How to calculate the start and end point of an elliptical arc from given angles

For a long description, example document and screenshots see mail https://www.oasis-open.org/apps/org/workgroup/office/email/archives/201304/msg00002.html

This is about commands U and T in draw:enhanced-path (19.145, part 1, ODF 1.2). The arc is defined by a start and an end angle. But the specification does not say, how to create the points. There exists two reasonable methods, which are used by applications.
(1) Intersect leg of the angle with the full ellipse.
(2) Intersect leg of the angle with the corresponding outer circle and scale the circle then to get the ellipse.

I think that the problem has to be discussed with OIC and people of the affected applications. I have no proposal.