Should CGAL::Polygon_mesh_processing::refine() remove vertices?

[pentacular]

I expected that CGAL::Polygon_mesh_processing::refine() would just add new vertices, but I see what looks like vertex removal happening as well.

The below is expected to be a cube.

Is this expected behavior?

If not, I'll put together a minimal test case.

[sloriot]

I think there is no removal, but the placement of new vertices might be surprising.

[pentacular]

Ok, I have a pretty minimal test case.

https://gist.github.com/pentacular/2bc66d9c01439e70a32cc083a4ec61d5

It takes in a rectangular prism

And refines it to something that isn't. :)

Can you see what I am doing wrong?

[pentacular]

Ok, I had a chance to dig into this a bit deeper.

The issue is due to non-coplanar edge-flips introducing edges that cut through existing corners.

Once I add a restriction that the edge-flips be between coplanar triangles the shape is preserved as I had expected.

Is my expectation that refine should not change the shape correct, or have I misunderstood refinement?

[pentacular]

@sloriot any thoughts?