Changes between Version 10 and Version 11 of Tutorial/AdvancedParticleImagingVelocimetry


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Timestamp:
Jan 15, 2015, 4:29:43 PM (10 years ago)
Author:
vaillant1p
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  • Tutorial/AdvancedParticleImagingVelocimetry

    v10 v11  
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    99== Geometric calibration ==
    10 We know that the box width is 58.8 cm while the box height is 55.1 cm. This provides a simple method of calibration by pointing the four corners with the mouse. Open GeometryCalib by the upper bar menu Tools/geometric calibration. Activate the zoom, zoom on on the first corner, then desactivate the zoom to allow for mouse selection on the corner. Move on the other corners by the key board arrows and mark them with the mouse. Then you can see the image coordinates of the four points in the table of the GUI geometry_calib. Complement the table by the corresponding physical coordinates [0 0],[58.8 0],[58.8 55.1],[0 51.1] (choosing the lower left corner as coordinate origin). Then press APPLY with the simplest option 'rescale'. The quality is not excellent, with an error of about 3 pixels. The quality is improved by selecting the option 'linear' which accounts for a small rotation of the image with respect to the box (error about 1 pixel).
     10We know that the box width is 58.8 cm while the box height is 55.1 cm. This provides a simple method of calibration by pointing the four corners with the mouse. Open '''!GeometryCalib''' by the upper bar menu '''Tools/geometric calibration'''. Activate the zoom, '''zoom on''' on the first corner, then desactivate the zoom to allow for mouse selection on the corner. Move on the other corners by the key board arrows and mark them with the mouse. Then you can see the image coordinates of the four points in the table of the GUI '''geometry_calib'''. Complement the table by the corresponding physical coordinates [0 0],[58.8 0],[58.8 55.1],[0 51.1] (choosing the lower left corner as coordinate origin). Then press '''APPLY''' with the simplest option 'rescale'. The quality is not excellent, with an error of about 3 pixels. The quality is improved by selecting the option 'linear' which accounts for a small rotation of the image with respect to the box (error about 1 pixel).
    1111
    1212== Create mask ==
    … …  
    1414== Global PIV ==
    1515== PIV in two subregions ==
    16   The PIV computation is launched from the GUI 'civ', opened from uvmat by the upper bar command '''[RUN/PIV/CIV]'''. This GUI can be also directly opened by typing 'civ' in the Matlab command window, and the input  image file then opened by the upper bar command '''[Open/Browse]''', like in the GUI uvmat. The name CIV means Correlation Imaging Velocity to stress that the method relies on image correlations, which detect the displacement of image textures, not necessarily from particles.
     16  The PIV computation is launched from the GUI ''''civ' ''' opened from uvmat by the upper bar command '''[RUN/PIV/CIV]'''. This GUI can be also directly opened by typing 'civ' in the Matlab command window, and the input  image file then opened by the upper bar command '''[Open/Browse]''', like in the GUI uvmat. The name CIV means Correlation Imaging Velocity to stress that the method relies on image correlations, which detect the displacement of image textures, not necessarily from particles.
    1717
    1818The PIV operation depends on many parameters, but the default values proposed by the GUI provide a good first approach in many cases. Press '''[RUN] ''' to get the result. The button is then colored in grey until the computation is finished. The operation produces a  file with format netcdf, extension '''.nc''', in a subdirectory called ''''CIV' ''' by default. The file name ends with index string '_1-2' indicating that it results from images 1 and 2. The file name and its status is indicated in a new figure '''civ_status'''. Press the file name to open it with uvmat, or use the browser of '''uvmat'''.