a movement history to three plates Iberia Eurasia and Africa The movement is defined by the poles as displayed in the window s bottom left corner In addition to the default files the user can load his her own data including poles files and plates files 8 J F Luis Computers amp Geosciences E WIRE RIEAN 3 Rally Plater A 10 x rs Fig 6 Pate reconstruction tool Reconstructions for particular times are performed using time slider Example shows position of Iberia Eurasia and Africa relative to a fixed North America at 90 Ma ago The poles used in this program are stage poles not finite rotation poles They have a
25. nside the menu the user may find interactive tools to drive a selection of GMT programs namely Grdfilter filters grids in the time domain using one of the selected convolution or non convolution filters J F Luis Computers amp Geosciences D WIRE iii 5 Grdgradient computes the directional deri vative in a given direction or the direction and the magnitude of the vector gradient of the data Grdproject transforms a gridded data set from a rectangular coordinate system into a geographical system or vice versa by resampling the surface at the new nodes Grdsample teinterpolates and creates a new grid with either a different registration or a new grid spacing or number of nodes and perhaps also a new sub region Interpolation is bicubic or bilinear and uses boundary conditions Grdtrend fits a low order polynomial trend to the grid of interest using optionally weighted least squares Surface and nearneighbor interpolates random ly space triplets x y z into a regular matrix that can later be saved as a GMT grid Other options involve computing histograms clipping a grid above and or below selected planes writing a mask grid where non NaN values are replaced by the number 1 computing spectra and autocorrelations smoothing grids by spline inter polation computing slope aspect and directional derivatives and computing a Second Derivative in the direction of Gradient SDG The SDG is the al
26. ols The second way through saves both the image and all elements that may have been added to it in a screen capture A third possibility involves generat ing a GMT cshell script or dos batch file The opens a window Fig 8 in which it is possible to fine tune map details such as size position on the page and projection system used This tool searches all elements in the display and decides the best way to reproduce the display using only GMT commands For example if the image displayed is derived from a GMT grid illuminated with a shading method from lgrdgradient the script lines will generate an illumination grid from the original GMT grid and use grdimage with the I option If that is not the case then a screen capture is executed and the image saved as three R G and B grids The three grids are then utilized by grdimage to rebuild a color image Line elements are written on disk and used by psxy However coastlines national borders Write GMT batch Map projection 20 System gt Projection gt Mercator Greenwich and Equator as origin 15 Elipsoide gt WGS 84 J lt options gt gt JM0 0 15 00c 10 D mirone_devel z f 5 Name prefix mir19 3 Map scale apr 1 5937040 ar a e A Map width 15 00 A4 2099 29 70 wake aes l cm vv x origin 25 com Cin C pt Update Y origin 25 Portrait Set map width C Landscape Set map height Saar Write batch Fig
27. ossibilities to the main program as demonstrated in Section 7 below For the purposes of demonstration or teaching a number of datasets have been incorporated covering topics such as seismicity active volcanoes ODP DSDP sites plate boundaries major cities and magnetic isochrons of the world s oceans These datasets are not purely static but contain relevant information associated with various items For example right clicking on a plate boundary segment informs the user about neighboring plates as well as the opening rate and direction 3 Starting the program Upon starting the user is presented with Mirone in its basic form which is a simple bar containing various menus See Fig 2 for an example of a Mirone window with data already displayed Activities are initiated by using these menus Although Mirone has pre defined defaults it is very important that the user understand what these defaults mean and do The first time the program is used the user is strongly advised to press the button with hammers icon This icon opens the preferences window Fig 1 The meanings of those settings are Use new GMT neiCDF grid formar Starting with GMT version 4 1 a new type of COARS compliant GMT net CDF grids was introduced While this change is transparent to users the new grid format will not be recognized by previous GMT versions Grid coordinates Select Geographic default if working with a grid whose coordinates are long
28. reserved Keywords Mirone GMT Data conversion Grids Geomagnetism Plate tectonics Geophysics 1 Introduction Mirone is an open source code written in MATLAB 6 5 by the author and has been developed specifically for the purpose of visualizing and manipulating GMT netCDF grids GMT Wessel and Smith 1991 is one of the most popular programs within the scientific community on account of its mapping capabilities and high quality graphics However most commercial software packages ignore this format and products that are able to read GMT and to display and manipulate Code available from server at http w3 ualg pt jluis mirone Tel 351 289 800938 fax 351 289 818353 E mail address jluis Qualg pt 0098 3004 see front matter 2006 Elsevier Ltd All rights reserved doi 10 1016 j cageo 2006 05 005 GMT grids are rare An additional problem that users face concerns data format There are presently tens of different formats for storing gridded data and imagery data and accessing data from dis parate sources is a common problem Murone minimizes this obstacle through its interface with the GDAL www gdal org GDAL is a unifying C C API for accessing raster geospatial data released under the MIT Open Source license which aims to provide efficient access suitable for use in viewer applications and which attempts to preserve coordinate systems and metadata MATLAB is a powerful tool for software develop
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