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I made a blank 512 x 512 image. I added four psf's near the corners.Using default settings, I used imshift to shift the psf's by 0.5 pixels in x and y.
The psf structure was preserved but daofind told me I shifted the psf's 0.553 pixels.I then used geomap and geotran to remove the shift. Geomap told me the shift between the two images was equal to what daofind told be but geotran was off by about 0.05 pixels when fixing the image and all structure in the psf was lost.Questions. Do you have recommendations for what type of interpolation to use for imshift?
Can I get geotran to perform better?Thanks.

Hi,I'm not sure what you are doing exactly. There will always be some difference because how daofind centroids may not be tuned exactly to match what you added or how the interpolation was done. However, it does sound like there is some possible parameter problem.To answer your questions, I think poly5 is the interpolator you should use with imshift. You could use a more sophisticated method like sinc but the PSF has to be reasonably sampled in this case.Are you doing this with noise added by the way? If not then there might be some artifacts from the artificial edge of the added PSF and sensitivity to low level ringing of the interpolators.Again, if you want to give me enough details that I could reproduce what you did I could give you more guidance.Yours,
Frank Valdes

Thanks, I've been pulled away from this for awhile. I may take you up on your offer later.