I'm looking for a way to find the silhouette points of a planar curve when that curve is viewed from a point in the plane of the curve. In other words, looking at the curve edge-on so that it looks like a straight line I need the points on the curve that correspond with the ends of the straight line.

I want to do this both for parallel projection and projection through a point.

For parallel I tried using the BoundingBox command and Construct > Curve > Isect between the box and the curve. There's some inaccuracy though and so I end up with a couple separated points in the zone where the curve is tangent to its bounding box.

For projection through a point I can find the points manually by drawing a line through the point and then rotating the line around the point until it snaps onto a Tan snap point on the curve.

A similar manual technique works for parallel projection. I copy the curve and paste it along the view direction. Then I draw a line between the first curve and the second curve using Tan/Tan snapping. The point where the line snaps to the first curve is a silhouette point.

Finding the silhouette points is just one step in a long process that involves many curves, so I'm looking for a method that can be automated.

- Peer