Setting interrogation window to bottom of images

[Alexandra Stephens]

Hi PIVlab folks,

I am working with images taken at a boundary layer such that the edge of the BL is the bottom of the image. I want to ensure that the bottom edge of the bottom-most interrogation window lines up with the bottom edge of the image, so that if any pixels must be excluded, they would be at the top of the image. For example, an image that is 3000 pixels tall with 64x64 px interrogation windows would have 46 interrogation windows in the vertical direction, with 56 pixels that are neglected (3000 - 46*64 = 56). I want to be sure that those 56 pixels are at the top, and not the bottom, of the image. Is there a way to do this in PIVlab? When I have determined the ideal subwindow size I will just crop the images in pre-processing, but my datasets are very large (300+ GB), so I want to avoid doing this until I am set on a subwindow size.

I'm guessing I could just rotate the images by 180 degrees, but I'm trying to avoid doing this because of the quantity of data I have to analyze, so limiting pre-processing time would be ideal.

Thank you!

Alexandra Stephens

[thielickeoptolution]

Dear Alexandra, PIVlab will always center the interrogation areas, so that gaps at the borders are symmetrical. I don't know an easy way to achieve what you want. I think you have to choose a final interrogation area, and then pad your original image via trial and error until the interrogation area lines up correctly.