public static System.Windows.Media.Media3D.Matrix3D SetSpin(
this System.Windows.Media.Media3D.Matrix3D matrix, double spin)
{
Vector3D translation = new System.Windows.Media.Media3D.Vector3D(matrix.OffsetX, matrix.OffsetY, matrix.OffsetZ);
// backoff translation
matrix.Translate(new System.Windows.Media.Media3D.Vector3D(-translation.X, -translation.Y, -translation.Z));
Vector3D localZ = matrix.Transform(new System.Windows.Media.Media3D.Vector3D(0, 0, 1));
// backoff existing spin
matrix.Rotate(new System.Windows.Media.Media3D.Quaternion(localZ, matrix.GetSpin() * -1.0));
matrix.Rotate(new System.Windows.Media.Media3D.Quaternion(localZ, spin));
// add back translation
matrix.Translate(translation);
return(matrix);
}