[Plib-devel] Bug with sign of pitch?

[Wolfram K. <w_...@rz...>]

I have a trivial question:

If I am in a slightly ascending aeroplane, is my pitch positive?
I would guess so, but looking at

void sgHPRfromVec3 ( sgVec3 hpr, const sgVec3 src )

at the line

  hpr[1] = -(SGfloat) atan2 ( tmp [ 2 ], sqrt ( sgSquare ( tmp [ 0 ] )
+ sgSquare ( tmp [ 1 ] ) ) ) *
SG_RADIANS_TO_DEGREES ;

it seems to be negative, is that correct?

Here is the reason for my question:
While sg contains a function to convert a cartesian Vec3 into a HPR,
the other conversion was missing and I implemented it for PPE by
copying code from sgMakeCoordMat4. It seems to work in PPE,
but when I converted the result back as a check, I get inverted pitch.
Is the bug in my new function or in plib, for example sgHPRfromVec3 ?

BTW, I game developers might use this code as well.
I use it for camera-movement (when I do a "make object fully
visible").
Its quite simple, but perhaps you want to put it into plib?

Here is the function:

--------------------- cut ------------------------------
void /*sg*/Vec3fromHPR ( sgVec3 vec3, const sgVec3 hpr ) 
// If hpr are the hpr of the camera, then this function gives the
normalised
// viewing direction. Of course roll is lost in this conversion.
{
  double ch, sh, cp, sp; 

  if ( hpr[0] == SG_ZERO )
  {
    ch = SGD_ONE ;
    sh = SGD_ZERO ;
  }
  else
  {
    sh = (SGfloat) sin( (double)( hpr[0] * SG_DEGREES_TO_RADIANS )) ;
    ch = (SGfloat) cos( (double)( hpr[0] * SG_DEGREES_TO_RADIANS )) ;
  }

  if ( hpr[1] == SG_ZERO )
  {
    cp = SGD_ONE ;
    sp = SGD_ZERO ;
  }
  else
  {
    sp = sin( (double)( hpr[1] * SG_DEGREES_TO_RADIANS )) ;
    cp = cos( (double)( hpr[1] * SG_DEGREES_TO_RADIANS )) ;
  }
  vec3[0] = (SGfloat)( -sh * cp ) ;
  vec3[1] = (SGfloat)( ch * cp ) ;
  vec3[2] = (SGfloat)(  sp ) ;
// rest is check
  sgVec3 hprCheck;
  sgHPRfromVec3 ( hprCheck, vec3) ;
  if(0.01<abs(hprCheck[0]-hpr[0]))
    fprintf(stderr,"\n*** Heading: %f vs %f***\n",hprCheck[0],hpr[0]);
  if(0.01<abs(hprCheck[1]-hpr[1]))
    fprintf(stderr,"\n*** Pitch: %f vs %f ***\n",hprCheck[1],hpr[1]);
  

}
--------------------- cut ------------------------------

Bye bye,
Wolfram Kuss.