Hello!

I have a rotation matrix that is from a right-handed Z-up coordinate system. I am having no luck converting it into rotation angles that are usable in Houdini via Python.

What I need to know is how to convert the Matrix3 to left-handed Y-up (what I believe Houdini uses).

I'm thinking that after that I should transpose the matrix, convert it to Quaternion, then use extractEulerRotates() to get my rotation angles. Is that also correct?

When I try to reverse engineer the process by converting a scene object's Euler rotations into Quaternion and then into a rotation matrix, only the first rotate matches my initial matrix. I'm not sure where the other two columns are coming from…

Any ideas? Thanks in advance!

OK, after a lot of battling I have it working like this:

zup = zUpMatrix
zup = z.transposed()

toYup = hou.Matrix3(((1, 0, 0), (0, 0, 1), (0, -1, 0)))
yup = toYup * zup
yup = instRotation.transposed()

q = hou.Quaternion()
q.setToRotationMatrix(yup)
rotateAngles = q.extractEulerRotates()

Basically the part I was missing was transposing it TWICE. Oh – and Houdini is Y-up right handed, not left-handed as I thought earlier.