Oh, I now see they're angles indeed. What I want to point out is that the OP is doing a 180 degrees translation, while he could mean to evaluate the Principal Argument, in which case should use the transformation I propose above.

Of course, if the problem is only that of binning, for example to produce some graphics, it all reduces to choosing the correct x-axis; OTOH, if the OP wants to use these angles for some evaluations (e.g. sin, cos, stability of a system, whatever) he'd better use the correct angle wrapping function.