feat: port multi-satellite 2D ground tracks

[nabobalis]

Adds an optional Multi mode for future ground tracks on the 2D map.

Sel preserves the existing focused-track behavior.
Multi displays up to 8 active satellite tracks.
Additional tracks share a bounded propagation budget to limit rendering cost.
Multi-track colors follow the active theme.
Apsis markers remain limited to the focused satellite.
Slider is now discrete values.

Hopefully now up to date with the latest changes.
I think with this PR, closes #38

Thank you again for creating this program and letting me spam you with all these PRs.

[nabobalis]

Just to see it all working on the screen.

I hope to one day ditch the intel mac but thats in the future and that will make life easier.

[aweeri]

I like the feature!
No worries about the PR spam, I certainly do appreciate the perspective of someone way deeper in the field than I myself am :)

I'd love to merge this, but I'm wondering how we can make it more in-line with the style of the layers panel (this part I'll tackle myself) and more useful for the average user. The current implementation feels a bit personalized, especially given the 8-satellite limit and how it semi-randomly picks them from a larger object set.

My main issue is:

• As mentioned previously, the feature feels rather personalized given the 8 satellite limit. There already exists a system that prevents total failure with thousands of tracks drawn- more tracks just means lower per-track resolution, not a full on CPU meltdown. I think that's something that should be allowed, to make this feature more understandable for the average user, even if obviously unusable to anyone who's serious about what they're doing.

I see two ways to address this:

• we either reuse your manually defined colors over and over for all active satellite tracks.
• we implement a system that allows "secondary selections" of sorts. (This was already requested of TLEscope before, but I am unsure about the usability of it and fail to think of an actual reason to implement it in general)

[nabobalis]

Yeah, originally I was thinking of adding a color picker per satellite and then letting the user pick as many to track as thet want.

I ended up deciding to scrap that and go this approach to reduce the amount of code. It isn't really a general solution, only one basically created for my use case.

I am happy to make any changes to the feature as you want. I can't say I have any strong feelings, so I will defer you to on how best you want this actually implemented.

I will say that adding the color to the themes isn't great, some of the lines are too similar and tbh I don't think a theme or theme creator should have to worry about the track colors.

[aweeri]

I 100% agree that the use of themes is icky, but simply hardcoding the colors or writing a little dynamic color assigner of sorts would take power away from the user when it comes to theming so it's a bit of a lose-lose situation :/
I think I'll merge it and I'll ponder how I can clean up the backend and the UX around it, as this feature has revealed quite a few issues with how things are implemented in general :P

[nabobalis]

The UX in Xephlem is roughly this. You have to first favorite the satellites you want. Then in a separate window, you get a table of all the favorites, an option to hide or show the location, then to hide or show the track, some toggle buttons about other properties and then a separate pop up if you want to change color of the tracks or other properties of the track. I can't say I liked it.

[aweeri]

powerful, but sounds like a mouse clicking nightmare. It gave me an idea however!

I could probably add some sort of simpler implementation of a "favourites" system;
you would be able to star objects in the satellites manager itself, and all it would do would be:

• force labels on all favorited satellites (on second thought, this is managed by layer dropdowns too.)
• dropdowns next to relevant layer toggles could have "Fav" in addition to "Sel" and "All"
• more,(likely obvious) stuff that my brain isnt thinking of right now