egg changed the topic of #principia to: Logs: https://esper.irclog.whitequark.org/principia | <scott_manley> anyone that doubts the wisdom of retrograde bop needs to get the hell out | https://xkcd.com/323/ | <egg> calculating the influence of lamont on Pluto is a bit silly…
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<queqiao-> ⟨Charon_S.⟩ Hi, I have some difficulties in understanding Principia
<queqiao-> ⟨Charon_S.⟩ Can someone help me?
<queqiao-> ⟨Charon_S.⟩ I tried to modify the initial state of the solar system, but when I use the Horizons System to calculate the initial state on 1950-01-01, I occurred some problems.
<queqiao-> ⟨Al₂Me₆⟩ ⟪Charon_S.⟫ I tried to modify the initial state of […] ⮪ Why do you need to do that?
<queqiao-> ⟨Charon_S.⟩ I want to make the game start on a new date
<queqiao-> ⟨egg⟩ you don’t need to provide a new initial state for that, just set the game epoch.
<queqiao-> ⟨Al₂Me₆⟩ If that date is later than 1951 then just set the epoch, don't bother redoing states.
<queqiao-> ⟨Charon_S.⟩ ⟪egg⟫ you don’t need to provide a new initial […] ⮪ ok, I'll try. But I have few more questions
<queqiao-> ⟨Charon_S.⟩ I want to add more celestial bodies in Principia, like Saturn XXXV Daphnis. But Horizons System's time span for Daphnis is from 1990-06-14 to 2018-01-18
<queqiao-> ⟨Charon_S.⟩ so, if I do not use a new starting date, then adding Daphnis is impossible
<queqiao-> ⟨Charon_S.⟩ or, is there a way to find initial state for Daphnis on 1950-01-01? Like another website?
<queqiao-> ⟨Al₂Me₆⟩ ...considering it was discovered in 2005 that seems like a tall order.
<queqiao-> ⟨Charon_S.⟩ ⟪Al₂Me₆⟫ ...considering it was discovered in […] ⮪ I cannot figure out why just Daphnis's time span are set that way
<queqiao-> ⟨Charon_S.⟩ ridiculously, Saturn's other moons discovered after Daphnis have a time span before 1950-01-01
<queqiao-> ⟨Charon_S.⟩ that confused me a lot
<queqiao-> ⟨Charon_S.⟩ 🤔
<queqiao-> ⟨egg⟩ The Jet Propulsion Laboratory works in mysterious ways.
<queqiao-> ⟨egg⟩ I suppose then you do need a new initial state. That is somewhat annoying, because you need to give HORIZONS all the right settings.
<queqiao-> ⟨egg⟩ This is the basic query we used: https://github.com/mockingbirdnest/Principia/blob/master/astronomy/query.f
<queqiao-> ⟨egg⟩ We did it via the email interface. https://ssd.jpl.nasa.gov/horizons/
<queqiao-> ⟨egg⟩ That looks about right, but it is fiddly enough that I wouldn’t do it by hand.
<queqiao-> ⟨Charon_S.⟩ seems like it's not an easy task...
<queqiao-> ⟨egg⟩ On the other hand the email interface is weird too, and you still need to do quite a bit of automated processing to produce the initial state files.
<queqiao-> ⟨egg⟩ this thing was involved to convert them to textproto https://github.com/mockingbirdnest/Principia/blob/master/astronomy/generate_initial_state.awk, and then the Principia tools convert the textproto to the cfg we ship.
<queqiao-> ⟨egg⟩ In your case you would probably want to convert directly to cfg, without having to go through the Principia tools.
<queqiao-> ⟨Charon_S.⟩ well...I see
<queqiao-> ⟨Charon_S.⟩ a lot works to do😫
<queqiao-> ⟨Charon_S.⟩ another question:
<queqiao-> ⟨Charon_S.⟩ after changing the epoch, does RSSDateTime follow it as well?
<queqiao-> ⟨egg⟩ You need to set a corresponding configuration field in RSSDateTime.
<queqiao-> ⟨Charon_S.⟩ ⟪egg⟫ You need to set a corresponding […] ⮪ add a new cfg file?
<queqiao-> ⟨Charon_S.⟩ I failed to find any .cfgs related to that
<queqiao-> ⟨egg⟩ You should always do whatever you do in new cfg files, editing the files of other mods is brittle. If you need to edit an existing configuration you should do it as an MM patch.
<queqiao-> ⟨egg⟩ I don’t RSSTimeFormatter ships with a config though, so I suppose your cfg would have to create the node rather than edit it.
<queqiao-> ⟨Charon_S.⟩ ok
<queqiao-> ⟨egg⟩ +think
<queqiao-> ⟨Charon_S.⟩ ⟪egg⟫ That looks about right, but it is […] ⮪ I've checked, my settings should be correct, but there's a strange thing
<queqiao-> ⟨Charon_S.⟩ For example, Ariel, the default Principia setting:
<queqiao-> ⟨Charon_S.⟩ body {
<queqiao-> name = Ariel
<queqiao-> x = -1.854514651748800e+08 km
<queqiao-> y = +2.589916889179038e+09 km
<queqiao-> ⟨Charon_S.⟩ but the Horizons System's calculation result:
<queqiao-> ⟨Charon_S.⟩ 2433282.500000000 = A.D. 1950-Jan-01 00:00:00.0000 TDB
<queqiao-> X =-1.854524199015450E+08 Y = 2.589916989118511E+09 Z = 1.136815924069601E+09
<queqiao-> VX=-1.057798073099668E+01 VY= 1.111238437307262E+00 VZ=-3.841400268966394E+00
<queqiao-> ⟨Charon_S.⟩ For the x state, as you can see, there's a minute difference between -1.854514651748800e+08 and -1.854524199015450e+08
<queqiao-> ⟨Charon_S.⟩ but that's enough to make a difference on the cosmic scale
<queqiao-> ⟨Charon_S.⟩ I don't know why that happen
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