Hi Hans,
PI generally doesn't care about the aspect ratio of your images but I can imagine there's a chance that wavelet based processing may produce a different result depending on whether the image was resized before or after.
- resample to square the image
- wavelets
vs.
- wavelets
- resample to square
You could try this yourself to see. I think the decision you need to make is whether you resample as the first or final step in PI. Generally I'd say resample as late as possible but given scale based processing with wavelets it may be better to resample first.
Judging by your name you're probably Dutch so perhaps the expression 'lead or old iron' 'lood om oud ijzer' means something to you. In other words it probably doesn't matter.
That said I had non-square pixels (DSI) and I'm glad they're square now. Star registration works much better for starters.
