Add abort telescope slew signals to LX200 and NexStar telescopes

[gzotti]

Description

I found that most telescopes are missing the AbortSlew implementation. This is severely bad. This PR should add the signals at least for LX200 and NexStar.

However, I cannot test it, so this needs external help. I unassigned myself for now in the hope one of our active observers steps in. It may just take a rainy weekend or two. Of course, support for a Big Red Button (emergency switch, separate hardware) would also be nice!

Fixes # (issue)

• Add AbortSlew to LX200
• Add AbortSlew to NexStar
• Add graceful recovery (put back marker) to LX200
• Add graceful recovery (put back marker) to NexStar

Screenshots (if appropriate):

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• This change requires a documentation update

How Has This Been Tested?

Test Configuration:

• Operating system: Windows 10 or any other
• Graphics Card: irrelevant

• Tested AbortSlew for LX200
• Tested AbortSlew for NexStar

Checklist:

• My code follows the code style of this project.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (header file)
• I have updated the respective chapter in the Stellarium User Guide
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[alex-w]

You should read the target coordinates from the mount after stopping slewing and place marker in these coordinates

[gzotti]

You should read the target coordinates from the mount after stopping slewing and place marker in these coordinates

If I knew how this positioning interpolation stuff works I could maybe do that. But while I can estimate that I should test with hasKnownPosition() and can likely retrieve pos with getJ2000EquatorialPos(), I know zilch how to set that. How do the InterpolatedPositions work? Is that a ring buffer? What is the purpose of Position.{server_micros, client_micros,status}? Dev docs are so annoyingly often missing or useless in this plugin! IDC where some struct had been defined 15 years ago and "now" moved over. I wish somebody could reverse-engineer a design document for this plugin!

[alex-w]

InterpolatedPositions is own implementation of interpolation and this is does not touches NexStar/LX200 implementation - it's similar, not equal. LX200/NexStar protocols have methods for getting current coordinates from the mount and this parts of protocols are not implemented.

[alex-w]

The Telescope Control plugin should be fully redesigned and rewritten and it should support asynchronous for connection to the devices. I full agree - we need experts for it.

[gzotti]

I see that the TelescopeClientDirectLx200 has an interpolatedPosition that does something. But I don't dare touching this without fitting device and high enough personal interest in this plugin. Anyone out there?

[A-j-K]

The Telescope Control plugin should be fully redesigned and rewritten and it should support asynchronous for connection to the devices. I full agree - we need experts for it.

It's not async by design? Oh! Hmm, if I'm diving into this plugin then, as others said, it may need a rethink. And then I'd need to find folk with hardware who can test. I have a SkyWatcher mount but that's it, not the others.