Changes between Version 42 and Version 43 of Tutorial/GeometricCalibration


Ignore:
Timestamp:
Jan 26, 2015, 11:51:18 AM (6 years ago)
Author:
vaillant1p
Comment:

--

Legend:

Unmodified
Added
Removed
Modified
  • Tutorial/GeometricCalibration

    v42 v43  
    6363If 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).
    6464
    65 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. 
     65Once 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.
    6666
    67 This 3D calibration relies on the [https://servforge.legi.grenoble-inp.fr/projects/soft-uvmat/search?q=attachment%3A3D_view.pdf pinhole camera model] (see [https://servforge.legi.grenoble-inp.fr/projects/soft-uvmat/search?q=wiki%3AUvmatHelp%23GeometryCalib UvmatHelp#GeometryCalib] section 8.1). It involves ''intrinsic parameters'' which characterize the optical system (camera and objective lens) and ''extrinsic parameters'' which describe the translation and rotation of the camera with respect to the physical coordinates. detailler sur le GUI. The intrinsic parameters are shown in the frame '''[Intrinsic Parameters] '''in the GUI '''geometry_calib'''. These are the focal lenghts (in pixel size on the sensor) '''[fx]''' and '''[fy]''',  the quadratic radial distortion coefficient '''[kc]''' and the coordinates '''[Cx]''' and '''[Cy]''' of the optical centre for this distortion (expressed in pixels on the image).
     67This 3D calibration relies on the [https://servforge.legi.grenoble-inp.fr/projects/soft-uvmat/search?q=attachment%3A3D_view.pdf pinhole camera model] (see [https://servforge.legi.grenoble-inp.fr/projects/soft-uvmat/search?q=wiki%3AUvmatHelp%23GeometryCalib UvmatHelp#GeometryCalib] section 8.1). It involves ''intrinsic parameters'' which characterize the optical system (camera and objective lens) and ''extrinsic parameters'' which describe the translation and rotation of the camera with respect to the physical coordinates. detailler sur le GUI. The intrinsic parameters are shown in the frame '''[Intrinsic Parameters] '''in the GUI '''geometry_calib'''. These are the focal lenghts (in pixel size on the sensor) '''[fx]''' and '''[fy]''',  the quadratic radial distortion coefficient '''[kc]''' and the coordinates '''[Cx]''' and '''[Cy]''' of the optical centre for this distortion (expressed in pixels on the image). The extrinsic parameters are shown in the frame  '''[Extrinsic Parameters]. '''It indicates in particular the translation T_z which represents the distance from the camera to the origin of the phys coordinates. Note that the calibration grid has been assumed by default to be at z=0, but this can be changed by selecting '''[!Tools/Translate points]''' in '''geometry_calib''' and entering a translation in ''z'' for the grid point coordinates.
     68
     69A last''' '''item needed to define calibration in a 3D context is the determination of the plane of the object in the phys coordinates. It is assumed by default to be the plane z=0, but this can be changed by the menu bar option '''[!Tools/Set slice] '''of uvmat. It is then possible to change the assumed z position, keeping the same calibration. Observe the corresponding change in the grid scale, since the same grid is then assumed to be at a different distance.
    6870
    6971== 3D calibration improved by multiple planes: ==
     
    7274Open su the grid image is correctly set, click on the '''[APPEND LIST]''' button in '''[Point Lists]'''. This will save the grid as 'img~.xml'. This document is saved in the same folder as the image. To open this document select '''[Import.../Calibration points]'''.
    7375
    74 Durind the calibration, some intrinsic parameters are determined 
     76Durind the calibration, some intrinsic parameters are determined
    7577
    7678Now that the calibration is made for the first image we need to do it for the other ones (you can also open the different grids 'img.ref~.xml' to skip the calibration). Once a document is open, the grid is shown in '''uvmat''', to save it in the '''[Point Lists]''' click on '''[APPEND LIST]''', it will appear below the first saved document.
     
    8284'''Note:''' if the serie is missing some images (ie the increment from one image to another is not steady), '''uvmat''' will not allow you to use the arrow '''[->]'''  to move from an image to another if the increment is set. To avoid this  delete the number in [increment], you will then be able to go from an  image to another.
    8385
    84 '''Note:''' These corrections take the hypothesis of ''z=0''. If you want to change and set the correct height of the grid, select '''[!Tools/Translate points]''' in '''geometry_calib''' and enter the correct value of ''z''.
    85 
    8686== '''Merging the images of several cameras:''' ==
    8787z position}}