This task shows how to create silhouette edges to be used in sketches as geometry or reference elements.  
You can only create a silhouette edge from a canonical surface whose axis is parallel to the Sketch plane.  
Open the Silhouette_Edge.CATPart document.  






The silhouette edges are created onto the sketch plane.
These silhouette edges are yellow if they are associative with the 3D. You cannot move or modify them but you can delete one of them which means deleting one trace independently from the other. 

You can select one of the two
intersections and set it into the Construction mode:

You can create geometry and constraints using this intersection:


You can relimit this created silhouette edge using the geometry: 

The silhouette command generated one or two marks (edges) if one mark is made of more that one curves. If those curves do not have the same geometrical support, the resulting silhouette edges will not be associative (as for Projection/Intersection commands).  



