Just a quick update. I've got a pretty good start on the UML diagram for the foundation of the geometry module. You can get to it by following the My SymPy Workings link to the right or go to it directly by clicking here. This is just an initial, very basic diagram for the moment, and some things aren't really descried in the diagram. For example, Some things I have as methods but they might really be attributes fetched by an overloaded __getattr__ operator (eg, area for Polygons and Ellipses).
Any feedback on the current diagram, or suggestions for additions, would be great. Now, it's time for bed!