Re: [Orekit Users] transformation

[MAISONOBE Luc <luc.maisonobe@c-s.fr>]

Hi Martin,

Martin <martin.spel@rtech.fr> a écrit :

> I am looking at how to transform an initial condition defined by (longitude,
> latitude, altitude, relative velocity, flight path angle and orbit  
> inclination
> angle), to orbital parameters that can be used by Orekit. Is somebody already
> using such transformation or can has some reference on a transformation that
> can be used?

You can use a trick to achieve this result: use a TopocentricFrame.

First, set up the frame using the latitude, longitude and altitude  
(using an intermediate GeodeticPoint object). You can build the  
relative velocity from velocity amplitude and spherical angles flight  
path and inclination in this frame, knowing that its X axis is towards  
East, and Z axis towards zenith. In this frame, your spacecraft  
coordinates are (0, 0, 0) for position and (vx, vy, vz) for velocity.  
You just have to transform it to any other frame like EME2000 using  
the standard frame transforms. Here is a rough skeleton of this process:

  GeodeticPoint gp = new GeodeticPoint(latitude, longitude, altitude);
  TopocentricFrame frame = new TopocentricFrame(earth, point, "initial");
  Vector3D relativeV = new Vector3D(....);
  Transform t = frame.getTransformTo(FramesFactory.getEME2000(), date);
  PVCoordinates pv2000 =
    t.transform(new PVCoordinates(Vector3D.ZERO, relativeV));

best regards,
Luc

>



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