[kstars] [Bug 496975] New: Meridian Flip not working north of North Pole

[Leafar Izen]

https://bugs.kde.org/show_bug.cgi?id=496975

            Bug ID: 496975
           Summary: Meridian Flip not working north of North Pole
    Classification: Applications
           Product: kstars
           Version: 3.7.2
          Platform: macOS (DMG)
                OS: macOS
            Status: REPORTED
          Severity: minor
          Priority: NOR
         Component: general
          Assignee: mutlaqja at ikarustech.com
          Reporter: leafar.izen at gmail.com
  Target Milestone: ---

SUMMARY
Set Up : Using a OnStep mount 
In INDI control panel, 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).

Although MF works fine when crossing meridian south of NP, it does not happen
when crossing meridian in between North horizon and NP.

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 highligh two little
inconsistencies in Ekos Guide Tab:
1 - It says "Pier Side : East (pointing West). But actually, 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 seem 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.

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


EXPECTED RESULT
Perform MF and track circumpolar object in east hemisphere.

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.

- It is not critical at all for me. I don't even see this sky zone from my
BY... ;-) Just trying to help to improve this great piece of software. Maybe it
is more a burden for people living north of Finland...

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