I’m a beginner and I could not find the answer to this simple question. How to extrude a surface from another surface like in the above image. I want to select edges and then extrude plane faces from them so as to have a new surface emerge from an existing surface.
The cleanest method would be to duplicate the sphere, move it’s vertices as needed to create the shape of the plane, and then delete all the other faces. This would treat the plane as a different object, although you can then merge the subtools back together (in which case the plane will just be a disconnected polygon island).
Otherwise you’d be into non-manifold geometry, which zbrush may not even support (and probably rightly so).