I am getting start point, end point and centre point of an arc in the cartesian coordinate system. What I need to find out is the start angle (with respect to the centre point of the arc), sweep angle or delta angle (difference between end and start point in degrees with respect to the centre point of the arc) and radius (which is easy). The centre point would not always be in the origin of the cartesian coordinate system and the calculation(s) would have to account of the 4 quarters of the coordinate system.

What would be the easiest/simplest way to do this calculation?

Hope this question is in the right spot and thanks a lot for your help.