Thank you for your help first.
After using HiddenLine algorithms, I got the projections of all edges including OutlineEdge. But I have another problem: I want to get the adumbration of it. When I fused the VCompound(visible sharp edges) and OutLineVCompound(visible outline edges) and other visible edges, I don't know how to get borderline of this fused shape(a compound of shapes). In fact, my objective is get the projection of a shape which should be, I think, a face, right?
Can you give me some directions? Thank you in advance.
"When you make eyes in place of an eye, a hand in place of a hand, a foot in place of a foot, an image in place of an image, then you will enter." - logion