Changes between Version 7 and Version 8 of Tutorial/CorrelationImageVelocimetryOptimisation


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Timestamp:
Jan 27, 2015, 5:06:11 PM (6 years ago)
Author:
vaillant1p
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  • Tutorial/CorrelationImageVelocimetryOptimisation

    v7 v8  
    1010Once the image pair has been chosen, the main parameters are the size of the correlation box in both directions ('''[num_!CorrBoxSize]_1]''' and '''_2''') and the size of the search box, ('''[num_!SearchBoxSize_1]''' and '''_2'''), expressed in pixels. For each velocity vector, the correlation box is moved within the search box to optimise the image correlation between the two sub-images inside the correlation box. To allow for a displacement of d pixels, the search box size must exceed the correlation box by at least d+2 on both sides, so 2d+4. A systematic shift '''[num_!SearchBoxShift_1]''', and '''_2''', can be also introduced to minimise the search area in the presence of a mean flow.
    1111
    12 Select the '''[CIV1]''' check box so the corresponding parameters show  up. Improve the spatial resolution by selecting smaller correlation  boxes in the '''civ1''' menu, for instance '''[num_!CorrBoxSize_1, 2]''',to 19 and 13  (image pixels). This is possible because of the high density particl seeding. The use of a elongated box along ''x'' allows to optimize  the resolution in the direction ''y'', to deal with the strong vertical  shear.
     12Select the '''[CIV1]''' check box so the corresponding parameters show  up. Improve the spatial resolution by selecting smaller correlation  boxes in the '''civ1''' menu, for instance '''[num_!CorrBoxSize_1, 2]''', to 19 and 13  (image pixels). This is possible because of the high density particl seeding. The use of a elongated box along ''x'' allows to optimize  the resolution in the direction ''y'', to deal with the strong vertical  shear.
    1313
    14 The PIV operation is conveniently visualised by pressing the button '''[!TestCiv1]''' in the GUI civ. Then the image appear in a new GUI '''view_field''',  in which the mouse motion displays the correlation function, which  appears in a secondary window, see figure. The resulting vector is shown  as a line pointing to the correlation maximum. The corresponding  correlation and search boxes are shown in the image.
     14The PIV operation is conveniently visualised by pressing the button '''[!TestCiv1]''' in the GUI '''civ'''. Then the image appear in a new GUI '''view_field''',  in which the mouse motion displays the correlation function, which  appears in a secondary window, see figure. The resulting vector is shown  as a line pointing to the correlation maximum. The corresponding  correlation and search boxes are shown in the image.
    1515
    1616It is now possible to adjust the search range, using prior knowledge on extremal velocities, see histograms displayed by '''uvmat''' in pixel  coordinates. We introduce estimated bounds on each velocity component,  [min] to -2 and [max] to 6 for ’u’ and (-3, 3) for ’v’, and press the  button '''[Search Range]'''. The optimum search ranges and shifts (for the given correlation box) are  now displayed: [33 25] and [2 0] respectively.