As far as I am aware a true radial PSDF should be invariant under rotation
of the original image data.
However the rPSDF in Gwyddion doesn't seem to be invariant under rotation,
which I tested using Gwyddion's "rotate by arbitrary angle" feature
(Gwyddion v2.19 on WinXP).
>From what I can gather from the code, it seems to only include the FFT data
from the first quadrant only, ignoring the other 3 quadrants, hence the
change in rPSDF under rotation.
Specifically lines 2273-2274 & 2277 from:
http://gwyddion.svn.sourceforge.net/viewvc/gwyddion/tags/gwyddion-2.19/libprocess/stats.c?revision=10808&view=markup
<http://gwyddion.svn.sourceforge.net/viewvc/gwyddion/tags/gwyddion-2.19/libprocess/stats.c?revision=10808&view=markup>seem
to indicate that only the first quadrant is being used, ignoring the rest.
Thanks,
Owen
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