Changes between Version 3 and Version 4 of Tutorial/CorrelationImageVelocimetryOptimisation
- Timestamp:
- Jan 27, 2015, 2:48:43 PM (10 years ago)
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Tutorial/CorrelationImageVelocimetryOptimisation
v3 v4 20 20 The parameters '''[num_Dx]''' and '''[num_Dy] '''define the mesh of the measurement grid, in pixels. Reduce them to get more vectors, but keep in mind that the spatial resolution is limited by the size of the correlation box. 21 21 22 == '''FIX1''': 23 Select the ’'''FIX1'''’ operation, which eliminates some false vectors using several criteria. Use the default parameters.'''''' 22 == '''FIX1''': == 23 Select the ’'''FIX1'''’ operation, which eliminates some false vectors using several criteria. Use the default parameters.''''''''''' 24 24 25 == '''PATCH1''': 26 Select the ’'''PATCH1'''’ operation, to interpolate the vectors on a regular grid and calculate spatial derivatives. Choose the default value 10 for the smoothing parameter '''[!FieldSmooth]'''. You can later try different values, the smoothing effect increasing with '''!FieldSmooth'''. Keep the default values for the other parameters.'''''' 25 == '''PATCH1''': == 26 Select the ’'''PATCH1'''’ operation, to interpolate the vectors on a regular grid and calculate spatial derivatives. Choose the default value 10 for the smoothing parameter '''[!FieldSmooth]'''. You can later try different values, the smoothing effect increasing with '''!FieldSmooth'''. Keep the default values for the other parameters.''''''''''' 27 27 28 == '''CIV2:''' 28 == '''CIV2:''' == 29 29 Select the ’'''CIV2'''’ operation to improve the correlation results, using the information on local image deformation, provided by the previous knowledge on velocity spatial derivatives (calculated in patch1). Use a finer grid dx= dy=5 than for civ1. The spatial resolution can be slightly improved by decreasing the correlation box, using for instance Bx,By=(15,11). The shift of the search range is here given at each point by the prior estimate from Civ1, so that the search range can be optimized: choose [21,17] which provides a margin of 3 pixels on each side of the correlation box. Note that ’civ2’ corresponds to a new measurement from the images, the previous civ1 and patch1 operations being used only as an initial guess for the search of optimal correlations. 30 30 … … 32 32 Then select ’'''FIX2'''’ and ’'''PATCH2'''’ with the default parameters. 33 33 34 '''* Running the calculation''': Press '''[RUN]''' to run the calculation. The results are stored in a new subdirectory, CIV_1, so the previous results are not erased (you can also set the name of the subdirectory in the GUI, by the edit boxes '''[SubDirCiv1]''' and '''[SubDirCiv2]'''. The existing subdirectories are listed above. 35 36 The status of the calculation is displayed in a new window which refreshes automatically. Close it to avoid blocking of new Matlab operations. This status window can be opened again by pushing the button '''[STATUS]''' in the GUI '''civ'''. Do not close civ until the calculation is finished. 34 37 35 38 36 The parameters of a CIV computation are stored in a xml file with extension ..!CivDoc.xml created in the directory containing the velocity files. These parameters can retrieved, opening this xml file with the browser of the GUI '''civ'''. Then the image file itself needs to be opened (the select again the check boxes for the operations beyond civ1 hidden by default).
