Plate solve from "home"


When I start the night in the “home” position pointing to Polaris SGP fails to plate solve the initial position when the sequence starts to slew to a target. If I take a quick pic using frame and focus and then blind solve that image it will plate solve that fine. If I use stellarium and slew the scope to the target and then start the sequence from there it will plate solve just fine. I may get an error message sometimes Plate solve is too far off from the expected position of the mount


Plate solving pointing to Polaris has always been problematic. To avoid this problem just check both “Slew” and “Center” in the Target Settings dialog. This tells SGP to first perform the slew, then do the first plate solve at the destination. Its also much faster, since the source plate solve is not necessary. Works perfectly.


thanks I’ll give it a try


Am I missing something. ?? Have you already “synced” the mount to SGP by using the SGP module “Scope Centering” and “Solve and Sync” ?? That should be your first step . Than the plate solve and centering routine should not be a problem.


I’m not sure I follow my steps are:
use frame and mosaic wizard to create a sequence and use precision centering with plate solve
the mount is parked at “home” pointing to Polaris
unpark the mount
hit run sequence
SQP then takes a image and attemps to plate solve while looking at Polaris that’s when I get the plate solve is too far off

should I use the setting slew to target then center in the mosaic wizard when I create the sequence


in the target settings dialog, tick both “slew to target” and “center on target”. that will cause SGP to first slew to where the mount thinks the target is, then cause it to solve and sync to refine the pointing.

i don’t think this has to be done in the mosaic wizard, it can be done after the targets have been created. however you’ll have to open every target in the mosaic and tick these two boxes.

solving at the pole is actually pretty dangerous - if the solve is close but not correct, SGP may accept the solution… and then you might slew right into the pier. which is what happened to me the other night, quite by accident (user error for sure)


This is not really necessary or useful. By ticking both “Scope Centering” and “Solve and Sync” this first plate solve that occurs after the mount slews to the destination performs the required syncing of the mount. And as pfile says, the mosaic wizard is not related to any mount syncing when it is being created by the mosaic wizard. Only when actually running the mosaic sequences does mount syncing come into play. And definitely check both “Scope Centering” and “Solve and Sync” for all the targets the wizard creates.

As an aside, in a prior thread Ken suggested it might be a good idea to check both of these by default when new targets are created. I would favor this change.


OK…understood. However, seeing that the scope is not synced , the first slew could be quite a ways off from the target and require lots of centering attempts before it is successful. Also, if you are using planetarium software it will not be synced to the software. Now I am only talking about my “cheap” mount and a portable setup. LOL

I have found that syncing from the get go will get me synced with Stellarium quicker (or whatever). After that, my slews are very close to be centered and the centering routine is MUCH quicker. With a Mosaic it is only necessary to tick the Slew and Center with just the first panel. All other panels just the Centering is ticked.

I don’t see a “Solve and Sync” within the Wizard. Also, stay away from the Pole when solving and/or syncing.


The “Center on” option does a “Solve and Sync” of your scope:


Dennis, I see your point. But it looks like your first sync will also likely be way off and require several sync iterations.
In my case I have an obs and even if I have moved the scope by hand and have to realign it before a run, I am usually within a few hundred pixels on the first slew, and 1 or 2 more get me to less than the requested 20, usually around 5. If I have not manually moved the scope between sessions, it gets within less than 100 on the first slew. I also don’t use any planetarium software during the run, so that is not an issue for me.


here is the option I was talking about


Yes, that is generally the best option for most if not all targets, but ABSOLUTELY the first target. If your mount generally knows where it is (ie you’ve parked it or it knows that you’re at CWD when it starts up) then slewing first and then centering is generally best.

Plate solving at the pole can often make your mount “lose its mind”. It’s very difficult to determine where the mount is located at that position. It’s the same issue as Dobson’s Hole with Alt/Az mounts (so if you own an Alt/Az never sync at zenith :slight_smile: ) You can give yourself an idea of what the problem is by pointing at the pole and then just rotating in RA. If you have little to no cone error you’ll see that the center of the image remains unchanged and you’re just rotating around the center. So the coordinates are the exact same even though your RA could be 180 degrees away from where it started.

Hope that helps,


Thanks for everyone’s help