transform principal moment of inertia to global coordinates

Hi,

I have a CAD program that gives the prinicpal moments of inertia and their direction (as direction cosines). I have another program that accepts an input of moments of inertia. The co-ordinate systems don't always line up, so I wanted to be able to transform these principal moments of inertia to the global co-ordinate system.

Does anyone know any good references describing how to do this? Most of what I can find is about doing things the other way (calculating the principal axes/moments of inertia).

Thanks,

[Basil C.]

Did you try using the parallel axis theorem?

Answer 1

[James Browne]

I need to rotate axis from the principal axis to new directions rather than transform it to a new position.