concaveman

concaveman

A very fast 2D concave hull algorithm in JavaScript (generates a general outline of a point set).


$3

``js
import concaveman from 'concaveman';

const points = [[10, 20], [30, 12.5], ...];
const polygon = concaveman(points);
`

Signature: concaveman(points[, concavity = 2, lengthThreshold = 0])

- points is an array of [x, y] points.
- concavity is a relative measure of concavity. 1 results in a relatively detailed shape, Infinity results in a convex hull.
You can use values lower than 1, 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.

$3

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.

$3

TypeScript type definitions
are available through npm install --save @types/concaveman`.

$3

- rbush for point indexing
- tinyqueue as a priority queue
- point-in-polygon for point in polygon queries
- robust-predicates for 3-point orientation tests

$3

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).