Revit Longshot question about Ellipses

Licensed architect in Northeast USA right here.

Been utilizing Revit for about 10 years now, and understand it inside and outside, however am having bother with one particular train.

Hoping past hope some Revit wiz can present me how to attract a geometrically excellent elipse in Revit. By geometrically excellent I imply that there are two focal factors, and the sum of each radii as they meet at any level alongside the perimeter of the ellipse is fixed.

Re: Diagram Above.

I do know Revit has an ellipse perform for element strains, however I see no possibility for figuring out focal factors or radii. The ellipses in Revit are junk for what I'm making an attempt to realize.

In an ideal world, there can be a parametric household that creates an elipse based mostly on the offered values.

My honest gratitude upfront for anybody who may also help.