API Question What's the origin of Coordinate System in Orbiter?

[Evgheny]

Hello Forum.

What is the origin of Coordinate System in Orbiter?

I use this function from Orbiter SDK API:

oapiGetGlobalPos
Returns the position of an object in the global reference frame.
Notes:
• The global reference frame is the heliocentric ecliptic system at ecliptic and
equinox of J2000.
• Units are meters.

I've got position of Sun and Earth by this function: (values are rounded to integers)

Sun:
[ -604130529 21220719 -773332607]
Earth:
[ -148621181901 20988065 14095190016 ]

R = dist(sunPos, earthPos) returns 148761959054, that's similar to 149.6*10^6 from wikipedia.

But what's the center of this coordinate system?

I've found this picture (below) on wikipedia on page for ecliptic system:

So, Sun should be approximately [0 0 0] and Earth should be [x y 0] where sqrt(x^2+y^2) = R (distance from Sun to Earth)

But in our case I see that coordinate y is similar, but not z. And Sun is not in the center of system coordinate.


I think, I don't really understand this ecliptic frame - may be it's related to mjd value?

 

[Urwumpe]

You have to understand, that the coordinate system is left handed, because it was designed for DirectX, which is also left handed. The center is the barycenter of the solar system, not the sun. also, y is in orbiter, what your z in the wikipedia diagram is.

 

[Evgheny]

Thank you, now I understand.

 

[statickid]

i noticed minecraft has a similar definition of y. is there a specific reason that orbiter and minecraft use y as a "vertical"?

 

[Loru]

is there a specific reason that orbiter and minecraft use y as a "vertical"?

dunno about minecraft but Orbiter, as Urwumpe said it uses same system as directX. I'm not a coder but that's logical to me. Graphical client uses same coordinate system as physics engine and there is no need to translate position data. That's how you save computing power

 

[sorindafabico]

Where is (0,0,0)?

 

[Urwumpe]

Where is (0,0,0)?

At the barycenter of the solar system. This is approximately the center of mass of the solar system (With some extra definitions for accuracy)

 

[Evgheny]

Coordinates Y of Sun and Earth are not equal. It means that Orbiter XZ Plane (Y=0) is not parallel to Ecliptic Plane? Why does it call Ecliptic Frame then?

 

[Hielor]

Google is your friend: [ame="http://en.wikipedia.org/wiki/Ecliptic"]Ecliptic - Wikipedia, the free encyclopedia[/ame]