Find the start, sweep and end angles of an arc within its own plane.

Input parameters:

1. Ar → Arc to dissect.

Output parameters:

1. As → Angle of the start of the arc, as measured anti-clockwise from the arc plane x-axis.
2. Aw → Angle of the interior of the arc, as measured anti-clockwise within the arc plane.
3. Ae → Angle of the end of the arc.