I'd like to obtain these equations for the ellipses produced by the perspective projections of (3-dimensionally transformed) circles.
This is useful for rendering in 2D contexts which provide curve primitives. I'm using HTML5's canvas, so I get Beziers, arcs, and quadratic curves.
The projection of a sphere outside of the plane of projection is an ellipse because the view is a cone (silhouette of a sphere is a circle).
However if I want to draw my sphere using circular wireframes, that projection-cone is no longer a circular cone. So it's not your traditional conic section anymore.
How to deal with this?