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concaveman

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Fast 2D concave hull algorithm in JavaScript (generates an outline of a point set)

github.com/mapbox/concaveman

mapbox/concaveman

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## concaveman A very fast **2D concave hull** algorithm in JavaScript (generates a general outline of a point set). [![Build Status](https://travis-ci.org/mapbox/concaveman.svg?branch=master)](https://travis-ci.org/mapbox/concaveman) [![Coverage Status](https://coveralls.io/repos/github/mapbox/concaveman/badge.svg?branch=master)](https://coveralls.io/github/mapbox/concaveman?branch=master) [![](https://img.shields.io/badge/simply-awesome-brightgreen.svg)](https://github.com/mourner/projects) <img width="570" alt="sample concave hull" src="https://cloud.githubusercontent.com/assets/25395/12975726/ada2ad10-d0c6-11e5-96c8-6e42c995e0e2.png"> ### Usage ```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. ### Algorithm The algorithm is based on ideas from the paper [A New Concave Hull Algorithm and Concaveness Measure for n-dimensional Datasets, 2012](https://jise.iis.sinica.edu.tw/JISESearch/fullText?pId=245&code=5A9B97538372AA1) 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 [TypeScript type definitions](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/concaveman) are available through `npm install --save @types/concaveman`. ### Dependencies - [rbush](https://github.com/mourner/rbush) for point indexing - [tinyqueue](https://github.com/mourner/tinyqueue) as a priority queue - [point-in-polygon](https://github.com/substack/point-in-polygon) for point in polygon queries - [robust-predicates](https://github.com/mourner/robust-predicates) for 3-point orientation tests ### C++ Port In 2019, a [C++ port](https://github.com/sadaszewski/concaveman-cpp) 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).