DCS and matrix help needed please.

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Daniel Delgado (renata++at++eos.arc.nasa.gov)
Thu, 1 Aug 1996 13:03:07 -0700


Subject: DCS and matrix help please

Hi all ...
     
    How does one convert a point in a DCS coordinate system to the original coordinate
system after translating and rotating the DCS one?

What I mean is that I did this with a DCS

   /* update vehicle DCS */

            pfDCSRot(vehicle[0].dcs,
                 vehicle[0].hpr[PF_H],
                 vehicle[0].hpr[PF_P],
                 vehicle[0].hpr[PF_R]);

            pfDCSTrans(vehicle[k].dcs,
                   vehicle[0].xyz[PF_X],
                   vehicle[0].xyz[PF_Y],
                   vehicle[0].hpr[PF_Z]);

Now I have a point that is in the original Performer Coordinate system (vehicle[1].xyz)
and I want to find out what its value is in the rotated and translated DCS system.

I think I know just enough to screw up! In other words, the approach below is
Wrong wrong wrong....

    pfGetDCSMat(vehicle[0].dcs,Matrix1);
    pfXformPt3(IntrusionVect, vehicle[1].xyz, Matrix1);

     xnew = IntrusionVect[PF_X] + (vehicle[1].xyz[PF_X] - vehicle[0].xyz[PF_X]);
     ynew = IntrusionVect[PF_Y] + (vehicle[1].xyz[PF_Y] - vehicle[0].xyz[PF_Y]);
     znew = IntrusionVect[PF_Z] + (vehicle[1].xyz[PF_Z] - vehicle[0].xyz[PF_Z]);
  
xnew and ynew and znew are way off!

Any advice? What am I doing wrong? Any
help would be much appreciated!

Daniel Delgado
delgado++at++elmo.arc.nasa.gov
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