ASAP is GREAT, except when it isn't

[Peter Miller]

Short version: Often when I run ASTAP in batch mode the ** plate solving** works extremely well and inserts WCS coordinates into the header of my FITS files. Occasionally, it fails completely or almost completely. I would expect that it would fail occasionally (after all, the sky is big and there are lots of stars), except for the fact that my images already have RA & DEC in the FITS header. I'm no mathematician (or astronomer) but it seems that ASTAP could do the calculations for WCS if it already knows the RA & DEC. With that "hint", ASTAP should be able to plate solve the image very quickly (unless the image is really crappy!) But, I am guessing that ASTAP does not read the RA & DEC in the FITS header (maybe because the "keys" for RA & DEC in the header Key:Value pairs has not been standardized for FITS files. (I'm just guessing here.)

Longer version: I am learning to do my own exo-planet transit analyses. WCS info is extremely useful for that purpose (almost necessary). I am learning AstroImageJ (AIJ). It has "built-in" plate solving using Astrometry.Net. That works exceedingly well (often when ASTAP does not). BUT, it is a "cloud service". So it uploads the image to a service which then solves the image (and AIJ then adds the WCS solution to the FITS header). However, I don't want to blast their server with 2,000 - 3,000 images of the same part of the sky over and over again to solve all of the images. I don't think they would appreciate that. If I could install the astrometry.net plate solver locally (and then somehow get AIJ to use it), I would do so. But, I have not been able to install the CLI version of their plate solver. The instructions are too complex for my "pea brain." Therefore, I turned to ASTAP and have been very pleased with it - except when it does not work.

My question: My FITS images already have RA & DEC in the FITS headers (in decimal form) using the keys FOVRA and FOVDEC. Each image is also accompanied with a JSON file that contains RA & DEC in both decimal and HMS, DMS format. Is there a way to tell ASTAP to use that information to plate solve & calculate the WCS info which can then be inserted into the FITS header?

[han.k]

Hi Peter,

RA & DEC in the header Key:Value pairs has not been standardized for FITS files

They are standardized.

Keywords FOVRA, FOVDEC are new to me. They are not standard. ASTAP reads already three or four different style keywords for RA, DEC.

Which program writes these images and can you share one sample image to look at? Attach it to a post here or give me a link to a FITS image uploaded to nova.astrometry.net. Then I can have a look to the FITS header.

Cheers, Han

[Peter Miller]

I am using the Unistellar eVscope 2 "smart" telescope. It takes the images and then I have to upload them to Unistellar. I then request my files, and they send me a link to download my FITS files. Don't ask me why they do it that way. (Maybe to "clear RAM" on the telescope, but I don't know.) I am attaching one of my images per your request.

[han.k]

Strange they use none standard FOVRA, FOVDEC keywords. Nobody is using them. There are no othet keyword for the celestial position as you already indicated.

What I would do is create a special ASTAP version for you which can read them. Just keep that version and use it.

I don't want to add these abnormal keywords to the standard ASTAP version.

I would also suggest you contact the supplier and ask them to add the standarized keywords for celestial position to the header in the long run. See for example these standards:

https://fits.gsfc.nasa.gov/fits_dictionary.html
https://cdn.diffractionlimited.com/help/maximdl/FITS_File_Header_Definitions.htm

Are you you using Windows or an other operating system?

Han

[han.k]

Here is a special Windows version which will read correctly FOVRA and FOVDEC:

http://www.hnsky.org/astap_setup.exe

It is not marked as such. It will be only available till I issue a new version. So keep it save stored somewhere. Tell me if this works for you.

Han