Changes between Version 9 and Version 10 of Tutorial/AdvancedParticleImagingVelocimetry2

Timestamp:

Aug 27, 2013, 9:26:12 AM (11 years ago)

Author:

sommeria

Comment:

--

Tutorial/AdvancedParticleImagingVelocimetry2

@@ -3 +3 @@
 
 = calibration =
-mark corners
+mark the four box corners with the mouse. We find ....
+The corresponding physical coordinates are known to be (0,0),(58.8,0),(58.8,55.1),(0,55.1), with an origin (0,0) taken at the lower left. Introduce those in the table ![ListCoord]. This can be conveniently done by copy paste of the Matlab vector x=[0 58.8 58.8 0] in the upper line of the x column, and y=[0 0 55.1 55.1] in the y column (use carriage return to validate the input).
+Then apply rescale. we observe that the figre is slightly rotated.
+We then apply linear which allows for rotation. The precison is improved. 
 
 = mask =
+Open the original image with uvmat, selecting the transform option 'phys'.  withCreate 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'''.
 
 = sub_background =
+We 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. 
+Open 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. 
+Then run sub_background over the whole index range in i and j, using the default parameters. Answer Yes to the quaestion 'apply levels', which will conveniently rescale the image brightness after background removal. 
 
 = first PIV =