concaveman

What is concaveman?

Concaveman is a very fast 2D concave hull algorithm that is used to compute the concave hull of a set of 2D points. It is particularly useful in computational geometry for tasks such as shape analysis, clustering, and spatial data visualization.

What are concaveman's main functionalities?

Compute Concave Hull

This feature allows you to compute the concave hull of a set of 2D points. The code sample demonstrates how to use the concaveman package to calculate the concave hull for a given set of points.

const concaveman = require('concaveman');
const points = [[10, 10], [20, 20], [30, 10], [40, 40], [50, 30]];
const concaveHull = concaveman(points);
console.log(concaveHull);

Other packages similar to concaveman

hull.js

Hull.js is a JavaScript library for computing the convex hull of a set of 2D points. Unlike concaveman, which computes a concave hull, hull.js focuses on convex hulls, which are the smallest convex shape that can enclose all the points.

alpha-shape

Alpha-shape is a library for computing the alpha shape (a generalization of the convex hull) of a set of points. It provides more flexibility in defining the shape of the hull compared to concaveman, which strictly computes concave hulls.

d3-polygon

D3-polygon is part of the D3.js library and provides utilities for polygon geometry, including computing the convex hull of a set of points. While it is more general-purpose and part of a larger visualization library, it does not specifically focus on concave hulls like concaveman.

README

concaveman

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

Usage

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 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 are available through npm install --save @types/concaveman.

Dependencies

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

C++ Port

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).