>>As for the quadrants, there's always checking the sign of the segments, i.e. which is positive which is negative. Going by segments, x and y are ++, -+. --, +-.
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>Figured that out - took an old book (dated 1974)
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>But Math.Atan2( sin, cos) seems to take care of the quadrants

It probably checks the sign of the parameters to do so, so you don't have to. Nice to know it does.