I am looking for an algorithm to simplify the meshes of buildings or similar structures.
EDIT: I had made a comment that Hoppe's algorithm tends to make meshes more and more spherical with simplification. But, I am not sure about it, so am deleting the comment. Buildings in contrast should tend to become more and more rectangular with increasing simplification. The D3DX extensions for D3D in version 9.0 (d3dx9.lib) used to have classes to do progressive mesh simplification. See: