ActivGeoCalib User`s Manual
Contents
1. i The Results of Calibrating Name Thickness 7 38 vium J 7 40 vj um 13 20 mm J Telecentric Image List 1 Refeencelnage H A Grab Delete z Calibration Pixel Size 3246 511 um Distance 1469 cm Pan 061 Deg Rotation 313 neal Slant 4330 Deg Unit m z Delete All 2 T oO O oO lt click Calibrate to start the calibration save the calibration data the results are displayed automatically if you select another reference image a recalibration is performed Figure 2 3 The actual calibration process the appearing file selection box In the other project load the data via clicking Load If you now select another image as the reference image the system is recalibrated auto matically ActivVisionTools 3 2 Your Fast Track to Solutions 16 Using ActivGeoCalib ActivGeoCalib 2008 04 23 Chapter 3 Combining ActivGeoCalib with other ActivVisionTools This chapter will explain how other ActivVisionTools use the extracted calibration information to convert their results to 3D In the corresponding example Visual Basic projects ActivMeasure is used to measure the dis tance of markings on a calliper rule Please consult the User s Manual for ActivMeasure for detailed information 3 1 Converting Results of other ActivVisionTools 18 3 2 Ac2. 30mm 100mm 200mm To calibrate your vision system you just need to grab images of the calibration plate in different positions and orientations ActivGeoCalib will do the rest Note that we recommend to use the new calibration plates with the triangular mark see figure 1 1 because their orientation can be determined uniquely You can upgrade an old plate by painting a triangle in one of its corners yourself Please note that the calibration plates are not included in the ActivGeoCalib package you can order them from your local distributor Which calibration plate is suited best depends on your ActivGeoCalib 2008 04 23 1 1 Introducing ActivGeoCalib 3 Figure 1 1 Two of the calibration plates 30mm new with triangular mark and 10mm old without mark machine vision task As a rule of thumb if you grab an image of the plate in the plane of measurement it should fill a large part of the image For example if an image of the plane of measurement corresponds to an area of 80mm x 60mm as in figure 1 1 you should choose the 30mm calibration plate 2 T oO O oO lt The bigger calibration plates 100mm and 200mm made from aluminium come together with a file containing their exact measurements caltab_100mm descr and caltab_200mm descr Please copy this file to the subdirectory calib of the HALCON base directory you chose during installation default C Program Files MVTec Halcon The files for th
3. Noise Level Select tf gt i Rowidth favTMeasuel gt roi f Standard z Accuracy Object a Width Distance Center Distance Pair Row Center Column Edge Feature Selection 0 0 383 4 971 4 600 3 101 0 135 I Positions I Angles CH 0 360 5 008 4 654 4 130 0197 dua moce OR 0 348 4 980 4 646 0 878 0 260 i 3 0320 4 997 4 671 5 857 0 324 I Amplitudes ec 0 333 10 854 0 390 Pair Widths J Pair Width deat 4 5 Vv ie Centers L 5i Enter Ang IZ Enable Update ea JV Pair Center Distances f Pair Center Ang G the results are automatically converted into the selected unit select a unit Figure 3 1 Converting the results of ActivMeasure into millimeters ActivVisionTools 3 2 Your Fast Track to Solutions 20 Combining ActivGeoCalib with other ActivVisionTools 3 2 ActivGeoCalib vs AVTViewCalibration As described in section 1 1 on page 2 Activ View contains a support tool called AVTViewCali bration which provides a fast 2D calibration In this section we compare the results of the two calibration tools As in the previous section the example task is to measure the distance between the markings on a calliper rule isual Basi ies Preparation for the following example Example If you worked on the previous example you may continue using this project At design time add AVTViewCalibration and AVTViewROI to the form by double clicking the icons Fl and 4 Otherwise open the pro
4. Track to Solutions 2 T oO O oO lt 14 Using ActivGeoCalib Visual Basic Example 2 3 Calibrating As described in section 1 1 on page 2 the calibration results correspond to a so called reference frame which describes the plane in which measurements of other ActivVisionTools take place You can specify this reference frame very easily by selecting one of the calibration images which is then called the reference image Preparation for the following example If you worked on the previous example you may continue using this project Otherwise open the project results geocalib_results vbp and execute it Run gt Start or via the corresponding button Select the image sequence calib calib_3cm_1 seq and load its 12 images for the calibration by clicking Grab twelve times in AVTGeoCalibration The following steps are visualized in figure 2 3 D Select a reference image with the slider Reference Image or by typing its number in the neighboring text field in figure 2 3 the first image of the sequence was selected Specify the distance between the surface of the calibration plate and the desired plane of measurement in the text field Thickness If e g the calibration plate lies directly on top of the plane of measurement in the reference image this distance corresponds to the thickness of the calibration plate itself default value In the example in figur
5. shows up in the results of AVTViewCali bration For comparison now load the the calibration data file calib_3cm_1 cal which cor responds to the image sequence calib calib_3cm_1 seq As you see the distances between the centers of the pairs are now almost equal ActivGeoCalib 2008 04 23 3 2 ActivGeoCalib vs AVTViewCalibration 21 select a unit and enter the length of your line the results are converted automatically select AVTViewCalibration1 and draw a line shaped ROI over the markings 2 2 Pal ef 2 21 Copy Paste Delete _Deltean ActivVisionT ool ANTViewCalibration1 he Region of Interest Line_2 WAN l 21 Locked Unit mm Length Line f 0 00 1 Pixel Height foa 07527 mm User Defined N 2 T oO O oO 2 lt iix Light Park gt Edge Type era wa ans at ans Pa Ro Ci a Jesse Pais gt Edge Grouping 0 335 4 456 4 P aledges z 0 330 4 700 A i H ges Edge Selection oath l sf gt 15 Edge stenath a B44 71 3987 SI f gt E Noise Level fA Fit Rowidh Standard gt Accuracy 74 0 0 383 4 971 4 600 3 101 0 135 1 0 360 5 008 4 654 4130 0197 2 0 348 4 980 4 646 0 978 0 260 3 0 320 4 997 4 671 5 857 0 324 A a DIII sa es a 0 390 4 gt G to compare load a 3D calibration data file Figure 3 2 Comparing AVTViewCalibration and ActivGe
6. want to measure parts which are transported on a conveyor belt place the calibration plate directly on the conveyor belt Then you select this image as the reference image Furthermore you can specify an offset between the top of the calibration plate and the plane of measurement if you place the plate directly on top of the object you want to measure this offset is equal to the thickness of the plate itself The origin of the plane of measurement lies in the center of the calibration plate ActivVisionTools 3 2 Your Fast Track to Solutions 6 About ActivGeoCalib The Different Types of Lenses Using ActivGeoCalib you can calibrate both standard lenses and telecentric lenses Standard lenses are similar to those in the human eye They perform a perspective projection this means that objects become smaller in the image the farther they are away from the camera In contrast telecentric lenses perform a parallel projection Therefore objects have the same size in the image independent of their distance to the camera This means that they can lie in different planes only the orientation of the planes relative to the camera must be identical ActivGeoCalib vs AVTViewCalibration Besides ActivGeoCalib the ActivVisionTools family includes a second tool for converting re sults from pixels to other units ActivView s support tool AVITViewCalibration It offers a quick but rough calibration mechanism The user draws a line on the imag
7. world coordinates Note however that the origin of the world coordinates is placed in the upper left corner of the image The world coordinates of the upper left corner ActivGeoCalib 2008 04 23 4 2 Rectifying Images for Other ActivVisionTools 27 pixel can be queried with the properties Calibration RectificationX and Calibra tion RectificationY of the first instance of AVTView For more information about modifying images during the execution cycle of ActivVisionTools please refer to the Advanced User s Guide for ActivVisionTools section 3 4 2 on page 73 ActivVisionTools 3 2 Your Fast Track to Solutions 2 8 8 e 0 iS lt
8. For example the extent features based on the surrounding rectangle become inexact because the blobs don t appear as rectangles in the original image For moment features no 3D transformation is performed at all Currently images can only be rectified via the programming interface of Activ VisionTools We recommend to use the following approach Add a second instance of AVTView to the form At run time set its mode to Use Locally Stored Image in Properties see the Advanced User s Guide for ActivVisionTools section 3 6 1 3 on page 96 Switch on slave execution via the check box v Execute Slaves of AVTViewExecute also see the Advanced User s Guide for Activ VisionTools figure 3 12 on page 90 At design time add the following code Private Sub AVIView1_ImageGrabbed hImage As HALCONXLib IHUntypedObjectX _ ByVal lError As Long Set AVTView2 HalconImage _ AVTView1 Calibration RectifyImage AVIView1 HalconImage Call AVTView2 Calibration SetSimpleGeomCalib AVTView1 Calibration RectificationSize End Sub Then all grabbed images are automatically rectified and passed to the second instance of AVTView Furthermore the calibration information of the second AVTView is adapted such that the pixels have the correct size Connect other ActivVisionTools that are to process the rectified image to the second in stance of AVTView using AVTViewConnections Their features are automatically cal culated in
9. R Oe ee a 10 2 2 Grabbing Images of the Calibration Plate 6 12 23 Calibrating lt s occ ck a eee Se eee Ce Hew ewes 14 2 8 e o 0 im lt 10 Using ActivGeoCalib Visual Basic Example 2 1 Getting Started with lt Before we start with the actual calibration process two things should be done First you need to extract some parameters from the datasheets of your vision system Secondly when using live images from your vision system you need to open the connection to your image acquisition device Preparation for the following example Open the project start geocalib_start vbp Alternatively create a new project and place AVTView AVTViewFG AVTViewStatus and AVTGeoCalibration to the form by double clicking the icons i a Ai and lt respectively with the left mouse button Execute the application Run gt Start or via the corresponding button The following steps are visualized in figure 2 1 First of all select the description file of the calibration plate you are using in the combo box Name or via the file selection dialog If you want to experiment with the calibration image sequence calib calib_3cm_1 seq select caltab_30mm descr In the datasheet of your camera look up the cell size and enter the values in the text fields Cell Size X and Cell Size Y The value for the field Focal Length can typically be
10. User s Manual AcTrid SEOCALIB Your Door into the 3D World Microsoft Windows Windows NT Windows 2000 Windows XP Visual Basic Microsoft NET Visual C Visual C and ActiveX are either trademarks or registered trademarks of Microsoft Corporation All other nationally and internationally recognized trademarks and tradenames are hereby rec ognized EC Copyright 2001 2008 by MVTec Software GmbH M nchen Germany _mvreeseftware cmb Edition 1 February 2001 ActivVisionTools 1 2 Edition 2 April 2001 ActivVisionTools 1 3 Edition 3 September 2001 ActivVisionTools 2 0 Edition 4 November 2002 ActivVisionTools 2 1 Edition 5 January 2005 ActivVisionTools 3 0 Edition 6 February 2006 ActivVisionTools 3 1 Edition 7 May 2008 ActivVisionTools 3 2 All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording or otherwise without prior written permission of the publisher More information about ActivVisionTools can be found at http www activ vision tools com How to Read This Manual This manual explains how to use ActivGeoCalib to convert the results of other Activ VisionTools from image to world 3D coordinates It describes the functionality of ActivGeoCalib and its cooperation with other ActivVisionTools with Visual Basic examples Before reading this man ual we recommend to read th
11. ault CamType N Size v Size e __ Dete Delete All Gray 8 Color Progrdgsive Field pes ia Pixel Size pn Distance cm Pan Deg Rotation Deg Execute Stop I Cohnected Mots Paramdters Slant Deg Unit Pixel 7 Single Run I Trigger Save A eres 2 Calibrate Save Load Grabbing select your frame grabber 4 specify additional parameters if necessary nam a r 6 switch to Run mode and configure your vision system Figure 2 1 Specifying parameters of the vision system ActivVisionTools 3 2 Your Fast Track to Solutions 12 Using ActivGeoCalib Visual Basic Example 2 2 Grabbing Images of the Calibration Plate The main part of the calibration process consists of acquiring images of the calibration plate in different positions and orientations relative to the vision system Please note that the more you vary the position and orientation the better the calibration results Therefore place the plate so that it appears in different corners at different distances to the camera and in different planes i e tilt it for some images Preparation for the following example If you worked on the previous example you may continue using this project Otherwise open the project grabbing geocalib_grabbing vbp and execute it Run gt Start or via the corresponding button If you want to experiment with the calibration image sequence calib cali
12. b_3cm_1 seq select it in the combo box Input File The following steps are visualized in figure 2 2 We recommend to switch to continuous grabbing by clicking Run before positioning the calibration plate Thus you can assure that the plate is fully visible Then press Stop You acquire calibration images by clicking Grab in AVTGeoCalibration ActivGeo Calib now tries to find the plate in the image by extracting the surrounding black square frame and the 49 circular markings If the image could be processed successfully the extracted frame and markings are overlayed on the image Otherwise AVTViewStatus displays a corresponding error message To acquire images from the calibration image sequence also click Grab the image sequence consists of twelve images You can browse the list of already acquired images with the slider labelled Image List or by typing an image number in the neighboring text field Moreover you can delete an image from the list by clicking Delete This may be useful if you acquired multiple images of the same setting by mistake You can save a calibration image by clicking Save Image in AVITViewFG and specify ing a file name in the appearing file selection box As described in section 1 1 on page 2 and in the following section one of the images serves as the so called reference image i e it is used to describe
13. e 2 3 0 73 was specified this corresponds to the plane of the markings on the calliper rule If your plane of measurement is closer to the camera than the calibration plate you must specify the distance as a negative value Now click Calibrate to start the calibration process which will need some time de pending on the number of calibration images As a result the computed position and orientation of the reference frame relative to the vision system see section 1 1 on page 2 will be displayed in the text fields of the frame Calibration Besides these param eters the calibration process also determines the exact values of the internal parameters of the vision system and displays them in the text fields of the frame Camera Lens Furthermore it calculates the 3D size area of the pixel in the center of the image The calibration data is automatically saved in the project s description file DSC file see the manual Getting Started with ActivVisionToolssection 1 2 4 on page 9 for more information thus whenever you start the project again the calibration data is automat ically loaded If you want to use the calibration data for other projects as well save it to a separate file by clicking Save in AVTGeoCalibration and specifying a file name in ActivGeoCalib 2008 04 23 2 3 Calibrating 15 specify the offset between the calibration plate and the plane of measuring select the reference image
14. e and specifies its length in the desired unit from this the size of a pixel in this unit is calculated and then used to convert results from pixels to the new unit In comparison to AVTViewCalibration ActivGeoCalib offers the following advantages First it calibrates both the height and the width of a pixel while AVITViewCalibration assumes square pixels Secondly ActivGeoCalib takes into account that the size of a pixel varies over the image plane due to projection in general and to lens distortions And thirdly ActivGeoCalib allows to measure in arbitrarily oriented planes while the results of AVTViewCalibration are valid only in planes which are parallel to the camera chip Summarizing you can use AVTViewCalibration to get a quick but rough estimate of results in world coordinates for high accuracy measurements you should use ActivGeoCalib 1 2 The Sub Tools of ActivGeoCalib eo ActivGeoCalib provides only a master tool AVTGeoCalibration In figure 1 4 it is shown T in an example ActivVisionTools application where it is used to transform the results of Activ Measure into 3D ActivGeoCalib 2008 04 23 1 2 The Sub Tools of ActivGeoCalib 7 ActivView HA AVTGeoCalibration la x The Sub Tools of ActivGeoCalib Calibration Plate caltab_30mm descr j mm File Camera Lens 0 63 Cell Size X 7 36 vium J Cell Size Y 7 40 v um Focal Length 13 17 mm J Telecentric Calibration I
15. e manual Getting Started with Activ VisionTools which introduces the basic concepts of ActivVisionTools and the User s Manual for Activ View to learn how to load and display images To follow the examples actively first install and configure ActivVisionTools as described in the manual Getting Started with Activ VisionTools For each example in this manual there is a corresponding Visual Basic project these projects can be found in the subdirectory exam ples manuals activgeocalib of the ActivVisionTools base directory you specified during installation default C Program Files MVTec ActivVisionTools Of course you can also create your own Visual Basic projects from scratch We recommend to create a private copy of the example projects because by experimenting with the projects you also change their state which is then automatically stored in the so called description files extension dsc by ActivVisionTools Of course you can restore the state of a project by retrieving the corresponding description file from the CD _ Contents About ActivGeoCalib 1 1 1 Unweducme AchvGesCalib gt Sh ca eee Ee eR ERR ES SO 2 1 2 The Sub Tools of ActivGeoCalib a oaoa 6 Using ActivGeoCalib 9 2A Getting Started o s a recroiser w kai k Bo eee e E oe E 10 2 2 Grabbing Images of the Calibration Plate o oo 12 2a Caibrang oc ORG Ree eA Phe ew a eE Seabee owes 14 Combining ActivGeoCalib with other ActivVisionTools 17 3 1 C
16. e smaller ceramics calibration plates are installed automatically Results ActivGeoCalib calculates two types of parameters of your vision system internal parameters e g the precise focal length the size of a cell on the camera chip or the distortion caused by an imperfect lens and external parameters i e the position and the orientation of the vision system relative to a so called reference frame see below The meaning of the four external parameters is visualized in figure 1 2 In the ideal position depicted in the middle the camera is pointed directly at the calibration plate Figures 1 2a amp b show the meaning of the angular parameter slant figures 1 2c amp d show the meaning of the angular parameter pan figures 1 2e amp f show the angular meaning of the parameter rotation and figures 1 2g amp h show the meaning of the parameter distance ActivGeoCalib automatically passes the calculated parameters on to other Activ VisionTools which use them to convert their results from image to world coordinates Another possible use of the parameters is during the setup of the vision system If you want to assure a certain position ActivVisionTools 3 2 Your Fast Track to Solutions 4 About ActivGeoCalib O decrease distance e rotate left a slant up original position Figure 1 2 The position and orientation of the vision system a amp b slanting up and dow
17. elative to the camera Using ActivGeoCalib you can calibrate vision systems based on standard lenses as well as on the so called telecentric lenses The Fundamental Problem of Imaging During the process of imaging i e the projection of the 3D world by a vision system onto the image plane camera chip the 3D information is lost This means that you cannot reconstruct the 3D shape of an object from a single image of it at least not without further information about the vision system or about the object e g its position relative to the camera By calibrating a vision system you extract information about it e g its focal length or its po sition and orientation relative to the world However even with such information you cannot fully reconstruct the 3D world from a single image For example you can determine the 3D size of an object only if you know its distance from the vision system when using a standard lens How to Calibrate a Vision System Most calibration methods extract information about the vision system by grabbing one or more images of a special calibration object whose shape is known precisely In other words they examine how a known object is imaged by the vision system and from this draw conclusions about the vision system itself ActivGeoCalib is also based on this approach It uses a planar calibration object marked with 49 circles see figure 1 1 which is available in different sizes e g 10mm
18. found on the lens itself If you are using a telecentric lens check the corresponding box Figure 2 1 shows the correct settings for the calibration image sequence Now select your image acquisition device in the combo box Name of AVTViewFG If you want to experiment with the calibration image sequence select File Depending on the image acquisition device you may need to specify additional param eters Please consult the User s Manual for ActivView section 2 1 on page 16 for more information If you want to work with subsampled images i e images where only every second pixel in both image dimensions is used select Half Size in the the combo box Size By clicking Run you connect to the image acquisition device and switch it to the con tinuous grabbing mode at the same time In this mode you can configure your vision system e g adapt the focus or the aperture ActivGeoCalib 2008 04 23 2 1 Getting Started 11 select the calibration plate 2 specify camera parameters from datasheet a Specifying Known Parameters Kalibration Plate caltab_30mm deser hd 0 63 mm File Q Camera Kens 5 Cell Size x o e1 Acquisition Interface Cell Size Y om o gt 1394IIDC Name Detect Refresh helr ma mee Z A r Device r Calibration Images lt 0004470100044027 1 Board Port Image List 4 Reference Image 4 Format Name J def
19. ivDataView by clicking on AVTMeasure with the right mouse button and selecting Data View Enable the display by checking v Enable Update You can select a unit in the combo box Unit of AVTGeoCalibration The measuring results displayed in ActivDataView are immediately converted into the selected unit As you can see the measured 3D distance between the markings column Distance Center is very accurate even though the camera is pointed at the plane of measurement in an oblique angle more than 40 slant ActivGeoCalib 2008 04 23 3 1 Converting Results of other ActivVisionTools 19 O open AVTDataView via a click on AVTMeasure with the right mouse button w Converting the Results of ActivMeasure to Other Units lo x r Calibration Plate Name caltab_30mm descr kd Thickness 073 mm File r Camera Lens Cell Size Xx 7 36 yi um A Cell Size Y 7 40 vium Focal Length IE Fa mm Telecentric r Calibration Images Image List 4 gt Reference Image 4 gt Grab Delete Delete All r Calibration Pixel Size 9246 519 ur Distance J 14 69 cm Pan 0 62 Deg Rotation 3 14 Deg Slant 43 39 Deg Unit mm X Calibrate Save Load flight gt Dark 7 Edge Type Edge Pairs x Edge Grouping fal Edges z Edge Selection 2 5 oO O oO 2 lt PI gt se suet ox A 5B
20. ject comparison geocalib_comparison vbp Execute the application Run gt Start or via the corresponding button Open AVT ViewFG by clicking into AVIView with the right mouse button and selecting Im age Acquisition in the popup menu Select the image calib rule_01 in the combo box Input File The following steps are visualized in figure 3 2 D To perform the 2D calibration using AVTViewCalibration select AVTViewCalibra tion1 in the combo box ActivVisionTool of AVTViewROI Then click and draw a line over the markings in the image You can position the line precisely by dragging the pick points Place it as shown in the figure this distance corresponds to 10 0 mm Q Select the desired unit mm in the combo box Unit of AVTViewCalibration Then specify the length of the line 10 in the text box Length Line and press Enter Automatically all measured distances and positions are converted into the selected unit Now take a look at the column Distance Center in ActivDataView The distances increase from marking to marking whereas in reality the markings are spaced evenly The reason for this error is that the basic assumption behind AVITViewCalibration is violated in this example The camera chip is not parallel to the plane of measurement more than 40 slant In consequence the closer markings are to the camera the bigger their distance is in the image and this directly
21. l cen zhe Selected Tool Yaw z Eror Wro z Inactive Tools cay gt Selected Yew z Special Margin I Magenta 7 Display Mode Line Width Fes 1 344 5 ms Pick Point Line Width r Display Image z J Text Background Contrasting Contours 2 5 oO O oO 2 lt color of the selected ROI of the other ROls of the selected tool or of the ROIs of other tools color of the crosses or of the square frame GB color of the selected pick point drawing mode for the frame D look up table for image display display contours with contrasting border line width of the ROIs or of the lines Figure 4 1 Adapting the display of ROIs and results ActivVisionTools 3 2 Your Fast Track to Solutions 26 Tips amp Tricks 4 2 Rectifying Images for Other ActivVisionTools The calibration information cannot only be used to convert features computed by other Activ VisionTools but also to transform the image such that it looks as if the camera was looking exactly from above onto the scene This transformation is called image rectification There are two typical reasons for rectifying images For tools like ActivOCR the objects to process must not appear perspectively distorted in order to be recognized Many features describing blobs cannot be calculated exactly in 3D from the perspectively distorted image
22. mages Image List 4 gt Reference Image 4 gt Grab Delete Delete All Calibration Pixel Size 8245 519 um Distance 1469 cm Pan 062 Deg Rotation 314 Deg Slant 4339 Deg Unit mm X Calibrate Save Load Name Thickness 2 T oO O oO lt Light gt Dark Edge Type Seek ActivVisionTool AvVTMeasure1 ha ROI v o Jedge Pairs v Edge Grouping faa Edges v Edge Selection 4 F Object Id Width Distance Center Row Center Column Center A gt 17 Ege Strength 0 0 330 4 987 10 858 0 001 ff gt Noise Level 1 0 323 4 987 5871 0 076 2 0 350 5 003 0 884 0 149 sf Fie Rown 3 0360 4977 4418 0 222 4 0 380 8 094 0 293 Stanaara v Accuracy IV Enable Update ActivMeasure ActivDataView Figure 1 4 ActivGeoCalib together with suitable other tools in a measuring application ActivVisionTools 3 2 Your Fast Track to Solutions 8 About ActivGeoCalib ActivGeoCalib 2008 04 23 Chapter 2 Using ActivGeoCalib This chapter will explain how to calibrate your vision system using ActivGeoCalib How the extracted information is used by other ActivVisionTools is the topic of the next chapter The corresponding Visual Basic projects can be used with live images from your own vision system or with a provided sequence of calibration images 21 Getting Stard s oces ke ee ee ea e
23. n c amp d panning left and right e amp f rotating left and right g amp h decreasing and increasing the distance and orientation of the camera the parameters tell you how to move the camera accordingly For example if the camera is to be pointed directly at a certain position all angular parameters should be zero if a parameter is not zero rotate the camera correspondingly by the calculated value Of course you must calibrate the system again after adjusting the camera ActivGeoCalib 2008 04 23 1 1 Introducing ActivGeoCalib 5 imaged part of the plane of measurement 2D image coordinates i oe columns e gt rows y center of the image peme T i Eo V rows 7 origin of the reference we frame in the center of the a calibration plate Pe 2 G 8 e 0 lt Figure 1 3 The reference frame The Reference Frame As mentioned above one fundamental problem remains even after calibration The size of an object can only be reconstructed if its distance to the vision system is known or more precisely if it is lying in a known plane relative to the vision system Therefore you must specify this plane the so called reference frame before you can start to measure anything in it You specify the reference frame with the help of the calibration plate Place the plate in such a way that it is parallel to the plane you want to measure in afterwards for example if you
24. oCalib ActivVisionTools 3 2 Your Fast Track to Solutions 22 Combining ActivGeoCalib with other ActivVisionTools ActivGeoCalib 2008 04 23 Chapter 4 Tips amp Tricks 2 8 e o 0 im lt This chapter contains additional information that facilitates working with ActivGeoCalib e g how to modify the graphical display of results and how to rectify images 4 1 Adapting the Display of Results 4 2 Rectifying Images for Other ActivVisionTools 23 24 Tips amp Tricks 4 1 Adapting the Display of Results Using al You can adapt the way results and ROIs are displayed using AVTViewDisplayModes which is a support tool of Activ View Visual Basic Preparation for the following example Example If you worked on the example in the previous chapter you may continue using this project Otherwise open the project display geocalib_display vbp Execute the application and load the calibration image sequence calib calib_3cm_1 seq Acquire an image from the sequence for calibration by clicking Grab in AVT GeoCalibration The following steps are visualized in figure 4 1 Experiment by choosing different settings for the display parameters and watching the result The first steps can only be tested if there exist some regions of interest ROIs e g for AVITViewCalibration or ActivMeasure QQOQOLOD Open AVTViewDispla
25. onverting Results of other ActivVisionTools 0 18 3 2 ActivGeoCalib vs AVITViewCalibration 20 Tips amp Tricks 23 4 1 Adapting the Display of Results 2 22000 24 4 2 Rectifying Images for Other ActivVisionTools 26 Chapter 1 About ActivGeoCalib This chapter will introduce you to the features and the basic concepts of the calibration tool ActivGeoCalib How to use ActivGeoCalib is described in more detail in chapter 2 on page 9 and chapter 3 on page 17 1 1 Introducing ActivGeoCalib 2 2 2 2 e ee eee ee eee 1 2 The Sub Tools of ActivGeoCalib 2 8 e o 0 im lt 2 About ActivGeoCalib 1 1 Introducing ActivGeoCalib With the help of ActivGeoCalib the results of other Activ VisionTools e g distances measured by ActivMeasure or shape features calculated by ActivFeatureCalc are automatically converted from image coordinates pixels to 3D world coordinates e g millimeters with high accuracy All ActivGeoCalib needs for this is to grab a set of images of a special calibration object placed in front of your vision system Please note that ActivGeoCalib cannot reconstruct the full 3D information as parts of it are irrevocably lost when an object is imaged i e projected by the camera on the camera chip As a consequence all inspected objects must lie in one plane which can have an arbitrary distance and orientation r
26. the plane other ActivVisionTools measure in Therefore position the calibration plate parallel to the desired plane of measurement in at ActivGeoCalib 2008 04 23 2 2 Grabbing Images of the Calibration Plate 13 acquire calibration images by clicking Grab G browse images using the slider if the image could be processed successfully delete images by clicking Delete the markings of the plate are visualized otherwise an error message appears I x Grabbing Calibration Images r Calibration Plate r Camera Lehs Cell Size x Acquisition Interface 1394IDC v Name Cell Size Y Reteh Focal Length Detect Device alibration Images 0004470100044027 v Board R ference Image L r Format r Frame default v CamType Full Size gt Sis N Delete Delete All Gray 8 v Color Progressive v Field Eeter Pixel Size p Distance cm p Grabbing Pan Deg Rotation Deg Execute Stop IV Connected Single Run J Trigger More Parameters a Slant Deg Unit Pixel hd Save Window Calibrate Save Load Save Image O in continuous grabbing mode position 4 optional save the calibration images the calibration plate then click Stop Figure 2 2 Grabbing images of the calibration plate least one image and note its number ActivVisionTools 3 2 Your Fast
27. tivGeoCalib vs AVTViewCalibration 00 cece eevee 20 17 2 8 e o 0 im lt 18 Combining ActivGeoCalib with other ActivVisionTools 3 1 Converting Results of other ActivVisionTools If calibration data is present in an ActivVisionTools application results are automatically con verted into the selected unit In the example application the task is to measure the distance of markings on a calliper rule using ActivMeasure isual Basi i V a Preparation for the following example Example If you worked on the example in the previous chapter and used the shown settings you may continue using this project At design time add AVTMeasure and AVT MeasureResults to the form by double clicking Jf and with the left mouse button Otherwise open the project units geocalib_units vbp Execute the application Run gt Start or via the corresponding button and open AVTViewFG by clicking into AVTView with the right mouse button and selecting Im age Acquisition in the popup menu Select the image calib rule_01 in the combo box Input File To measure the markings on the calliper rule create a line shaped ROI for AVT Measure AVTViewROI can be opened via the context menu of AVTView If neces sary select the parameters for ActivMeasure as shown in figure 3 1 The following steps are visualized in figure 3 1 D To display the measurement results open Act
28. yModes by clicking on AVTView with the right mouse button and selecting Display Modes in the popup menu Change the color of the currently selected ROI Select another ROI by clicking into its vicinity Change the color of the other not selected ROIs of the currently selected tool Change the color of the ROIs of the other not selected tools Select another tool in the combo box ActivVisionTool of AVTViewROI if this box contains more than one item Change the color of the selected pick point Select another pick point by clicking into its vicinity Change the LUT look up table that is used to display the image Change the line width of the ROIs or of the crosses and of the square frame Change the color of the crosses Group I or of the square frame Group IT Change the way the frame is displayed filled or margin only If you check this box the crosses are displayed with a contrasting border which makes them more visible if you chose a dark color for them ActivGeoCalib 2008 04 23 4 1 Adapting the Display of Results 25 open AVTViewDisplayModes via a click on AVTView with the right mouse button w Adapting the Display Calibration Plate Name caltab_30mm descr hi Thickness 073 mm Fie Camera Lens Pall Giza 736 owl um mtjActivYiewDisplayModes x r Display Region of Interest r Display Results Active ROI Micreen gt Group Yeow zf Error ROI Mire z Group I
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