Meridian Flip not working north of pole

[leafar-izen]

I submitted this bug to Jasem in Ekos, he says it's rather for you guys....

SUMMARY
Although MF works fine when crossing meridian south of NP, it does not happen when crossing meridian in between North horizon and NP ( i guess the problem would be the same in south hemisphere, crossing meridian somewhere between SP and South Horizon.)

Set Up : Using a OnStep mount.
Note : when I try the same experiment with a Mount Simulator, the simulated mount does perform the flip correctly. Is it a bug specific to OnStep Mount and it's parameters ? Or would it occur in any real mount ? I don't know.

In INDI control panel, OnStep mount is configured like this : Autoflip : OFF (defaut); Preferred Pier side : EAST (tested with WEST also, same problem); Minutes past meridian E/W: 10/10.
Those settings works fine for Meridian Flip (MF) south of north pole (NP), up to south horizon.

STEPS TO REPRODUCE

1. Start Kstars/Ekos and connect your devices.
2. setup MF in Ekos mount tab ( exemple: MF if HA>0 degre)
3. Point to an object that is north, below NP and close to meridian, in west hemisphere (in this area meridian is crossed from west to east)
4. Wait for countdown until MF to reach zero.

OBSERVED RESULT

First, before even reaching time for MF, we can highlight two little inconsistencies in INDI Gui (and Ekos) :
1 - It says "Pier Side : East (pointing West). But actually, the pier is WEST. (In this specific region of the sky, mount pier is West to point West and East to point East...)

2 - for this area, it's not "Flip if HA>x degre", It should rather be "Flip if HA > 12 hours - 4x
(Like if you set Flip if HA>1 degree. In this north section of meridian, you want "Flip if HA > 11h 56m 00s"
But I notice that when i put 1 degree, count down target 4 minutes east of meridian ( HA = -11h 56m 00s).
It seems to try MF at HA = -12h 00m 00s + 4x = -11h 56m 00s ( for x=1 degree). But as we come from WEST instead of EAST, reversing the sign may fix the problem : So that condition become "Flip at HA > 12h 00 00 - 4X" )

Then, when count comes to zero, console says "Meridian flip running"..., but nothing happen, and the mount get stuck with tracking stopped.

EXPECTED RESULT

1 When mount is tracking an object in western hemisphere and crosses the "east/west meridian", (ie: line going through poles and west and east horizon) : the Pier Side should change to West (Pointing west)

2 When reach the meridian, mount should perform a proper MF and track circumpolar object in east hemisphere (with Pier on East (Poiting East)

SOFTWARE/OS VERSIONS
Windows:
macOS: Big Sur
(available in the Info Center app, or by running kinfo in a terminal window)
Linux/KDE Plasma:
KDE Plasma Version:
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.13

ADDITIONAL INFORMATION

• The same issue arized in NIMA years ago and is discussed here:
  https://www.cloudynights.com/topic/746613-nina-meridian-flips-fail-north-of-polaris/
  Seems they have fixed it since then.

Good skies

[knro]

@azwing It would be great if you can take a look at this.