This is a really basic question, yet I can't remember my old geometry classes nor could I find an answer via google.
Given a circle "tilted" at angle a to the horizontal plane, and given angle b inside the circle, I want to calculate the vertically projected angle, c, on the horizontal plane.
It's obvious that the circle's vertical projection on the plane is an ellipse, and that cos(b) = cos(c) but I still can't work out the formula that gives me c given only the 2 first angles.
I'm assuming this can be worked out regardless of the dimensions of the circle, although temporary arbritary dimensions can be used to calculate the solution.
Note: As an example, in the above sketchup drawing a = 70 degrees, b = 45 degrees, and (what I want to calculate mathematically) c = 18.8 degrees.