Enabling Early Meridian Flip on AP mounts

I would like to be able to do a meridian flip 1-3 hours ahead of the meridian with my AP1100 and APCC Pro. This lets me track an object further over my roof line. I set an earlier (negative) time for the meridian in APCC Pro and select Send Limit info to SGP, but the SGP Pro AutoFlip settings take it as a positive value, delaying the flip.

Hi @WayneH

From what I understand SGP does not allow the mount to flip until after it has crossed the Meridian. Not sure if this is any help and I don’t have a AP mount but use the Celestron mounts. In their NextStar+ H/C there is a feature for the Meridian to Favor East, Favor West or Disable. I sometimes use the Favor West, depending on the target location. I wounder if the AP mounts have something similar that might allow the mount to start out on the West side and no flip would be required. Just a thought.


blockquote, div.yahoo_quoted { margin-left: 0 !important; border-left:1px #715FFA solid !important; padding-left:1ex !important; background-color:white !important; } Actually I can do that and do it if it doesn’t run me into the pier. However, on some objects I have to wait for a while before I can flip to ensure I don’t hit anything. I’m hoping that they can add a feature to SGP to allow this with appropriate user control.


Just curious if you’re going to need to do a pier flip anyway is there an advantage of wanting to do the flip before the target crosses the Meridian? I was thinking for folks that want to do flips early, and if the target location permits without the mount running into the pier, was to get the flip out of the way before stating off the imaging sequence. Just one less thing to worry about and it might help when stacking and aligning images. must be another reason to flip early?


Ken and Jared will have to weigh in. i probably mentioned this in the other thread, but i think they were reluctant to add any kind of mount-specific code and were waiting for some enhancements to ASCOM - for instance, mount properties that could be queried like how long it’s safe for the telescope to be in the current pointing state, how long until it’s safe to be pointing at the same place from the other side of the pier, etc.

whether or not those things are really being discussed by the ASCOM developers is another question, but it did come up some months back and if i remember right @Chris was part of the discussion.


SGP can flip prior to the meridian if your mount supports setting Side Of Pier. This is something that the ASCOM driver would need to expose and is a standard ASCOM property. Many mounts like Losmandy, Taks, Celestron, and other support flipping prior to the meridian.

I’m not familiar with the AP driver but there may be reasons why this is limited. I believe APCC likes to handle flips and such on its own (which will likely be problematic with SGP).


Thanks Jared,

I’ll check with Ray Gralak at AP on the Side of Pier question, I know it has the info as it displays it during operation. In a recent APCC release, it includes a “Send limit info to SGP” checkbox, but it appears SGP Auto Flip settings turns early meridian settings from APCC to delayed settings. Like -2 hours to +2 hours.


thats good to know, i guess i misunderstood from the prior thread that enhancements to ascom were needed to support an early flip. maybe the enhancements to ascom are whats needed to support the “surface” of meridian limits that APCC supports, however, when ray added the “send limit to SGP” i think that’s now covered (as long as that surface is entirely beyond the real meridian.)

i suppose maybe recovery mode might be able to, well, recover from an APCC-caused meridian flip, but it might not be bulletproof.


I know @ray was working on something with controlling the limits via our API. But I’m not sure how that comes into play or how to it’s enabled on n APCC.


ray added it to APCC and it does work, but i did not test what happens if there is a meridian limit set in APCC which is before the meridian (i ended up putting my OTA on blocks to avoid having to set any meridian limits before the real meridian.)

if i understand all the moving parts right, SGP will not accept a negative meridian delay in the UI or in the API, so not sure if an error would be thrown or if SGP would just clamp to 0, or what, if there were pre-meridian meridian limits set in APCC.

I’m interested in this as well. The AP mount will flip well before or well after and we can do the flip well before on a target and never have it pause to flip during a shooting session. (starting weights up). It’s been confusing to configure. SGP or APCC? Recently I toggled off send meridian limits to SGP and trying to see if APCC can handle it and have SGP ignore it.

the problem is that SGP is not prepared for the mount to flip on its own. SGP wants to initiate the command that causes the mount to flip so that it can ensure the flip happens inbetween images.

if APCC decides to flip the mount without SGP’s knowledge, there are a few scenarios. 1) if SGP was doing nothing, waiting for the next target, it would probably work OK. 2) if SGP was in the middle of an image, the guider will fail as the mount is flipped. at that point, if recovery mode is not active, game over. if recovery mode is active, it’s possible that SGP would recover. in either case the frame in progress while the mount flipped is ruined.

Actually, I think there is an easy solution to this that doesn’t require SGP’s involvement.

You can do this in APCC’s meridian limits editor by defining your West side meridian limits to be negative (left of the meridian on APCC’s graph) to match the East side’s (yes, you CAN do that!).

Then, enable both East and West meridian limits. This works if the target you are imaging is within the East-side meridian limits when SGPro starts imaging the target. (Doing multiple targets this way might be too difficult to guarantee correct timing/position).

Anyway, APCC will force the mount to an East side counterweight up position and never flip as the scope passes the meridian and continues tracking all the way to the horizon.


makes sense - if you can prevent a meridian flip, then SGP will never get lost.

but yeah as you point out multiple targets might be too hard; for me with such a limited view of the sky i have to run 2-3 targets per night and so it’s easiest to just let SGP manage the session using pier flips.