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[Orekit Users] Reference frame of a S/Cs attitude

Dear list members,

I'm in the course of developing a simple application using Orekit to 
calculate the time series of the following paramters for a satellite link 
to an earth ground station:

1. slant range
2. elevation (as seen from G/S)
3. S/C-G/S-Sun angle
4. two offset angles between an antenna on the S/C and the line of sight 
to the G/S.

Currently I am able to produce parameters 1 and 2 using the following 

SpacecraftState currentState = propagator.propagate(now);
PVCoordinates topoScPv = currentState.getPVCoordinates(gsTopoFrame); // 
gsTopoFrame is the topocentric frame of the G/S on earth

double slantRange = gsTopoFrame.getRange(topoScPv.getPosition(), 
gsTopoFrame, now);
double elevation = gsTopoFrame.getElevation(topoScPv.getPosition(), 
gsTopoFrame, now);

Is this the correct approach?

Could anyone please give me a hint at how to get the S/C->G/S unit-vector 
in the frame of reference of the S/C with it's attitude applied (parameter 
4)? I would like to use this vector to extract two angles relative to an 
antenna in order to evaluate the antenna gain in direction of the G/S. My 
basic problem is that I don't really know how I can get the S/C-bound 
Frame that is oriented according to the attitude of the S/C. The only 
S/C-bound frames I can produce are TNW, VNC, QSW/VLVH and VVLH which are 
all not related to attitudes.

In order to get the S/C-G/S-Sun angle (parameter 3), I guess it would be 
enough to get the unit vectors a = G/S->S/C and b = G/S->Sun in a common 
reference frame (e.g. the G/Ss topocentric frame) and then set the angle 
to be equal acos(a.normalize().dotProduct(b.normalize())). Is that 

Many thanks for your time and effort for producing this very handy 
Best regards,

Raffael Mancini

PS: Have you ever considered introducing a type that would somehow couple 
vectors with frames? This could make it possible either at compile or 
runtime to check if the vectors are in the same frame.

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