Changes between Version 18 and Version 19 of Tutorial/ParticleImageVelocimetry


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Timestamp:
Jan 15, 2015, 4:14:28 PM (6 years ago)
Author:
vaillant1p
Comment:

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  • Tutorial/ParticleImageVelocimetry

    v18 v19  
    9393This can be avoided by using a mask, which is an image of the same size as the images used for PIV. Grey color in the mask indicate regions excluded from measurement.
    9494
    95 To produce the mask, first create a polygon by the menu bar command [Projection object/mask polygon]. Draw the mask with the mouse by moving around regions to exclude. Left mouse button to initiate the plot and produce new boundary points, press right hand button to finalise the polygon. By default mask is set inside the polygon, but it can be made outside by selecting the option ’mask_outside’ in the menu [!ProjMode] of the GUI set_object.
     95To produce the mask, first create a polygon by the menu bar command '''[Projection object/mask polygon]'''. Draw the mask with the mouse by moving around regions to exclude. Left mouse button to initiate the plot and produce new boundary points, press right hand button to finalise the polygon. By default mask is set inside the polygon, but it can be made outside by selecting the option ’mask_outside’ in the menu '''[!ProjMode]''' of the GUI '''set_object'''.
    9696
    97 Then the mask itself is produced by the menu bar command (!Tools/Make mask]. The corresponding image is then displayed and stored by default in the directory of the initial image. Note that if several mask polygons have been initially created, as listed in [!ListObject] (bottom right of the GUI uvmat), they will be merged as dark regions in the resulting mask (useful in case of multiple ’holes’).
     97Then the mask itself is produced by the menu bar command '''[!Tools/Make mask]'''. The corresponding image is then displayed and stored by default in the directory of the initial image. Note that if several mask polygons have been initially created, as listed in '''[!ListObject]''' (bottom right of the GUI uvmat), they will be merged as dark regions in the resulting mask (useful in case of multiple ’holes’).
    9898
    99 The mask image can be seen as a mask by selecting [view_mask] at the upper left of the GUI uvmat. For checking purpose, it can be also opened by the browser of uvmat like any image. In the GUI civ, the mask is introduced by the selecting the green check box [Mask]. Vectors under the mask are not calculated in the resulting velocity data.
     99The mask image can be seen as a mask by selecting '''[view_mask]''' at the upper left of the GUI '''uvmat'''. For checking purpose, it can be also opened by the browser of '''uvmat''' like any image. In the GUI '''civ''', the mask is introduced by the selecting the green check box '''[Mask]'''. Vectors under the mask are not calculated in the resulting velocity data.
    100100
    101101= Refined PIV =
    102102
    103 To improve the results, come back to the GUI CIV , and follow these successive steps, corresponding to a sequence of operations.
     103To improve the results, come back to the GUI '''CIV''', and follow these successive steps, corresponding to a sequence of operations.
    104104Optimizing the Civ1 parameters
    105105
    106 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 [Bx],[By] to 19 and 13 (image pixels). This is possible because of the good image quality and high particle density. The use of a smaller box in y allows to optimize the resolution in this direction, to deal with the strong vertical shear. It is now possible to adjust the search range, using knowledge on extremal velocities, see histograms displayed by uvmat in phys 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 are now displayed. In consistency with higher resolution, we set the grid mesh to [Dx] and [Dy] to 10. Finally select the Mask option : the mask name should be displayed in the corresponding edit box, else a browser leads to the appropriate mask file.
     106Select 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 [Bx],[By] to 19 and 13 (image pixels). This is possible because of the good image quality and high particle density. The use of a smaller box in y allows to optimize the resolution in this direction, to deal with the strong vertical shear. It is now possible to adjust the search range, using knowledge on extremal velocities, see histograms displayed by '''uvmat''' in phys 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 are now displayed. In consistency with higher resolution, we set the grid mesh to [Dx] and [Dy] to 10. Finally select the '''Mask option''' : the mask name should be displayed in the corresponding edit box, else a browser leads to the appropriate mask file.
    107107FIX1
    108108