A common problem with a software 3D rendering is deciding the order in which triangles are drawn. It’s important because the most distant polygons that make up the scene should be rendered before those closer to the camera. But what about polygons that intersect?
Using this Papervision 3D tutorial, you can learn how to render 3D scene with intersecting polygons. In the demo you can switch between the basic and Quadrant rendering engines by toggling the checkbox in the top left hand corner of the screen. It makes it easy to see the difference that the Quadrant rendering engine makes. You can also download the source code for further details.