1) It is relatively straightforward to compute Cartesian coordinates (x, y) on the basis of polar coordinates (r,0). The reverse process is not so simple. The radius can be computed by the following formula: If the coordinates lie within the first and fourth coordinates, i.e., x > 0, then a simple formula can be used to compute #2 tan-1 (2) The difficulty arises for the other cases. The following table summarizes the possibilities: S00tan