Changes between Version 24 and Version 25 of Tutorial/GeometricCalibration


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Timestamp:
Jan 23, 2015, 1:51:39 PM (6 years ago)
Author:
vaillant1p
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  • Tutorial/GeometricCalibration

    v24 v25  
    55Open again a test image in 'UVMAT_DEMO01_pair' (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/).
    66
    7 We shall use the diameter of the half cylinder visible on the upper let of the image to set the calibration. Its physical diameter  is 2cm. The corresponding diameter in pixels can be obtained with the ruler displayed by the menu bar '''Tools/ruler''' of uvmat.
     7We shall use the diameter of the half cylinder visible on the upper let of the image to set the calibration. Its physical diameter  is 2cm. The corresponding diameter in pixels can be obtained with the ruler displayed by the menu bar '''[Tools/ruler]''' of uvmat.
    88
    9 First zoom on the cylinder to optimize the precison. Select '''zoom on''', press the left mouse button and adjust the field with the directional key board arrows. Then unselect '''zoom on''' to allow for other mouse actions (otherwise zoom has priority). It is also useful to increase the contrast at the cylinder edge by setting '''MaxA''' to 100 in the frame '''Scalar''' (right side of uvmat).
     9First zoom on the cylinder to optimize the precison. Select '''[zoom on]''', press the left mouse button and adjust the field with the directional key board arrows. Then unselect '''[zoom on]''' to allow for other mouse actions (otherwise zoom has priority). It is also useful to increase the contrast at the cylinder edge by setting '''MaxA''' to 100 in the frame '''[Scalar]''' (right side of uvmat).
    1010
    11 Then select the menu bar '''Tools/ruler''', press the left hand mouse button on the cylinder edge, draw a diameter keeping the mouse pressed, release it on the opposite edge. The length in pixels, 140, is displayed, so the scaling factor is 140/2=70 pixels/cm.
     11Then select the menu bar '''[Tools/ruler]''', press the left hand mouse button on the cylinder edge, draw a diameter keeping the mouse pressed, release it on the opposite edge. The length in pixels, 140, is displayed, so the scaling factor is 140/2=70 pixels/cm.
    1212
    13 Open the menu bar '''Tools/geometric calibration'''. A new GUI '''geometry_calib''' appears on the right side. Activate the upper menu bar '''!Tools/Set scale''' on this GUI and introduce the value 70 in the edit box which pops up, and validate with '''OK'''. A set of calibration point coordinates appears in the table '''[!ListCoord]''' of the GUI.
     13Open the menu bar '''[Tools/geometric calibration]'''. A new GUI '''geometry_calib''' appears on the right side. Activate the upper menu bar '''[!Tools/Set scale]''' on this GUI and introduce the value 70 in the edit box which pops up, and validate with '''[OK]'''. A set of calibration point coordinates appears in the table '''[!ListCoord]''' of the GUI.
    1414
    15 To see the calibration points on the image, first display the whole image by unselecting '''fix''' (tag '''[!CheckFixLimits]''') in the frame '''Axes''' of uvmat. Then press '''PLOT PTS''' in '''geometry_calib'''.
     15To see the calibration points on the image, first display the whole image by unselecting '''[fix]''' (tag '''[!CheckFixLimits]''') in the frame '''[Axes]''' of '''uvmat'''. Then press '''[PLOT PTS]''' in '''geometry_calib'''.
    1616
    17 To perform the calibration, press '''APPLY''', first with the default option 'rescale' in '''calib_type''', and confirm by pressing '''[OK]''' in the dialog box. The image is now displayed in phys coordinates. A xml file 'images.xml', containing the calibration parameters and reference point coordinates, has been created in the folder 'UVMAT_DEMO01_pair' (it should be identical with the file 'images.ref.xml' put for reference). Note that the xml file name reproduces the name of the folder containing the images, so that images from different cameras should not be put in the same folder.
     17To perform the calibration, press '''[APPLY]''', first with the default option 'rescale' in '''calib_type''', and confirm by pressing '''[OK]''' in the dialog box. The image is now displayed in phys coordinates. A xml file 'images.xml', containing the calibration parameters and reference point coordinates, has been created in the folder 'UVMAT_DEMO01_pair' (it should be identical with the file 'images.ref.xml' put for reference). Note that the xml file name reproduces the name of the folder containing the images, so that images from different cameras should not be put in the same folder.
    1818
    1919[[Image(Calib.JPG)]]
     
    2222The origin of the phys coordinates is now arbitrary. It is more convenient to have it for instance at the centre of the cylinder, now at (x,y)=(1.69, 4.05).
    2323
    24 To get the precise position of the cylindre, it is useful to introduce a projection circle, using in '''uvmat''' the menu bar command Projection '''Projection object/ellipse'''. In '''set_object''', select '''!ProjMode=''''none', so that the line is just used as a marker, without projection operation. Set XMax=1, YMax=1, the radius of the circle, and the coordinates (1.69, 4.05) of the centre in the table '''Coord'''. Then press '''REFRESH'''. To optimise the visualisation, zoom in and increase the image contrast to MaxA=100.
     24To get the precise position of the cylindre, it is useful to introduce a projection circle, using in '''uvmat''' the menu bar command Projection '''[Projection object/ellipse]'''. In '''set_object''', select '''[!ProjMode]'''='none', so that the line is just used as a marker, without projection operation. Set XMax=1, YMax=1, the radius of the circle, and the coordinates (1.69, 4.05) of the centre in the table '''Coord'''. Then press '''[REFRESH]'''. To optimise the visualisation, zoom in and increase the image contrast to MaxA=100.
    2525
    26 To shift the coordinates, activate in '''geometry_calib''' the menu bar command '''!Tools/Translate points''', and fills  (x=-1.69, y=-4.05) in the edit box which pops up. The phys coordinates of the calibration points are then shifted, and a new calibration put the cylindre centre at the origin (0,0).
     26To shift the coordinates, activate in '''geometry_calib''' the menu bar command '''[!Tools/Translate points]''', and fills  (x=-1.69, y=-4.05) in the edit box which pops up. The phys coordinates of the calibration points are then shifted, and a new calibration put the cylindre centre at the origin (0,0).
    2727
    2828put in the same folder.
     
    3131To repeat the calibration for several image series obtained with the same camera at the same position, different methods can be used.
    3232
    33 -Copy the xml to the appropriate location, with the same name (but extension .xml) and path as the flle containing the image series. This is however not appropriate in general as the xml file contains other information, in particular about image timing. 
     33- Copy the xml to the appropriate location, with the same name (but extension .xml) and path as the flle containing the image series. This is however not appropriate in general as the xml file contains other information, in particular about image timing. 
    3434
    35 -Open with '''uvmat''' one of the image of the series to calibrate, select '''Tools/geometric calibration''', and in the GUI '''geometry_calib''', the menu bar '''!Import/All''', then press''' APPLY'''. For further repetitions, the GUI '''geometry_calib''' can be left opened while new image series are opened, and '''APPLY''' repeated each time without importing the calibration data again. [[BR]]
     35- Open with '''uvmat''' one of the image of the series to calibrate, select '''[Tools/geometric calibration]''', and in the GUI '''geometry_calib''', the menu bar '''[!Import/All]''', then press''' [APPLY]'''. For further repetitions, the GUI '''geometry_calib''' can be left opened while new image series are opened, and '''[APPLY]''' repeated each time without importing the calibration data again. [[BR]]
    3636
    37 -In case of many image series, use '''REPLICATE''' instead of '''APPLY''' in the GUI '''geometry_calib. '''Then select the 'campaign' to calibrate, i.e. the folder containing the series of experiments. Then in the new GUI '''browse_data''', select the set of experiments and the corresponding set of data series to which the calibration must apply (this is used like '''Open campaign''' in '''uvmat''').
     37- In case of many image series, use '''[REPLICATE]''' instead of '''[APPLY]''' in the GUI '''geometry_calib'''. Then select the 'campaign' to calibrate, i.e. the folder containing the series of experiments. Then in the new GUI '''browse_data''', select the set of experiments and the corresponding set of data series to which the calibration must apply (this is used like '''[Open campaign]''' in '''uvmat''').
    3838
    3939
    4040== Calibration with reference points ==
    41 The more general method of calibration consists in using a set of reference points whose physical coordinates are known. Open with '''uvmat''' an image in 'UVMAT_DEMO06_PIVconvection/Dalsa1' (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/)
     41The more general method of calibration consists in using a set of reference points whose physical coordinates are known. Open with '''uvmat''' an image in 'UVMAT_DEMO06_PIVconvection/Dalsa1' (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/).
    4242
    43 Select in the menu bar '''Tools/geometric calibration'''. Mark the four box corners of the box with the mouse (left hand button). Their coordinates in pixels are displayed in the two last column of the table '''!ListCoord''' in the GUI '''geometry_calib'''. To clear the table for corrections push the button '''CLEAR_PTS''', or for a single line, use the key board 'Delete' button. To improve the position on the image, use the zoom and directional arrows. We find the coordinates of the four calibration points in pixels:
     43Select in the menu bar '''[Tools/geometric calibration]'''. Mark the four box corners of the box with the mouse (left hand button). Their coordinates in pixels are displayed in the two last column of the table '''[!ListCoord]''' in the GUI '''geometry_calib'''. To clear the table for corrections push the button '''[CLEAR_PTS]''', or for a single line, use the key board 'Delete' button. To improve the position on the image, use the zoom and directional arrows. We find the coordinates of the four calibration points in pixels:
    4444
    4545(X,Y)=(80.3, 81.6), (982.3, 86.1), (978.9, 937.4), (71.2, 929.5).
    4646
    47 The corresponding physical coordinates are known to be
     47The corresponding physical coordinates are known to be:
    4848
    4949(x,y)=(0,0),(58.8,0),(58.8,55.1),(0,55.1), with an origin (0,0) taken at the lower left (and z=0).
     
    5151Introduce those in the two first columns of the table '''[!ListCoord]'''. This can be conveniently done by copy-paste Matlab vector x=[0 58.8 58.8 0] in the upper line of the x column, and y=[0 0 55.1 55.1] in the y column (use carriage return to validate the input).
    5252
    53 To perform the calibration, press '''APPLY''', first with the default option 'rescale' in '''calib_type'''. The image is now displayed in phys coordinates. We observe that the rectangular frame is slightly rotated. Furthermore the displayed precision, about 3 pixels, is not excellent.
     53To perform the calibration, press '''[APPLY]''', first with the default option 'rescale' in '''calib_type'''. The image is now displayed in phys coordinates. We observe that the rectangular frame is slightly rotated. Furthermore the displayed precision, about 3 pixels, is not excellent.
    5454
    5555To improve the precision we then apply the option 'linear' in '''calib_type''', which seeks a general linear transform, including rotation. The precision is indeed improved to about 1 pixel. The previous xml file has been saved with a ~, ('Dalsa1.xml~') so it can be reverted in case of error.
    5656
    5757== Calibration with a target grid ==
    58 Most precise and general calibration relies on the use of a target grid. As an example, open in uvmat the image ima_6 in 'UVMAT_DEMO07_GeometryCalibration/Dalsa1' (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/). Open the menu bar '''Tools/geometric calibration '''and''' '''pick four corner points ABCD with the mouse define the periphery of the phys grid selected for calibration. The first point A will define the phys axis origin while AB defines the x axis and AD the y axis. AB and DC should be parallel on the phys grid (see fig). Then select''' !Tools/Detect grid '''on the upper menu bar of''' geometry_calib: '''you get a new GUI '''detect_grid''' in which you define (in phys units) the grid mesh and the positions of the  first and last points on each axis. A z position can be defiend as well, do not fill it in this example. The option white markers is selected (by default) indicating that the grid is white (the opposite option would be needed for a grid made of black crosses on a white background). After validation by '''OK''', the detected grid appears on uvmat (see fig).
     58Most precise and general calibration relies on the use of a target grid. As an example, open in uvmat the image ima_6 in 'UVMAT_DEMO07_GeometryCalibration/Dalsa1' (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/). Open the menu bar '''[Tools/geometric calibration] '''and pick four corner points ABCD with the mouse define the periphery of the phys grid selected for calibration. The first point A will define the phys axis origin while AB defines the x axis and AD the y axis. AB and DC should be parallel on the phys grid (see fig). Then select''' [!Tools/Detect grid] '''on the upper menu bar of''' geometry_calib''': you get a new GUI '''detect_grid''' in which you define (in phys units) the grid mesh and the positions of the  first and last points on each axis. A z position can be defiend as well, do not fill it in this example. The option white markers is selected (by default) indicating that the grid is white (the opposite option would be needed for a grid made of black crosses on a white background). After validation by '''[OK]''', the detected grid appears on uvmat (see fig).
    5959
    6060If a  point is not correct, select the option '''[!CheckEnableMouse]''' in '''geometry_calib'''. Then you can adjust the point marker by selecting it with the (left button) mouse and moving it while keeping the mouse pressed (when adjustement is finished, nselected the option  '''[!CheckEnableMouse]''' to avoid spurious point creation with the mouse).
    6161
    62 If the grid image is of poor quality, it is alternatively possble to mark all the points by the mouse, using the '''!Tools/Create''' grid instead of '''!Tools/Detect grid''' in geometry_calib (not convenient in general).
     62If the grid image is of poor quality, it is alternatively possble to mark all the points by the mouse, using the '''[!Tools/Create]''' grid instead of '''[!Tools/Detect grid]''' in geometry_calib (not convenient in general).
    6363
    64 Once the grid has been marked, the calibration can be performed by the press button '''APPLY'''. We observe that the simple option 'rescale' is not appropriate in this case: a perspective effect is clearly visible, together with a non-linear deformation (grid lines are curved on the image). Therefore select the option '3D_quadr' which applies a 3D projection and quadratic correction. The grid image now appears of good quality in phys coordinates.
     64Once the grid has been marked, the calibration can be performed by the press button '''[APPLY]'''. We observe that the simple option 'rescale' is not appropriate in this case: a perspective effect is clearly visible, together with a non-linear deformation (grid lines are curved on the image). Therefore select the option '3D_quadr' which applies a 3D projection and quadratic correction. The grid image now appears of good quality in phys coordinates.
    6565
    6666== '''Merging the images of several cameras:''' ==