Hi there, I am getting confused about how to work this out. I know that to convert cartesian coordinates to spherical coordinates you can use: theta=arccos(z) phi=arcsin(y/sin(theta)) my problem is that I have a list of coordinates, lets call them THETA and PHI. I change them into X,Y,Z and then rotate them by 2 Euler angles. THETA is in the range(0->2pi) PHI is in the range (-pi/2->pi/2). the problem is once I have completed the transforms I want the new value theta, As it is found using arccos the value returned is only in the range 0->pi, the values come back between 0 and 180, where as the THETA values are between 0 and 360, and therefore I want my transformed values to be in the range 0 to 360. I think I need to use quadrants but I have been searching the internet and can't find the info I need. Any help would be greatly appreciated.