RA DEC Coordinates In FITS Header

[JohnAstroFun]

Aloha All,

This is my first post and hope this question is in the right topic area!

Been using Sharpcap Pro now for a couple years for both polar align and imaging (and focusing), and love it, with ASI 1600 camera, C8 Edge (at both F/2 and F/7). I also use Stellarium for goto slews and SYNCS (no issues there). I have both ANSVR and ASPS installed, and I was able to do some successful 'test' plate solving inside the house during the day by using the "Folder Monitor Camera" technique in Sharpcap (which allows me to basically load a previously saved fits image into SharpCap) and then plate solve it.

However, I'm getting wrapped around the axle here, trying to figure out how the RA DEC coordinates actually get put into an image's FITS header? Previously, all my acquired images (exposed/taken in Sharpcap) was done with no ASCOM connection to my Mach 2 mount. Do the coordinates initially come from the mount (when connected to it), and then get inserted to the image's FITS header? And/Or do those coordinates in the FITS header get updated after an image was plate solved? And wasn't sure if we're talking about "WCS coordinates"

The reason I ask, is that it seems that ASPS is capable of pulling the coordinates out of a FITS image, which I think would speed up the plate solving process. I'm assuming that right now, my tests are just 'blind plate solving' which takes longer. Just trying to understand the entire process, and sorry for the long email !! Thanks in advance for any word of wisdom!! John PS: And I'll set everything to JNOW thanks

[admin]

Hi John,

yes, the co-ordinates come from your mount position at the time that the image was captured. Just doing a plate solve in SharpCap (via the tools menu) will have no effect on this, but doing a 'plate solve and sync' from the GPS button will - that's because it updates the mount co-ordinates to match the plate solving ones.

When SharpCap uses ASPS it will pass the mount co-ordinates across when you use the GPS button to make the search much faster. When you use the tools menu it doesn't pass the co-ordinates and also allows a search of the whole sky, which can take a lot longer. The tools menu option is really designed for use by those without an ASCOM mount.

hope this helps,

Robin

[JohnAstroFun]

Aloha Robin,

ok thanks! I think I understand and I had a feeling the mount was probably passing the coordinates to the FITS header. Just need a little time outside to go thru some of this!

Hey Robin, I got one more question and then I'll go away!

Like most everyone else, I'm stuck imaging the same object over multiple nights. So, if I have a FITS image from Monday night (with the coordinates in the FITS header), is there a way to load that image into Sharpcap on Wed night and then use that image to somehow re-center the same object (for more imaging [on Wed night])? To be on the safe side I park and power off the mount every night (otherwise I'm thinking a subsequent goto to the same object would be very close)

This assumes the camera hasn't been touched or rotated and the mount hasn't been touched (ie it still has the same polar alignment between both nights). Was just wondering if there was a way to power everything back up, use Stellarium to do a goto (to the same object), and then re-use an image (from Monday night) in Sharpcap (to re-center the same object). No big deal either way, was just more curious than anything else and manually re-centering an object is no big deal.

Thanks again and thanks for those GREAT you tube videos (on gain and light pollution)!! John

[admin]

Hi John,

there isn't a way built into SharpCap to automatically go back to a previous image (although I do have that idea in my list of possible new features). What you can do is plate solve a previous image in your plate solving application (or on http://nova.astrometry.net for that matter), then tell your mount to go to the co-ordinates. Once that's done, do a 'plate solve and resync' in SharpCap and you should end up back in the same place.

SharpCap 4.0 will also have a 'click to recenter' option once you have used plate solving - basically put any part of the image in the center easily.

cheers,

Robin

[JohnAstroFun]

Aloha Robin,

Got it , thanks! Didn't think about doing it that way and hope you have a great weekend!

John