# Uniform or Rigid Rotation

Uniform or rigid rotation is a special case of nonuniform rotation in which both the x- and y-coordinate axes rotate by an equal angle. The following figure shows two coordinate spaces uniformly rotated with respect to each other.

You measure the rotation angle θ from coordinate space B and express its sign relative to space B. For example, the rotation angle shown in the preceding figure is about -20 degrees or -0.349 radians. You can map the coordinates of P in space A to the corresponding coordinates in space B with the following transformation:

Note that the rotation angle θ is the angle from space B to space A as measured in B.