poly2

A tiny library for feature extraction of 2D polygons with focus on performance.

• Processes > 2 M small polygons per second on a single thread (Ryzen 3800X).
• As you would expect it is only for simple polygons, i.e., with no crossing edges.
• Moments are calculated using Greens theorem, and hence the orientation is important.
• The orientation can be checked with poly_vertex_order and changed with poly_reverse if needed.

Dependencies:

Only tested under 64-bit Ubuntu 21.04. For basic measurements, no special dependencies. For interpolation: gsl, for visualizations: libcairo, and libpango.

# sudo apt-cache search ...
sudo apt-get install libpangocairo-1.0-0

Lua/Löve demo

If Löve is installed, there is a small test program in src/love/ that can be run with.

cd src
make lpoly.so
love love/demo

To do or Maybe ...

• Tests!
• Clean up redundant calculations.
• Switch to CCW as the standard orientation?
• Reduce the number of calls to malloc/free.
• Polygon rasterization using the even-odd rule or nonzero winding number, see Rourke Section 7.4
• Minimal bounding box (oriented according to the principal directions).
• Smarter svg plotting with axis abstraction? Or just drop that part?

Relevant references:

• Image moments
• How to find the covariance matrix of a polygon
• Interactive demo of Melkman's algorithm