Round of a half cut cylinder with subsurf im trying to model a half cut cylinder with an axial cut section. The Cylinder has a subsurf modifier. As long as the cylinder is cylindrical, it is perfectly round (Type A). If i remove the half of the cylinder using a boolean operation, it stays round (B). But if i remove the verts in edit mode, the shape is no longer round (C ):



Is there a way to model a shape like C without a boolean modifier? The problem is that the cylinder i part of a larger model, and if i cut it, the topology gets destroyed:


Using the Boolean Modifier alone is not a solution as the model should be low poly and be exported into another application.

Thank you for help!
Add a cylinder;
Apply E and S to the bases and delete created faces. Remove doubles;
Join the edges with Bridge Edge Loops to make inner faces. The result should look as below;

In face selection mode select, with B, and delete half of the cylinder created thus;
Make faces where the crossection was made (see the image below);



Done.

If you want you may make more quads with Ctrl+R