Tessellation callbacks

I’m trying to convert build engine (duke3d / blood / shadow warrior / etc) maps into quake format. I was turned on to OpenGL tessellation as a possible solution for breaking concave sectors into multiple convex shapes.
So far, I’m able to lay out my code ok.
Create tess object, define callbacks, define vertices, end.
My problem is with the callbacks, and getting the triangles from the tessellator. I know I’m going to have to use vertexData(), but right now all my callbacks are stubs (empty functions).
Any ideas how to get the triangle data back?