A very fast 2D concave hull algorithm in JavaScript (generates a general outline of a point set).
var points = [[10, 20], [30, 12.5], ...];
var polygon = concaveman(points);Signature: concaveman(points[, concavity = 2, lengthThreshold = 0])
pointsis an array of[x, y]points.concavityis a relative measure of concavity.1results in a relatively detailed shape,Infinityresults in a convex hull. You can use values lower than1, but they can produce pretty crazy shapes.lengthThreshold: when a segment length is under this threshold, it stops being considered for further detalization. Higher values result in simpler shapes.
The algorithm is based on ideas from the paper A New Concave Hull Algorithm and Concaveness Measure for n-dimensional Datasets, 2012 by Jin-Seo Park and Se-Jong Oh.
This implementation dramatically improves performance over the one stated in the paper
(O(rn), where r is a number of output points, to O(n log n))
by introducing a fast k nearest points to a segment algorithm,
a modification of a depth-first kNN R-tree search using a priority queue.
TypeScript type definitions
are available through npm install --save @types/concaveman.
- monotone-convex-hull-2d for the convex hull algorithm
- rbush for point indexing
- tinyqueue as a priority queue
- point-in-polygon for point in polygon queries
- robust-orientation for 3-point orientation tests
In 2019, a C++ port has been created, allowing for efficient usage from C/C++, Python (via cffi) and other languages featuring an FFI and/or plug-in mechanism for C (e.g. a MATLAB MEX file should be easy to prepare).