[ODE] dMassSetCylinder() and dMassSetCone()

[Michael Bailey]

Hi All,

I'm trying to duplicate the ODE mass functions for a (non-capped) cylinder
and a cone.  The ODE mass functions have a lot of strange constants when
calculating the "inertia matrix", of which I haven't a clue what's going on
there.  Can anyone who understands what needs to be filled in the dMass
struct, check these out and give me some feedback?

Thanks in advance!

Mike


// A doctored version of the original ODE dMassSetCappedCylinder(), not sure
if the inertia matrix is right.

void dMassSetCylinder(dMass *m, dReal density, int direction, dReal aRad,
dReal bLen)	{

  dReal M1,Ia,Ib;
  dAASSERT (m);
  dUASSERT (direction >= 1 && direction <= 3,"bad direction number");
  dMassSetZero (m);
  M1 = M_PI*aRad*aRad*bLen*density;		// cylinder mass
  m->mass = M1;
  Ia = M1*(REAL(0.25)*aRad*aRad + (REAL(1.0)/REAL(12.0))*bLen*bLen);
  Ib = (M1*REAL(0.5));
  m->_I(0,0) = Ia;
  m->_I(1,1) = Ia;
  m->_I(2,2) = Ia;
  m->_I(direction-1,direction-1) = Ib;
}

// Have no clue what to do for the inertia matrix here!

void dMassSetCone(dMass *m, dReal density, int direction, dReal aBaseRad,
dReal bLen)	{

  dReal M1,Ia,Ib;
  dAASSERT (m);
  dUASSERT (direction >= 1 && direction <= 3,"bad direction number");
  dMassSetZero (m);
  M1 = ((M_PI*aBaseRad*aBaseRad*bLen)/REAL(3.0))*density;		// cone mass
  m->mass = M1;


  // ?? I Have no idea how to set up the inertia matrix for a cone!

}