Newcomer / Intro Planetary Longitudes

[Dog Zebra USN]

Looking at some of Scott Manley's YouTube videos, he talks about how -- essentially -- the prime meridians on local planets like Venus and Mars (and Earth) are set somewhat arbitrarily. Greenwich was set as the Prime Meridien here on Earth; on Mars, the landing site of Viking 1 sets a reference longitude which they use to establish the prime.

In ED, what logic's being used to set the longitudinal lines? And is it 'pre-ordained' (set before any CMDR has entered the system) or is it set when the first CMDR enters?

Lol, it's driving me nuts trying to figure out what FDev's approach is!

And just for completeness' sake, latitudinal lines are IMHO pretty easy -- once you assess the rotational axis and circumference, you've got your lines of latitude. But longitude -- that's a different story... or is it?

Thanks!

 

[Chris Simon]

I think it is determined simply from the planet's 3D model in the code. Every model has X, Y, Z coordinates in the code, that means it automatically has six "poles" where the axes intersect with the surface. All planets have "Y" axis ( the "North") facing the same direction (AFAIK). So based on that and the fact that the in-game coordinates count from -180° to 180° instead of 0-360 I think they simply coded one of the equatorial poles' (X or Z) positive end intersection to define zero meridian and carried on from there.

Or it's black magic. Also a possibility with a lot of Elite's nebulous inner workings.

 

[Dog Zebra USN]

Hi, Chris -- thanks for the reply, and I bet you may be right -- they had to use some approach to establish the prime, and like you said, they've got one from the 3D model.

By the way, I came across this link: IAU Working Group on Cartographic Coordinates and Rotational Elements -- they're the guys trying to solve the problem IRL. I wouldn't blame FDev one bit for basing it off the model, but I also wouldn't be surprised if there's a software engineer in a cube somewhere, trying to figure out how to resolve the Galactic Core as the reference point for all of their planets!

 

[Evil Horse]

I have the same question -- trying to write a custom plugin for EDDiscovery showing other bodies' elevation above (or below) horizon for given CMDR position (and, in future, altitude)

 

[Alec Turner]

Subscribing to this thread. As a serial planetary circumnavigator I'm definitely interested in this stuff. I'm guessing the position of longitude zero is a value which simply pops out, perhaps somewhat arbitrarily, from the procgen. Given planets are all constantly rotating to varying degrees in real time, where each planet's longitude zero started at back at some nominal time zero is sort of irrelevant isn't it?