To test the visibility of an object in a scene, the code for a testing 
screen below has been provided by Gilles Tran. This code is for the POV-Ray 
(left-handed) coodinate system (y = up). I would like to use this for a 
(right-handed) scene built in Moray (z = up), but don't know how to rewrite 
the code for the screen. All help will be kindly acknowledged :-)

//--start code--
#declare CamLoc = <0, .3, 0>;
#declare CamEye = <0.0, 6,  0.0>;
#declare CamSky = y;
#declare AspectRatio = 640/1000;
#declare CamZoom = 1.5;

camera {
  location  CamLoc
  direction z*CamZoom
  right     x*AspectRatio
  look_at   CamEye
}

// --------------------------------------
// visibility test code by Gilles Tran,
// derived from work by
// John Van Sickle and Christoph Hormann
// --------------------------------------
#declare CamD=vnormalize(CamEye-CamLoc);         // direction of camera view
#declare CamR=vnormalize(vcross(CamSky,CamD));   // to the right
#declare CamU=vnormalize(vcross(CamD,CamR));     // camera up

#declare Screen= // pseudo screen to test the visibility of an object
mesh{
  triangle{0,x,x+y}
  triangle{0,y,x+y}
  translate -0.5*(x+y)
  scale <AspectRatio,1,1>
  translate CamZoom*z
  matrix < CamR.x,  CamR.y,  CamR.z,
           CamU.x,  CamU.y,  CamU.z,
           CamD.x,  CamD.y,  CamD.z,
           CamLoc.x,CamLoc.y,CamLoc.z >
}
//object{Screen pigment{rgbf<1,0,0,0.9>}}
//--end code--

-- 
All the best,

Thomas

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