00:17 <queqiao-> ⟨Starscraper⟩ So, when you do an orbit analysis in Principia, what is the

00:17 <queqiao-> "longitude of the ascending node" in reference to? I know what LAN is, just not what it's being measured with respect to, since it seems like it can't be geographic longitude since it's not changing with the Earth's spin. Is there some reference celestial sphere longitude or something?

00:18 <queqiao-> ⟨lpg⟩ the first point of aries

00:18 <queqiao-> ⟨lpg⟩ (don't ask me what that means, but do ask google if you don't already know)

00:20 <queqiao-> ⟨lpg⟩ it is noteworthy that stock ksp's LAN does _not_ use the first point of aries

00:20 <queqiao-> ⟨Starscraper⟩ Ah, so it is on the celestial sphere - more importantly, it's inertial. That's nice, thanks.

00:20 <queqiao-> ⟨lpg⟩ (and so mechjeb (for example) and principia don't agree. I think it's a fixed offset, but don't recall what)

00:21 <queqiao-> ⟨Starscraper⟩ Now to find out how it relates to KSP's internal base coordinate system...

00:22 <queqiao-> ⟨lamont⟩ i don't quite understand that, why is stock KSP's Planetarium.right not the first point of ares?

00:24 <queqiao-> ⟨Starscraper⟩ Now to find out how it relates to KSP's […] ⮪ If anyone knows off the top of their head that'd be really cool, but it's a rather obscure question so I'm gonna go hunting for that through a little experimenting.

00:24 <queqiao-> Need it so I can write a kOS ascent program that can launch into an orbit of a given inclination and LAN (or at least, tell how far off the current launch site currently is from being on the target orbital plane)

00:24 <queqiao-> ⟨lamont⟩ and is the discrepancy with Principia and MJ more to do with RSS using the wrong orbital elements?

00:25 <queqiao-> ⟨lamont⟩ i'm probably missing something simple

00:25 <queqiao-> ⟨lpg⟩ I'll just clarify that when I said "stock ksp", I meant "principia-less RSS". I have no further information on the topic

00:26 <queqiao-> ⟨lamont⟩ lol, makes sense

00:27 <queqiao-> ⟨lpg⟩ Really, the extent of my knowledge is that if I get a LAN out of TWP and feed it into PVG, I get the expected results; but then principia displays a different LAN. And previous discussions have convinced me that principia isn't the one doing it wrong

00:28 <queqiao-> ⟨lpg⟩ * "wrong"

00:37 <queqiao-> ⟨lamont⟩ yeah that seems at least awkward, and I'm trying to sort out if MJ should do something different. it kind of sounds like RSS needs to get fixed (but that smells like a hard breaking change that would ruin saves, unless you wrote some kind of migration tooling)

01:00 <queqiao-> ⟨Quadrupole⟩ ⟪lpg⟫ (and so mechjeb (for example) and […] ⮪ MJ and stock's LAN is greater than Principia's LAN by exactly 270 degrees

01:00 <queqiao-> ⟨Quadrupole⟩ * are

01:00 <queqiao-> ⟨Quadrupole⟩ +(and the correct one)

01:01 <queqiao-> ⟨Quadrupole⟩ * (the

01:04 <queqiao-> ⟨Quadrupole⟩ So for example, MJ and stock would tell you the moon's LAN (wrt earth's equator) is around 270 degrees, whereas Principia and other ephemerides would tell you it's actually around 0 degrees.

03:05 <queqiao-> ⟨lpg⟩ I'll go on a limb and say no MJ _by itself_ shouldn't do something different. TWP and MJ agreeing is a fairly useful property

03:22 <queqiao-> ⟨Starscraper⟩ Well, I've been experimenting around to see if I could find the formula for getting the orbit normal vector in game coordinates from Principia's Inclination and and LAN values.

03:22 <queqiao-> Using kOS "print vcrs(body:position, ship:velocity:orbit):normalized" to get the orbit normal vector. Or, anti-normal, as the case may be. I dunno of the left-handed coordinate system flips it or not with kOS's cross product - but whatever, the important thing is it's orthogonal to the orbital plane.

03:22 <queqiao-> And I seem to have gotten the formula. But there seems to be a small correction factor "L0" for the formula, which is kinda odd.

03:22 <queqiao-> x = -sin(LAN + L0) * sin(Inc)

03:22 <queqiao-> ... long message truncated: https://matrix.mockingbirdnest.com/_matrix/media/r0/download/matrix.mockingbirdnest.com/HEBFKhzqnNETpGrvPoauavBL (8 lines)

06:54 <kitty> 🐈 hows it going?

07:47 <kitty> raptop: how have you been?

07:48 <raptop> surviving, not as much progress as I'd like on things, but *gestures vaguely*

09:19 <kitty> raptop: valid, thats a mood~ 🐈

12:53 <queqiao-> ⟨egg⟩ ⟪Starscraper⟫ So, when you do an orbit analysis in […] ⮪ This comment may have some answers for you. https://github.com/mockingbirdnest/Principia/blob/7e8200a620b19e29455c2df5baccbc5888cdd52b/physics/body_centred_non_rotating_dynamic_frame.hpp#L34-L53

13:27 <queqiao-> ⟨Butcher⟩ Raptop, TI-92 is 68000 so it's kinda 16-bit

19:15 <queqiao-> ⟨Starscraper⟩ ⟪egg⟫ This comment may have some answers for […] ⮪ Are these the coordinates used to derive the Inclination and LAN that Principia displays?

20:14 <queqiao-> ⟨egg⟩ Yes.