Rotation for polygon

Kantronin

Hi,
I want to do a rotation for a polynone.
I know the coordinates of the points of the polygon, in the global coordinate system.
For this rotation, I know the axis of rotation, defined by a vector V, and the angle of rotation A with respect to this axis.

I manage to do this type of rotation, with matrices and with a change of Cartesian coordinate system, but I know that there is a much simpler method with C4D python functions

ferdinand

Hello @kantronin,

Thank you for reaching out to us. I am not quite sure how your last sentence is meant,

I manage to do this type of rotation, with matrices and with a change of Cartesian coordinate system, but I know that there is a much simpler method with C4D python functions

but you can define a rotation matrix from an axis of rotation v and an angle w with the function c4d.utils.RotAxisToMatrix(v, w). I.e., to transform vertices of an object, you would do something like this:

axis: c4d.Vector = c4d.Vector(1, 2, 3)
theta: float = c4d.utils.DegToRad(45)
transform: c4d.Matrix = c4d.utils.RotAxisToMatrix(axis, theta)

transformedPoints: list[c4d.Vector] = [transform * p for p in somePointObject.GetAllPoints()]

This transformation would however here happen in local object space, i.e., the space vertices/points are being expressed in. If you want to do the rotation in a space relative to the polygon, you will have to construct a frame for that polygon first, then convert the points out of local object space into your custom polygon space, carry out your rotation, and then convert the points back. I am just mentioning this because you talk about '[..] do[ing] a rotation for a polyon' which somewhat implies that you want to rotate around the origin of the polygon and some frame implied by the polygon.

Cheers,
Ferdinand

Kantronin

@ferdinand

Thanks, it works well

My first method was complex:

creation of a new orthogonal spatial system, with one of its axes is identical to the axis of rotation
compute the coordinates of the points of the object in this new spatial system, then rotate the object
calculation of the new coordinates in the initial orthogonal spatial system.