Crows can recognize geometric patterns, suggesting that humans aren't unique in understanding shape structure.

Mathematicians’ Favorite Shapes Hold the Key to Big Mathematical Mysteries ...

Don't be surprised if you see some of these items in your friend's house the next time you visit them. View Entire Post › ...

C++ 2D geometry library, handles points, lines, polylines, planar transformations (and other primitives), using homogeneous coordinates. Provided with complete manual and samples.