Changes between Version 20 and Version 21 of Tutorial/AdvancedParticleImagingVelocimetry2

Jan 15, 2015, 4:39:37 PM (9 years ago)



  • Tutorial/AdvancedParticleImagingVelocimetry2

    v20 v21  
    66Open the example UVMAT_DEMO6_PIVconvection (accessible on
    8 = calibration =
     8= Calibration =
    99Perform the geometric calibration by marking the four box corners with the mouse, as described in [wiki:"Tutorial: geometric calibration" Tutorial: geometric calibration], section 'calibration with reference points'. Alternatively, you can skip this operation by using the reference file Dalsa1.ref.xml provided, removing the extension '.ref' to make it active.
    11 = mask =
     11= Mask =
    1212Open the original image with uvmat, selecting the transform option 'phys'. Create a mask polygon by the menu bar command Projection object/mask_polygon. Set the option 'mask_outside' and introduce the coordinates of the four corners in '''Coord''' (like for geometry calib). Plot the polygon. Then create the corresponding mask by '''Tools/make mask'''. The default name is 'mask_1.png' in the subfolder Dalsa1.mask.
    14 = sub_background =
     14= Sub_background =
    1515We observe parasitic light rays on the images which correspond to fixed features, leading possibly to spurious velocity vectors equal to 0. To eliminate those we use sub_bacground.
    1616Open the image with 'series' and select the program 'sub_background'. This function is not provided in the default menu, so you need to use the last menu option 'more...', and select the function in the sub-folder 'series/' of the package uvmat. This option is then preserved in the menu for later use.
    1717Then run sub_background over the whole index range in i and j, using the default parameters. Answer Yes to the question 'apply levels', which will conveniently rescale the image brightness after background removal.
    19 = first PIV =
     19= First PIV =
    2020Do PIV  on the the whole image series, selecting all the options from Civ1 to Patch2 (see [wiki:"Tutorial: Particle Image Velocimetry" Tutorial: Particle Image Velocimetry] for an introduction).
    2626Looking at the results with uvmat, we global flow fetures. We notice hower that the thin parietal plume is not properly resolved while the precision in the interior is poor because of the small displacement within the frame pair. So the next step will be to perform two PIV series optimized for each sub-region and merge them.
    28 = making two masks =
     28= Making two masks =
    2929The parietal jet requires a very good resolution, particularly among x. To limitate PIV to this jet, let us create a specific mask.
    3030Open the previously created contour polygon contour_mask.xml in uvmat  by the menu bar '''!Tools/Projection object/browse...'''. Check the box '''edit''' (tag '''[!CheckEditObject]''') in the frame '''Object''' of uvmat (right hand side) to allow editing of the polygon. then replace the lower x bound 0 by 52. Then create the corresponding mask by '''Tools/make mask''', save it with name Dalsa1.mask/mask_plume.png. Similarly create a mask for the bulk Dalsa1.mask/mask_bulk.png, with bounds in x [0 55].
    4343Select the pair j=1-3 to deal with the small velocities (considering that the parietal plume has been masked). Then use the default parameters.
    45 = merging data on a common grid =
     45= Merging data on a common grid =
    4646create a projection grid in phys coordinates. For that open a velocity field with uvmat, displayed in phys coordinates. Use the upper bar menu option Projection object/plane. Then in the GUI '''set_object''', choose the option !ProjMode=interp_lin. Choose a mesh 0.1 cm in each direction, ranging from 0 to 58.8 in x and 0 to 55 in y. Press REFRESH to see the result of projection in the GUI view_field. Check the option '''nb_vec/4''' to reduce the number of vectors displayed on the plot.
    5252It is also advised to introduce masks in the interpolation process so that each field is interpolated in its range of validity. This is done by selecting the option '''Mask'''. Use the browser to fill the table of masks, in accordance with the table of input file series.
    54 = merging data using thin plate shell =
     54= Merging data using thin plate shell =
    5555The previously used linear interpolation does not provide field derivatives. For that purpose, we proceed as previouisly but use the option '''!ProjMode''' ='interp_tps' for the projection plane in '''set_object'''.