Changes between Version 122 and Version 123 of UvmatHelp


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Timestamp:
Dec 7, 2014, 6:51:40 PM (6 years ago)
Author:
sommeria
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  • UvmatHelp

    v122 v123  
    574574The 3D options involve a full 3D calibration relying on the [attachment:3D_view.pdf pinhole camera  model]. The method was first proposed by R.Y. Tsai, 'An Efficient and Accurate Camera Calibration Technique for 3D Machine Vision'. Proceedings of IEEE Conference on Computer Vision and Pattern Recognition, Miami Beach, FL, pp. 364-374, 1986). We use a more recent version, with the toolbox [->http://www.vision.caltech.edu/bouguetj/calib_doc/] . 3D calibrations are done in two steps. The camera'' intrinsic parameters'', which are the focal length and the quadratic deformation coefficient, are first determined by different views of the same grid observed at different angles. Then the ''extrinsic parameters'', which represent the rotation angles and translation of the physical coordinates with respect to the camera, are obtained with a single image of the grid positioned in a known plane $z=cte$. The option 3D_extrinsic allows the user to do only the second step from known intrinsic parameters. Those depend only on the camera with its objective lens and focus adjustement. Note that these 3D options require a calibration grid, with a sufficient number of calibration points covering the whole image.
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    576 The transform coefficients for each image series are stored in the corresponding XML documentation file <!ImaDoc>, described in [https://servforge.legi.grenoble-inp.fr/#ImaDoc section 3.5],  under the tag <!GeometryCalib>. Calibration creates an xml file, or updates an existing xml file <ImaDoc>, with the name of the DataSeries folder containing the images currently opened by uvmat, followed by the file extension .xml. If a new data series is produced in a folder named with an extension, for instance DataSeries.civ for PIV, the xml file DataSeries.xml is still used, except if a new xml file DataSeries.civ.xml also exists.
    577 
    578  Calibration coefficients  can be displayed with the GUI '''geometry_calib.fig''' described below. Field transform from pixel to physical parameters is performed by the function ''phys.m'' in UVMAT/transform_field, which calls the pointwise transform functions  ''phys_XYZ.m'' (from image to physical coordinates) and ''px_XYZ.m'' (from physical to image coordinates), as well as ''phys_ima.m'' which transforms images. When an image or PIV velocity field is opened by uvmat, the transform function 'phys' is automatically loaded as described in [#a4.6Fieldtransforms section 4.6].
     576The transform coefficients for each image series are stored in the corresponding XML documentation file <!ImaDoc>, described in [#ImaDoc section 3.5],  under the tag <!GeometryCalib>. Calibration creates an xml file, or updates an existing xml file <!ImaDoc>, with the name of the !DataSeries folder containing the images currently opened by uvmat, followed by the file extension .xml. If a new data series is produced in a folder named with an extension, for instance !DataSeries.civ for PIV, the xml file !DataSeries.xml is still used, except if a new xml file !DataSeries.civ.xml also exists.
     577
     578Calibration coefficients  can be displayed with the GUI '''geometry_calib.fig''' described below. Field transform from pixel to physical parameters is performed by the function ''phys.m'' in UVMAT/transform_field, which calls the pointwise transform functions  ''phys_XYZ.m'' (from image to physical coordinates) and ''px_XYZ.m'' (from physical to image coordinates), as well as ''phys_ima.m'' which transforms images. When an image or PIV velocity field is opened by uvmat, the transform function 'phys' is automatically loaded as described in [#a4.6Fieldtransforms section 4.6].
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