Eccentricity = 0 in Subframe Selector

[smccully]

https://www.dropbox.com/s/muycy83gm1ggzik/Lum-1x-120s-29_c.xisf?dl=0

https://www.dropbox.com/s/i0ns8sogph5o7hf/Lum-1x-120s-25_c.xisf?dl=0

[pfile]

that's something else then - your screenshot is of the SFS process, not the script.

anyway clearly something is wrong here - juan would have to take a look - i know that the new StarAlignment module does all sorts of stuff with PSF fitting so it could be that both the SFS script and SFS module need updates to take this into account.

rob

[smccully]

Yeah, this was always working and then even prior to the recent 1.8 update it stopped working. So i am not sure its actually related to the rework, though i really dont know

[dkuchta5]

smccully: Good to know.  I checked a friend's installation on Windows and he was getting good eccentricity numbers, and it works for me on my Windows laptop.  So I figured it was just a Mac issue.  Not so, I guess.  I wonder if it has something to do with the individual computer configuration. 

-Dan

[smccully]

I dont know, this was working. No idea what if anything really changed when it stopped working. But it hasn't worked since, even after reinstallation for latest version

[Geoff]

It’s not only eccentricity that is a problem.  An FWHM less than one arc second is not believable unless you are imaging somewhere in the high Andes.

[Juan Conejero]

It’s not only eccentricity that is a problem.  An FWHM less than one arc second is not believable unless you are imaging somewhere in the high Andes.

I have just measured the two frames linked above with SubframeSelector, and the FWHM values reported are 3.3 and 3.6 arc seconds, respectively for the 25_c and the 29_c frames. I have used a frame scale value of 0.4"/px and a circular Gaussian PSF, just as shown on the screenshot. These FWHM values are quite correct IMO.

It is true that eccentricities are being reported as zero for both frames; I'll investigate this later. As for FWHM, something looks wrong with the measurements being shown here. Can you please upload this entire set of M33 frames?

[dkuchta5]

>> I dont know, this was working. No idea what if anything really changed when it stopped
>> working. But it hasn't worked since, even after reinstallation for latest version.

My experience exactly.  Installing the latest version did not change the behavior.
-Dan

[smccully]

It’s not only eccentricity that is a problem.  An FWHM less than one arc second is not believable unless you are imaging somewhere in the high Andes.

I have just measured the two frames linked above with SubframeSelector, and the FWHM values reported are 3.3 and 3.6 arc seconds, respectively for the 25_c and the 29_c frames. I have used a frame scale value of 0.4"/px and a circular Gaussian PSF, just as shown on the screenshot. These FWHM values are quite correct IMO.

It is true that eccentricities are being reported as zero for both frames; I'll investigate this later. As for FWHM, something looks wrong with the measurements being shown here. Can you please upload this entire set of M33 frames?

https://www.dropbox.com/sh/n6rp6090dq7k67k/AAADSR7IZI0fkdAth-ASM9aea?dl=0

[Juan Conejero]

Thank you for uploading the images. I have no problem at all to measure them with the current version of the SubframeSelector tool.

If you force measurements of circular PSFs, then eccentricity has to be zero. Eccentricity is defined as:

sqrt( 1 - (sy/sx)² )

where sy and sx are the standard deviations of the fitted PSF function on the vertical and horizontal axes, respectively, and sx >= sy conventionally. In the circular case we have sx = sy, so eccentricity is equal to sqrt( 0 ) = 0. So this is the expected behavior.

[Juan Conejero]

See the enabled Circular PSF parameter in your screenshot.

[dkuchta5]

And we have a winner!   Thank you, Juan !!!

I checked in the Script under the Star Detection and Fitting panel and sure enough, the circular PSF was checked. I have no memory of changing that.  In fact I never change anything in that panel.  I wonder if the default got changed in some release?

Anyway, it works now.  Thanks again!

-Dan

[Juan Conejero]

And we have a winner!   Thank you, Juan !!!

Now you owe me a virtual beer!