----Original Message---- From: Anis Benyelloul [mailto:benyelloul@mailbolt.com]

" There is no such a thing as a 2D point, There is even no such a thing as 2D, the world is 3D, and all points are 3D. Now, some point are always located on Z=0 plan and don't need to actually store their Z attribute, we call them 2D points."

Actually one of the current popular physical theories is that the world is 11D (or is it 15?). [Snip]

...

Mixing 2D and 3D points doesnt actually happen in my experience. They live in separate spaces. Like I say, 2D points are elements of IRxIR which is U which is part of IRxIRxIR which is the set of all 3D points. It just a matter of how you look at things ..

Yes, but insisting that people consider 2D points a subset of 3D points (rather than a different concept which is isomorphic with a subset of 3D points), is probably a mistake. -- Martin Bonner Martin.Bonner@Pitechnology.com Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ, ENGLAND Tel: +44 (0)1223 441434