How to get object's actual rotation after freeze?

Question

Hi, how can I get object's actual rotation after freeze?

For instance :

# create a cube
CudeTransformNode = cmds.polyCube()[ 0 ]


# rotate X 20 degree.
cmds.setAttr( f"{CudeTransformNode}.rotateX" , 20 )
# * now its like 
#   - freezed rotation X : 0
#   - rotation translation X : 20
#   - actual rotation X : 20

# freeze translation.
cmds.makeIdentity( CudeTransformNode , a = 1 , r = 1 )
# * then its like 
#   - freezed rotation X : 20
#   - rotation translation X : 0
#   - actual rotation X : 20


# for test, rotate X 30 more degree.
cmds.setAttr( f"{CudeTransformNode}.rotateX" , 30 )
# * now its like 
#   - freezed rotation X : 20
#   - rotation translation X : 30
#   - actual rotation X : 50

# From here
# how to get actual rotation
Foo() == 50
# or how to get freezed rotation
Boo() == 20

** Above example, my question is how can we get the real rotation??( how to get 50 or 20 )**

Because every method I found is only telling you how to get current rotation( * rotation translation )

For reference :

• https://www.akeric.com/blog/?p=1067
• Getting rotation from matrix, OpenMaya
• Is there a way to calculate 3D rotation on X and Y axis from a 4x4 matrix

All these are telling you to use Matrix to get rotation, but the Matrix returned from native commands are always reflecting the translated values only. Therefore, in above example, the calculated output will always be 30( current rotation ).

For instance :

import maya.api.OpenMaya as om

Matrix = cmds.xform( CudeTransformNode, q = 1 , m = 1 ) 
_M = om.MMatrix( Matrix )
_TM = om.MTransformationMatrix( _M )
_rotation_radiants = _TM.rotation()

_rotation_radiants[ 0 ] <-- # equals to 30 degree

# But I want to get 20 or 50...

Maybe the question is more correct to say, how to get overall rotation matrix?

Thank you for your advices!!

Answer 1

As haggy krey has pointed out in the comments, there is no direct way to retrieve the rotation after freezing the transform, since you are applying the transformation to the components and zero out the transform node. The rotation information is simply lost.

As you mention yourself, you can determine the scale after freezing, by using the bounding box, but this only works as long as you use primitives, where their bounding box would be equivalent to applying some scale.

What exactly are you trying to accomplish?

If you are trying to restore/determine some original orientation, then you can potentially use vector math to calculate a rotation - either from two vertices, the normal vector of a face or similar. But it would require that those components align with the original rotation.

import maya.cmds as cmds

angle_vector = [0.5, 0.7, 1.0]
up_vector = [0.0, 1.0, 0.0]

euler = cmds.angleBetween(euler=True, vector1=angle_vector, vector2=up_vector)

print(euler)

Another approach could be to create some helper node (e.g., an empty group), where you don't freeze rotations. Then you could simply add or subtract the rotation of the cube and the helper node.

Finally, you could also store the original rotation in some custom attributes on the object, and add or subtract those values from the cube's current rotation.

import maya.cmds as cmds

cube = cmds.polyCube()[0]
cmds.setAttr(f"{cube}.rx", 30)

cmds.addAttr(cube, ln="originalRotationX", sn="orx", at="double", dv=0)
cmds.setAttr(f"{cube}.originalRotationX", e=True, keyable=True)  # show in Channel Box

rotationX = cmds.getAttr(f"{cube}.rx")
cmds.setAttr(f"{cube}.originalRotationX", rotationX)