My problem is that I must find from a 3d matrix(that is an input from a .ifc file bim) the rotation component around the axis of extrusion vector (that i have). If you multiply all the 2d profile points for the rotation matrix or if i find the angle with Eulers , is correct only for a beam or column oriented in x/y plane If i change the extruding direction i change the x,y,z of the multiplied 2d points(the profile of the section) for example a point is 122,122,0 for the z direction : 0, 122 ,122 or for a y direction: 122, 0 , 122 or x 122,122,0 ecc....... in the rotation matrix there is the rotation of the profile(around the z axis) and the rotation of the beam profile. How i can extract only the section rotation angle? I see that is sufficient get the correct pair of coords , but how i can create an algorithm in c++ that select the correct coordinates pairs? x,y x,z or y,z?