New Tool: DynamicPSF

[Hans Pleijsier]

Juan wrote:
//In a nutshell: you click on an image and DynamicPSF looks for a star (or a star-like object) around the coordinates you have clicked at.//


On a macbook this translates to a double-click on the trackpad and that is what came back to me 2 seconds ago.

Juan, please disregard this issue.
 
HP

[jeffweiss9]

I just moved this from elsewhere to this New Tool: DynamicPSF thread since I see the subject of rotation angles 180 deg apart is being discussed.  I don't I agree with the conclusion above that this just concerns a a few outliers at least for my data that may not be the highest SNR.   IMO, the problem is the fundamental degeneracy in the elliptical representation that is causing my population of stars to split roughly equally between near zero and near 180 degrees rotation angle.  Perhaps it would help for DynamicPSF to also report (with any noncircular option) the 'relative rotation angle' for each fit WITH RESPECT TO THE MAJOR AXIS OF THE ELLIPSE which would then be a more consistent and meaningful measure with which to discard outliers, even in the context of the 180 degree ambiguity in the rotation angle of the major axis itself.   But I think some scheme might also be devised to resolve the 180 degree ambiguity (due presumably, as Juan suggests, to the randomness in the initial star detection location) in the major axis.  That would probably be more complicated; perhaps, some kind of clustering algorithm to identify a single major axis (same sign rotation angle) out of all the reported axes from the individual fits.
   The following probably belongs on the wish list topic, but what I'd really like beyond fixing this degenerate sign-of-the-rotation angle problem is another layer that would analyze subs (better, multiple subs) to generate maps of FWHM (curvature), aspect ratio, etc. to provide detailed analysis of image quality -- plus maybe a sorter that ranks subs in terms of those qualities. That would be a very useful addition, IMHO.
Clear skies,
-Jeff

[Juan Conejero]

Hi Jeff,

IMO, the problem is the fundamental degeneracy in the elliptical representation that is causing my population of stars to split roughly equally between near zero and near 180 degrees rotation angle.

As noted in your bug report, the solution to this problem is to represent PSF rotation angles in the ]-90,+90] range, instead of [0,180[. This will be available as an optional feature (enabled by default) in the next version of DynamicPSF (due this week, along with other updates).

another layer that would analyze subs (better, multiple subs) to generate maps of FWHM (curvature), aspect ratio, etc. to provide detailed analysis of image quality -- plus maybe a sorter that ranks subs in terms of those qualities. That would be a very useful addition, IMHO.

I agree completely, and in fact I had all of these tasks in mind when I wrote DPSF. This is a nice work to be implemented as a script (or a collection of scripts). It is quite easy because since PI version 1.7.0 processes provide output data that can be retrieved from JavaScript code. I'll explain this on the software development board.

[jeffweiss9]

Hi, Juan-
 Just great.
And thanks.
-Jeff

[jeffweiss9]

Hi, Juan-
  A question on interpretation of star FWHM (again for image characterization rather than PSF generation):  On my subs, the FWHM's from the Moffat form tend to be an arcsecond or so larger than those using the Gaussian form,  Since the Moffat gives a better fit (lower average MAD), am I right to assume that it is also providing a more accurate measurement of FWHM?   I'm presuming the FWHM calculation is, in both cases, finding the width of the region where the fitted function falls to half-height, but wonder if the longer tails on the Moffat function (beta~2) are just "pinching in" the fits above half-height but that shouldn't really be considered the FWHM because of the longer tail.  I anticipate your response to just use the same form as a relative measure from sub to sub, but wonder if there is an absolute interpretation as to which is more accurate.
  Thanks.
-Jeff

[sreilly]

I've just started trying to use this tool and am getting nowhere fast. I have a single 20 minute image of M31 open and it has been calibrated and a histogram stretch applied. With the DynamicPSF tool open I can't get any stars selected. I'm clicking on stars but nothing shows in the tool. What am I doing wrong?

[Nocturnal]

Hi Steve,

how about if you look at the image in 1:1 mode and click right on a star? The first click will identify the view DPSF will work with. If that doesn't work then I recommend cropping a small section of your image and attaching it here in 32b format.

[sreilly]

Well that beats all. I remoted to my office computer and used the same image and that worked. I ended that session and tried it again on the laptop and again it worked. I have no idea what was different. It was done each time at full resolution. Oh well, it's not the first time I've stumbled!

Thanks again.