Park before flipping and a delay before plate solving


#1

I have a couple of request that I feel would improve SGP.

1 Temporary park before a flip.
I don’t have a pier and I find that the camera or the camera cables come into contact with the leg of the tripod before reaching the meridian and way before a flip will be done with my 102mm scope. If there was an optional temporary park option before a flip, it would then be possible to park the scope for 15-20 min before a flip avoiding a contact with the tripod. As it stands now I cannot use the flip function with my 102mm scope.
2 Delay after slew while plate solving
I think a short delay after slewing and before SGP takes an image for the puporse of plate solving would be of great benefit. I often get streaks in my plate solve images and it throws platesolve2 off. A 1 or 2 second delay would avoid that from happening.

Thanks for the great work you do on SGP. It is an amazing program!


#2

Hi Stephan,

The standard solution to this would be to use a tripod extension.

Please have a look at this setting:

Regards,
Horia


#3

Fixing this in software would be quite an effort. It needs a parameter that specifies the furthest the mount can slew before the flip and a parameter that specifies the earliest the flip can be done.
When the mount is going to reach the first position before the end of the next exposure the pre flip processes need to be done, maybe collecting an image and solving it to get a reference position for after the flip. Then the mount needs to be paused - tracking off and guiding off.
SGP then waits until the target is past the second position. When this happens it does the flip, either by dong a slew to the target or setting the pointing state. It then does the pre imaging processes, accurate centring and starting guiding as required, and finally starts imaging.

Wile this is a fair amount of work to implement it may have other benefits.

In this case the pre flip limit is set before the meridian and the post flip limit after, giving a zone where the mount can’t go but with a mount that can track past the meridian the pre flip limit may be set after the meridian, possibly by an hour, and the post flip limit at or even before the meridian. This gives a zone which can be reached with the mount in either pointing state.

It would also help with mounts that can’t track far past the meridian but must be past the meridian to flip. In this case the pre and post flip limits may both be set to a position just past the meridian. Short exposures may be OK but a long exposure would need the mount to pause until the target was sufficiently past the meridian before the slew was done.

Getting all this right would be tricky, there are a number of different cases to be handled, not least managing when things go wrong, and there could be significant UI and documentation issues.

Some of this is in place using a single pier flip position but having two limits could give more clarity and flexibility for everyone.


#4

Maybe a more simple time delay in minutes selected by the user?


#5

FYI ACP does exactly this when the telescope is on the west side. if the next exposure will cross the meridian (or the delayed meridian) ACP stops tracking and waits until the target is past the meridian. at that point it issues a slew which causes the mount to flip.

but i don’t think this would work with SGP because SGP always wants to slew where the telescope is pointing immediately before the flip, with the exact coordinates coming from a plate solve before the flip. IIRC ken & jared tried to remove this pre-flip solve at some point but it broke something else so it came back. if i understand it right, the pre-flip solve is to help ‘casual’ imagers who have framed something manually vs. having put in coordinates into a target. ACP of course requires you to specify the target RA/DEC so there is always a set of coordinates to slew to.

i can’t remember if ACP also has a “don’t flip unless it is safe on the east side” but since it supports meridian delays i guess as long as whatever east side obstruction exists is less than the west side, it’s taken care of by the meridian delay.

but regarding this concept in general, i thought you agreed with Ken & Jared a couple of years ago that the right solution was for ASCOM to export some new state, something like “minutes until unsafe in this state” or “minutes until safe in opposite state” that would make life much easier for control programs like SGP to implement the kinds of things that the OP is asking for.

rob


#6

The work that ACP has done to implement this is what I meant by ‘quite an effort’ it doesn’t come for free.

Yes there was a suggestion that ASCOM should have additional parameters, but nothing came of it. It’s going to be tricky to implement this because it really depends on application developers seeing a need for this and asking for it. Even if they do there will be the situation for some time - possible forever - the the existing situation must still be handled.


#7

The pre-flip solve was put back into place because “trusting the mount” turned out to be a very bad idea. What we did remove was the pre-flip sync.

I don’t believe we want to get all crazy and add in pier side limits into SGP. That could get tricky especially since at different declination you could potentially have different clearances. And I can already see that as a feature request…I just feel it. Maybe we could have a “Park for X minutes” that could be triggered after the normal meridian flip. I’ll have to think about this and I’m certainly not committing to it…just a thought.

Thanks,
Jared


#8

i guess what i’ve never understood about this is why you have to trust the mount. in the situation where you have a target with defined RA and Dec, just slew there and refine the pointing on the other side.

it’s good that the pre-flip sync is gone, though it did expose a rather nasty bug in several CP3 firmwares which would probably still be there if not for that sync.

i guess for my part i’ve always just figured out what the worst case limits are and used those limits. it’s probably more for mount control software to handle variable meridian delays as is the current situation with A-P.

true, i have had occasion to read the ACP source code… anyway too bad about those new parameters because to me they seem pretty useful for automated imaging in general.

rob


#9

In that case you don’t have to…but people often define a target then decide they don’t like how it’s framed, adjust the frame and then never update the target with the position and just click “Run Sequence”. In that case you’d come back to your original frame and then be made that SGP moved you. And a lot of people use SGP without ever creating a target with RA/Dec.

The safest option for SGP is just to center where the scope is pointed prior to the flip in all cases. No matter what you get back exactly where you were pointed.

Thanks,
Jared


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