Extrude surface command question

Rhino
1

I’m trying to extrude the surface on the two surfaces in the attached file.

When I start the ExtrudeSrf command, I am only able to select small sections of the surfaces, rather than the complete surface.

Can anybody explain why this happens?

extrude surface test.3dm (3.4 MB)

2

That’s because they are not surfaces, they are open polysurfaces. To use _extrudesrf you have to use _explode first and then use _mergesrf to get 1 piece of it.

3

Thanks very much for the answer!