How to calculate the angle from rotation matrix

We can get Euler angles from rotation matrix using following formula.

Given a 3×3 rotation matrix

enter image description here

The 3 Euler angles are

enter image description here

enter image description here

enter image description here

Here atan2 is the same arc tangent function, with quadrant checking, you typically find in C or Matlab.

Note: Care must be taken if the angle around the y-axis is exactly +/-90°. In that case all elements in the first column and last row, except the one in the lower corner, which is either 1 or -1, will be 0 (cos(1)=0). One solution would be to fix the rotation around the x-axis at 180° and compute the angle around the z-axis from: atan2(r_12, -r_22).

See also https://www.geometrictools.com/Documentation/EulerAngles.pdf, which includes implementations for six different orders of Euler angles.

Leave a Comment