DynamicPSF and Rotation Ambiguity

[jeffweiss9]

Hi, I've been trying to use the neat new DynamicPSF process to analyze my subs but discovered that it doesn't recognize that rotations that are ~180 degrees apart really should be treated as the same rotation angle.  My star list, for example is coming back with half at ~0 degrees and the other half at ~180 degrees so I get an average rotation angle (Sigma button) of ~90 degrees. 
Thanks,
-Jeff

[jeffweiss9]

I noticed that Juan partially addressed this issue in response to Howard's reporting also of two clusters of rotation angles near 0 and 180 degrees, respectively, in the DynamicPSF discussion thread:

http://pixinsight.com/forum/index.php?topic=3261.30

  I also have aspect ratios of around 0.88 in the subs I've been trying to analyze.  After reading the posted response, however, I still thing taking the average of the 0 and 180 values to report an average rotation of 90 degrees should/could be avoided by the algorithm rather than having to throw out half the stars to get a sensible answer.  The average PSF itself, when exported for deconvolution, however, doesn't have any ambiguity, so it is only a 'nice-to-have' if all the stars could be used in DynamicPSF to get valid average values for characterization of the subs.  But it would be good.
Thanks,
R/Jeff

[Nocturnal]

Hi Jeff,

it seems that angles 0 and 180 could be different if the weight of the star is not centered in the oval. Perhaps this is addressed somewhere already but I didn't recognize it as such.

[Juan Conejero]

Hi Jeff and Sander,

PSF rotation angle refers to the major axis of the fitted ellipse and is measured counter-clockwise with respect to the positive X-axis direction and the star's centroid.

For example, two rotation angles of 3 and 177 degrees denote different star orientations, which can be either very close or very far away each other, depending on how we interpret them. One obvious solution to achieve what you want would be showing them as +3 and -3 degrees, that is, measuring rotation angles in the ]-90,+90] range instead of [0,180[. I could add this as an optional feature to DPSF in the next version, perhaps enabled by default. What do you think?

[jeffweiss9]

Juan-
 Sounds great. Looking forward to it.
-Jeff