Sketch not snapping to mesh curve/facets
I imported an STL file into SpaceClaim. The STL file more or less decribes a hollow cylindrical shell. When I go to the sketch mode and want to sketch on a plane that intersects the mesh, I nicely see the blue and green lines that fit the cross section of the mesh. However I am not able to snap to these lines. As far as I know this should be possible though. I can also not project them to the sketch surface.
So basically it nicely shows the mesh curves, but I can not interact with them.
what am I doing wrong, as the manual says I should be able to snap to these lines.
Thanks in advance for your reply.