ljuillen / find-poly

A fast points(s)-in-polygons(s) test for MATLAB.

FIND-POLY: Fast point(s)-in-polygon(s) queries in MATLAB

A fast "point(s)-in-polygon(s)" routine for MATLAB / OCTAVE.

Given a collection of polygons and a set of query points, FINDPOLY determines the set of enclosing polygons for each point. Arbitrary collections of polygons and query points are supported, and general non-convex and multiply-connected inputs can be handled. FINDPOLY employs various spatial indexing + sorting techniques, and is reasonably fast for large problems.

Given K polygons (each with M edges on average) the task is to find the enclosing polygons for a set of N query points. The (obvious) naive implementation is expensive, leading to O(K*M*N) complexity (based on a simple loop over all polygons, and calling a standard points-in-polygon test for each individually). This code aims to do better:

• Employing a "fast" inpolygon routine, reducing the complexity of each point(s)-in-polygon test (based on spatial sorting) to approximately O((N+M)*log(N)).

• Employing a spatial tree (an aabb-tree) to localise each points-in-polygon query within a spatially local "tile". This typically gains another logarithmic factor, so is a big win for large K.

Quickstart

After downloading and unzipping the current repository, navigate to the installation directory within MATLAB / OCTAVE and run the examples in polydemo.m.

For good performance in OCTAVE, the underlying INPOLY kernel can be compiled from C++ as an *.oct file. See documentation on MKOCTFILE for additional information. Typically, MATLAB's in-built JIT-acceleration leads to good performance by default.

License Terms

This program may be freely redistributed under the condition that the copyright notices (including this entire header) are not removed, and no compensation is received through use of the software. Private, research, and institutional use is free. You may distribute modified versions of this code UNDER THE CONDITION THAT THIS CODE AND ANY MODIFICATIONS MADE TO IT IN THE SAME FILE REMAIN UNDER COPYRIGHT OF THE ORIGINAL AUTHOR, BOTH SOURCE AND OBJECT CODE ARE MADE FREELY AVAILABLE WITHOUT CHARGE, AND CLEAR NOTICE IS GIVEN OF THE MODIFICATIONS. Distribution of this code as part of a commercial system is permissible ONLY BY DIRECT ARRANGEMENT WITH THE AUTHOR. (If you are not directly supplying this code to a customer, and you are instead telling them how they can obtain it for free, then you are not required to make any arrangement with me.)

DISCLAIMER: Neither I nor the University of Sydney warrant this code in any way whatsoever. This code is provided "as-is" to be used at your own risk.