Extract rotation / scale / position from IFC openshell transformation matrix python

B by baldash on 21 Apr 2021, edited 21 Apr 2021 #

Hi all !

I'm a beginner to IFC files and transformation matrices and wondered I could extract rotation / scale and position from a transformation matrix using python.

I'm using ifcopenshell and shape.transformation.matrix.data gives me this :

(-1.0, 0.0, 0.0, 0.0, -1.0, 0.0, 0.0, 0.0, 1.0, 8.382999999999972, -17.5915, 0.0)

So, now from this tuple I know that the matrix is supposedly mapped like this :

matrix([[ -1. , 0. , 0. , 8.383 ],

    [  0.    ,  -1.    ,   0.    , -17.5915],

    [  0.    ,   0.    ,   1.    ,   0.    ],

    [  0.    ,   0.    ,   0.    ,   1.    ]])

But I don't know how to obtain this matrix and how to extract the data I want from it. I'm supposed to get :

rotation (x,y,z) : 0, 0, 180

scale : 1, 1, 1

location ; 8.3, -17.5, 0

So any idea on how to do it using ifcopenshell and python ?

Thanks!

B by brunopostle on 21 Apr 2021, edited 21 Apr 2021 #

There is probably a numpy function that will do this for you, but a transformation matrix for a location (coor) and 2D rotation (theta) looks like this:

    [

        [cos(theta), 0.0 - sin(theta), 0.0, coor[0]],

        [sin(theta), cos(theta), 0.0, coor[1]],

        [0.0, 0.0, 1.0, coor[2]],

        [0.0, 0.0, 0.0, 1.0],

    ]

B by baldash on 21 Apr 2021 #

Thanks for your answer ! But in my case it's for a 3D environment

L by LaurensJN on 21 Apr 2021 # +1 votes

If you need Euler angles, you can use the left upper 3x3 matrix as rotation matrix. I don't think numpy has a method for this but scipy.spatial.transform.Rotation.as_euler is the method from SciPy you could use.

Translation/position is as @brunopostle said the right side of the matrix.

For scale (don't pin me on this) you can extract each component (X, Y, Z) by computing the magnitude of respectively the first, second and third column of the matrix.

B by baldash on 21 Apr 2021 #

After some research and many help from Dion Moult on ifcopenshell's github, I used mathutils matrix in order to get all the data I needed, thanks for the help !

M by Moult on 21 Apr 2021 # +2 votes

Linking to the bugreport for those interested: https://github.com/IfcOpenShell/IfcOpenShell/issues/1440