Plate solving with error greater than 15 degrees

[garyhawkins]

I ran into a problem with plate-solving last night. If the target was greater than 15 degrees in error, the ASTAP plate solver called from SharpCap did not seem to switch to searching the whole sky after initially trying within 15 degrees. Instead, once the search reached 15 degrees it stopped and reported 'solution not found.' If I saved the image and used ASTAP directly to solve, a solution was found when the settings allowed for a larger search radius. I then tried installing All Sky Plate Solver, and it appeared this was stopping after it got to the 15 degree mark. The image also solved Astrometry.net.

Any thoughts on why neither tool appeared to go into extended search mode after a 15 degree search window was reached?

[admin]

Hi,

the behaviour of the 'plate solve and resync' tool (either from the tools menu or the button in the telescope controls) is to fix small(ish) errors in pointing and get the target into the middle of the field of view. To do this quickly, the search area is restricted to 15 degrees... If the mount co-ordinates are more than 15 degrees out then you don't have a small error in alignment, you have a large one!

If you want to do a plate solve over the whole sky, use the 'plate solve only' option from the tools menu. This will search the whole sky (although it uses the current mount location as a starting point). However, it takes no action with the results of the plate solving, it just displays them in the notification bar (and enabled tools like annotation once it has succeeded).

Hope this helps,

Robin

[garyhawkins]

Hi Robin,

Yes, it was a large error for sure. My remote mount kinda forgot where it was, and being remote, and with no way to do a local realignment, the restriction on a 15-degree search was not allowing me to gain control of the pointing. In the end, I had a friend drive over to the mount and do a traditional alignment. That got the pointing back in the ballpark, and plate-solving is working again.

All that being said, as ASTAP does an outward spiral search, would I be correct in saying that search times would not increase if the 15-degree restriction was increased?

Best regards,

Gary

[admin]

Hi Gary,

you're right that Astap does do a spiral outwards, so if a plate solving operation is going to work then it won't get slower due to a larger limit. However the problem comes in situations where the plate solving is not going to work on that image. A full sky search takes 50 to 100 times longer to fail than a 15 degree search, and getting that feedback that it didn't work quickly is valuable. In fact doubly valuable for Astap as SharpCap can end up running it twice - once in a 'use the image scale that worked the last time' mode and once in a slower 'try all possible image scales' mode if the first try failed.

Anyway, given your remote setup, I suspect that a 'Plate Solve Only' that reads out the co-ordinates would have let you re-do the sync either via the ASCOM driver setup page, or via the SharpCap scripting console with a command like

Code: Select all

# Syncs to RA=1.23 hours, Dec = +4.56
SharpCap.Mounts.SelectedMount.SyncTo(1.23, 4.56)

cheers,

Robin

[garyhawkins]

Thanks, Robin for that additional information.