01:23 <discord-_> e​gg. — OK I updated https://github.com/Kerbalism/Kerbalism/wiki/Dev-~-Satellite-Contracts#systems-based-on-timing-and-ranging with some PDOP/pseudorange blather and added a section on TRANSIT https://github.com/Kerbalism/Kerbalism/wiki/Dev-~-Satellite-Contracts#transit

01:24 <discord-_> e​gg. — @bofh453 do you have any thoughts generating reasonable pseudorange errors

01:24 <discord-_> e​gg. — (see first link in my preceding post)

02:09 <discord-_> b​ofh453. — @egg: I've looked at it awhile back and I'm actually still not sure. DOP/pseudoranges are kind of a mess in how one and the other interact tbh.

02:10 <discord-_> e​gg. — @bofh453 eh, DOP is a bit of a hack, but I think assuming uncorrelated pseudorange errors you can directly work with (8) of https://gssc.esa.int/navipedia/index.php/Parameters_adjustment

02:11 <discord-_> e​gg. — (R then being diagonal and holding the pseudorange variances, and the vertical and horizontal errors being the traces of the relevant submatrices of P in a NED (or ENU) frame)

02:12 <discord-_> e​gg. — @bofh453 my remaining question is more what contributes to pseudorange errors

02:12 <discord-_> e​gg. — and what techniques cancel what contributions

02:12 <discord-_> b​ofh453. — Hrm.

02:13 <discord-_> b​ofh453. — I'm actually not even sure what the heck techniques *would* lead to cancellation, you mean what approximations would not include certain errors, or?

02:38 <discord-_> e​gg. — @bofh453 I mean that Wide-Area Differential SBAS will reduce some effects, dual-frequency receivers get rid of the error induced by the ionosphere, etc.

02:39 <discord-_> e​gg. — @bofh453 but I don't know how to list the sources of error to estimate them for the porpoises of the game

02:39 <discord-_> e​gg. — there's error on the timing which you fundamentally cannot get rid of, but which should be tiny; then you have ionospheric effects, then you have tropospheric effects (are those mitigated by DGPS/SBAS?), what else is there?

02:50 <discord-_> b​ofh453. — Ahh, right. I would assume tropospheric effects would be mitigated by DGPS just as it mitigates building / urban island effects (iirc that's a lot of what Japan has a DGPS constellation for, for instance).

02:51 <discord-_> b​ofh453. — ionospheric effects provide the bulk of error and it turns out that you just need the phase estimate from the other frequency to correct for it, decoding isn't even necessary (see John Deere for the implementation details, YES SERIOUSLY THE TRACTOR COMPANY).

02:54 <discord-_> e​gg. — yes I know John Deere operates an SBAS

02:54 <discord-_> e​gg. — 🚜🛰️

03:03 <discord-_> e​gg. — @bofh453 wait what, DGPS mitigates urban effects? how so? reflections off buildings are super local, you're not going to have a ground station every 10 m

03:03 <discord-_> e​gg. — Japan has QZSS to mitigate urban canyons, but afaict that's just "more satellites in view", not differential?

03:07 <discord-_> e​gg. — ah QZSS does broadcast L1-SAIF which is wide-area DGPS, but being wide area that can't do much about multipath, can it?

03:10 <discord-_> e​gg. — aha there's a list in https://gssc.esa.int/navipedia/index.php/Best_Linear_Unbiased_Minimum-Variance_Estimator_(BLUE)

03:10 <discord-_> e​gg. — > where σ2yi comes from the uncertainty of the different error sources (satellite clocks, ephemeris, ionosphere, troposphere, multipath and receiver noise):

03:18 <discord-_> e​gg. — apparently you can mitigate multipath with dual-frequency too? https://www.dlr.de/kn/en/desktopdefault.aspx/tabid-4310/9657_read-23935/

03:18 <discord-_> e​gg. — > The key research tasks include

03:18 <discord-_> e​gg. — okay not yet,

06:07 <discord-_> S​ir Mortimer. — Wait. There’s a tractor in orbit?

06:09 <discord-_> A​mpersand. — there's at least one car :V

07:50 <discord-_> S​ir Mortimer. — in solar orbit, yes 🙂

11:02 <discord-_> e​gg. — @Sir Mortimer nah, but you have tractors guided by a layer on top of GPS which is operated by the tractor company

11:03 <discord-_> e​gg. — OK, some orders of magnitude from a WAAS document:

11:03 <discord-_> e​gg. — > The assumptions are as follows: signal-in-space pseudorange error of 6m; avionics pseudorange error of no more than 5m (rms); a 0.45m (rms) multipath error; a 7 m (rms) ionospheric delay model error; and, a 0.25m (rms) residual tropospheric delay error. The dominant pseudo-range error for users of the GPS Standard Positioning Service is the ionospheric error that remains after application of the io

12:02 <discord-_> B​utcher. — @egg Difference between extended-body and n-body gravity?

12:05 <UmbralRaptop> butcher: eggstended-body as in spherical harmonics for a single body

12:12 <UmbralRaptop> hence necessary for молния orbits or masscon shenanigans, but not Lagrange points

12:12 <discord-_> B​utcher. — Right, I thought it might be that.

12:42 <discord-_> e​gg. — yeah as UmbralRaptop says, n-body = multiple point (or spherically symmetric) masses pulling on you, eggstended-body = they're not points (nor spherically symmetric), they're misshapen blobs that don't quite have the same pull in all directions

12:45 <UmbralRaptop> note to self: \oplus means 🜨

13:16 <discord-_> B​utcher. — Does principia do extended-body for all celestials?

13:49 <discord-_> e​gg. — In RSS most I think

13:49 <discord-_> e​gg. — Note to self, https://gssc.esa.int/navipedia/index.php/GNSS_Measurements_Modelling

14:48 <discord-_> e​gg. — @Butcher actually you can check for yourself by looking at https://github.com/mockingbirdnest/Principia/blob/master/astronomy/sol_gravity_model.proto.txt

14:49 <discord-_> e​gg. — anything that has a `j2` or a `geopotential` has extended-body gravity in some way

14:51 <discord-_> e​gg. — (that has the moon to degree and order 50 for testing, but we only go to degree and order 30 in game)

14:52 <discord-_> B​utcher. — I did think that was a lot of data for the Moon.

14:54 <discord-_> e​gg. — 30 is still quite a lot

14:54 <discord-_> e​gg. — See https://github.com/mockingbirdnest/Principia/blob/master/astronomy/sol_gravity_model.cfg for the in-game data (but there are no comments in that one)

20:47 <discord-_> b​ofh453. — > apparently you can mitigate multipath with dual-frequency too?

20:48 <discord-_> b​ofh453. — yeah, in theory you can do so, I've successfully pulled it off using dual-frequency FDMA trunked radio receivers, the same technique *should* work for GPS.

20:48 <discord-_> b​ofh453. — I really should try to SDR a GPS receiver since picking up both frequencies is doable on an SDR tunable to either and then you can do some pretty fun DSP down the chain.

23:30 <_whitenotifier-d13c> [Principia] pleroy commented on issue #2400: History persistence lets .sfs files get very large - https://git.io/JvGqv