I need to work out the elipse a half circle that is vertical leaves on to a pitched surface

Question

Say the half circle had a radius of 800mm and it was casting back of to a pitched line of 45 degrees it would leave an elipse how do i work that out ?

And is therr a set formula so i can change the angle and the radius

Answer 1

Assume that the radius of the circle is "r."

Then the major axis of the ellipse is 2r and the minor axis r√2.

From these you can "work out the ellipse."