Transforming geodetic points to spacecraft body frame

Orekit Python Wrapper usage
2

Hello @saltinisik,

What you’re trying to achieve looks very much like what @Echulion already asked for at the end of this thread.
Am I right @Echulion ?

I will try to answer, hoping that I can help the both of you.

Suppose you have a SpacecraftState state and a GeodeticPoint geoPoint.

// Get the reference frame of the SpacecraftState (the inertial frame where the orbit is computed)
Frame refFrame = state.getFrame();

// Get the position of the SpacecraftState in ref frame
Vector3D satPosInRefFrame = state.getPVCoordinates().getPosition();

// Get its date
AbsoluteDate date = state.getDate();

// Get the attitude of the spacecraft (a rotation from reference frame to "satellite" frame)
Attitude attitude = state.getAttitude();

// Get the underlying topocentric frame of the geodetic point
TopocentricFrame topoFrame = new TopocentricFrame(earth, geoPoint, "topoFrame");

// Get the geodetic point position in reference frame
Vector3D geoPointInRefFrame = topoFrame.getPVCoordinates(date, refFrame).getPosition();

// Let O be the center of frame, S the satellite and P the geodetic point
// Compute satellite to geodetic point vector: SP = - OS + OP
Vector3D sat2GeoPoint = geoPointInRefFrame.subtract(satPosInRefFrame);

// Normalize the vector and rotate it using the attitude
Vector3D geoPointDirectionInSatFrame = attitude.getRotation().applyTo(sat2GeoPoint.normalize());

With this you should have the geodetic point direction in satellite frame (i.e. a unit vector pointing to the geodetic point with respect to the satellite position and attitude).

Is that what you are looking for ?

Maxime

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