HFD Differences between astap.exe and astap_cli.exe
Stacking program, astrometric (plate) solver, fits file viewer
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I am attempting to put some automation into my accept/reject process for images taken during an imaging session. I downloaded the most recent version of astap_cli.exe. I am using a command like like the following:
C:\Program Files\astap\astap_cli.exe -f filename.FIT -analyse
The HFD sent to stdout is always greater than the HFD value if I open the file in astap and select Tools-Image (CCD) Inspector. I cannot explain the difference.
Further, the value in ASTAP is consistently higher than what is displayed by other tools.
If you could explain why ASTAP and ASTAP_CLI are different I would greatly appreciate it. And, if you could comment on why it would be different in other tools, that would be great too, although I certainly understand if it is not possible for you to comment.
I appreciate your help.
Tim.
Hello Tim,
There should be no difference. In ASTAP you can select extra stars and then it will detect down to SNR=10. The default is SNR>30.
ASTAP_CLI is default SNR>=30 but you can als specify SNR>10.
With a lower SNR the HFD tend to be a little lower because a small part of the star flux is hidden in the noise. For example with SNR>=30 you can measure HFD is 2.3 and with HFD>10 you could measured HDF=2.2
The HFD measurement has been checked with artificial stars and also for the sub pixel based algorithm is is difficult to explain why it should make mistakes.
I have compared it with several other programs and the is a lot of difference between them. But I'm pretty confident ASTAP is measuring correctly.
Have tried the option in pixel math2 "Create a test image" . Then you can see how it performs for high and low SNR values.
What are the differences you see between the two versions?
Han
Han:
Thank you for the help. Adjusting the SNR allowed me to tune the command line interface so that it was matching the GUI. I'm still not sure why they are different, but I'm working for now. I appreciate your help.
Tim