Moment of inertia tensor to Bullet?!

[coderJoe]

Hello,

Until now I just used the principal axes of inertia to specify my inertia (i.e. 3 values), but now I need to be able to accomodate for random shapes and random moment of inertia, thus my question:

My input is: a moment of inertia tensor. 9 elements, mirrored matrix (about the diagonal)
My desired output: the principal inertias (3 values) and a rotation matrix that specified the frame of the principal inertias

Or

Can I directly specify a moment of inertia tensor in Bullet?

Now I do it like that:

btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,collisionShape,localInertia_3Values);

[Erwin Coumans]

If you have a btMatrix3x3 inertia you can diagonalize it like this:

Code: Select all

btTransform principal;
principal.setIdentity();
btMatrix3x3 inertia(...);
tensor.diagonalize(principal.getBasis(), btScalar(0.00001), 20);
inertia.setValue(tensor[0][0], tensor[1][1], tensor[2][2]);

You will have to store your shape in a btCompoundShape so that the rigid body world transform is still aligned with the principal axis and center of mass.

See also http://code.google.com/p/bullet/source/ ... pe.cpp#214

and Bullet/Demos/FractureDemo on some example use of calculatePrincipalAxisTransform.
Thanks,
Erwin