Question Global position in Orbiter

Ajaja

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API_Reference.pdf:
oapiGetGlobalPos() Returns the position of an object in the global reference frame.
"The global reference frame is the heliocentric ecliptic system at ecliptic and equinox of J2000."

Heliocentric? But Sun at J2000 (MJD 51544.5) is not in (0,0,0) if oapiGetGlobalPos() does not lie.
Solar System Barycenter? But planets positions in comparsion with data from JPL's HORIZONS system http://ssd.jpl.nasa.gov/horizons.cgi have big error (about ~100km for Mars with ErrorLimit=1-e8, for example). It's too big error for VSOP87.

Where is (0,0,0) in Orbiter?
 

Hielor

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API_Reference.pdf:
oapiGetGlobalPos() Returns the position of an object in the global reference frame.
"The global reference frame is the heliocentric ecliptic system at ecliptic and equinox of J2000."

Heliocentric? But Sun at J2000 (MJD 51544.5) is not in (0,0,0) if oapiGetGlobalPos() do not lie.
Solar System Barycenter? But planets positions in comparsion with data from JPL's HORIZONS system http://ssd.jpl.nasa.gov/horizons.cgi have big error (about ~100km for Mars with ErrorLimit=1-e8, for example). It's too big error for VSOP87.

Where is (0,0,0) in Orbiter?
Fairly sure (0,0,0) is the center of the sun, with the other axes defined according to J2000?
 

Ajaja

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Fairly sure (0,0,0) is the center of the sun, with the other axes defined according to J2000?

I use small MFD for test:
Code:
void MFDTemplate::Update (HDC hDC)
{
	Title (hDC, "MY MFD");
	OBJHANDLE h1 = oapiGetObjectByName("Sun");
	char buffer[60];
	VECTOR3 p1,v1;
	oapiGetGlobalPos(h1,&p1);
	oapiGetGlobalVel(h1,&v1);
	int length=sprintf(buffer,"%.2f %.2f %.2f", p1.x, p1.y, p1.z);
	TextOut(hDC,2,40,buffer,length);
	length=sprintf(buffer,"%.2f %.2f %.2f", v1.x, v1.y, v1.z);
	TextOut(hDC,2,100,buffer,length);
}
For MJD 51544.5 (J2000) with ErrorLimit=1e-8 in Sun.cfg Sun position:
x=-1068357201.07 m
y=30838190.43 m
z=-417104486.53 m

It's close to SSB (from HORIZONS):
Code:
*******************************************************************************
Target body name: Sun (10)                        {source: DE405}
Center body name: Solar System Barycenter (0)     {source: DE405}
Center-site name: BODY CENTER
*******************************************************************************
Start time      : A.D. 2000-Jan-01 12:00:00.0000 CT 
Stop  time      : A.D. 2000-Jan-01 12:01:00.0000 CT 
Step-size       : 60 steps
*******************************************************************************
Center geodetic : .000000000,.000000000,.00000000 {E-lon(deg),Lat(deg),Alt(km)}
Center cylindric: .000000000,.000000000,.00000000 {E-lon(deg),Dxy(km),Dz(km)}
Center radii    : (undefined)                                                  
Output units    : KM-S                                                         
Output format   : 02
Reference frame : ICRF/J2000.0                                                 
Output type     : GEOMETRIC cartesian states
Coordinate systm: Ecliptic and Mean Equinox of Reference Epoch                 
*******************************************************************************
JDCT 
   X     Y     Z
   VX    VY    VZ
*******************************************************************************
$$SOE
2451545.000000000 = A.D. 2000-Jan-01 12:00:00.0000 (CT)
  -1.067599061683767E+06 -4.182344023414851E+05  3.083742139134574E+04
   9.312571755237429E-03 -1.282475173644486E-02 -1.633340301099347E-04

But difference about ~1360 km . It's too big. Maybe SSB is(0,0,0) but something wrong with VSOP87 in Orbiter?
 
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