Rotation matrix workflow

[Justin Israel]

Hey all.

My current project right now has an aspect which is not my forté. Hopefully you guys with strong matrix manipulation skills can advise the "pipeline" guy...

I'm dev'ing a library that reads and delivers Kinect sensor data to Maya. The joint orientation data is delivered as 3x3 rotation matrices. As of now to get the concept working, I am converting them to Euler on the library side (via cgkit), and then piping them into maya over my socket. Within Maya, for this specific example, I am just interested in applying the rotZ to my component. And I am doing that very basically right now with a rotate command to see live results. 

What I would like to do is just send my 3x3 rotation matrix in its raw form and apply the rotZ via the API to the rotation of the transform. I will always be applying transformations by discrete axis (usually I only care about rz, and for translation I only care about tx/ty).

Can someone give me a quick workflow suggestion of 3x3 rotation matrix -> add rz to QTransformationMatrix ?

I know I will need to pad it out to 4x4, and create an MMatrix, but once I have that I am pretty weak on the concept of the matrix operations.

[Adam Mechtley]

Hi Justin,

I'm not 100% clear on the needs (i.e., why only one axis is desired, which prevents you from using a much cleaner quaternion-based solution), but if you're only wanting to extract rotation about a single axis from a matrix that has rotation about all three axes, then you need to select some decomposition order if you want it as Euler angles (e.g., XYZ, ZXY, etc.)—probably just whatever is being used by the transform you are piping it to. In Maya, there is an MTransformationMatrix constructor that accepts an MMatrix. Thereafter, you can call reorderRotation on the transformation matrix to set your desired decomposition order and simply get its eulerRotation.

Sorry if I missed what you need to do a bit, but hopefully there's something helpful here

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[Justin Israel]

Our rigs only move in XY and rotate in Z, so the sensor data has information I don't always want to apply. Ultimately I have to map the raw sensor data to different axis based on various conditions. I get what you are saying so far, and I just wanted to make sure this is the most efficient approach:

1. Raw data -> MMatrix -> Euler -> Euler.z

2. get objects MTransformationMatrix -> euler

3. Set objects euler.z = to this euler.z

4. MTransMatrix setRotation( updated euler )

I was just doubting myself because of the number of objects and conversions and thought there was some better way that I was missing. 

[Adam Mechtley]

Well not quite sure that's what I had in mind. Maybe this is easier ;)

import Maya.OpenMaya as om

matrix = om.MMatrix() # has index operator

# set matrix elements from sensor data using index operator here

transformation_matrix = om.MTransformationMatrix(matrix) # has no index operator, but has methods for getting rotation

transformation_matrix.reorderRotation(om.MTransformationMatrix.kZXY) # or whatever rotation order you need

euler_rotation = transformation_matrix.eulerRotation()

z_rotation = euler_rotation.z # note: this is in radians

# do whatever you need to do with z_rotation,

# such as create new MEulerRotation and apply

# to another transform with MFnTransform.setRotation()

[Justin Israel]

Cool. Looks about like what I have now, aside from using an MScriptUtil to create the MMatrix from the raw data.

Thanks for the clarification!