# Changes between Version 40 and Version 41 of Tutorial/GeometricCalibration

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Timestamp:
Jan 26, 2015, 10:54:56 AM (6 years ago)
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• ## Tutorial/GeometricCalibration

 v40 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. Durind the calibration, some intrinsic parameters are determined and shown in [Intrinsic Parameters] in '''geometry_calib'''. These are the focal lenghts (in pixels on the captor) '''[fx]''' and '''[fy]''', the coordinates of the principal point center '''[Cx]''' and '''[Cy]''' and the radial distortion coefficient (due to the quadratic calibration) '''[kc]'''. '''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. == '''Merging the images of several cameras:''' == == 3D calibration : == == 3D calibration with multiple planes: == The calibration of previous section provides 3D information thanks to the inclination of the calibration grid, but the precision is not optimum, and the process would not converge for a grid perpendicular to the line of view. A more precise procedure consists in first determining the intrinsic parameters by mutiple views of the same grid with different inclinations, as shown in the example **. with a corrects for 3D projection effects and gives some 3D indication. This is however made more precise by introducing different views of the same grid with different orientations, like shown in mages 1 to 5. The 3D options involve a full 3D calibration relying on the [attachment:3D_view.pdf pinhole camera model] (see [wiki:UvmatHelp#GeometryCalib] section 8.1). Once 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]'''. Durind the calibration, some intrinsic parameters are determined and shown in [Intrinsic Parameters] in '''geometry_calib'''. These are the focal lenghts (in pixels on the captor) '''[fx]''' and '''[fy]''', the coordinates of the principal point center '''[Cx]''' and '''[Cy]''' and the radial distortion coefficient (due to the quadratic calibration) '''[kc]'''. Now 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. == '''Merging the images of several cameras:''' == {{The previous calibration corrects for 3D projection effects and gives some 3D indication. This is however made more precise by introducing different views of the same grid with different orientations, like shown in mages 1 to 5. z position}}