# polylabel

**Repository Path**: lengjianjun/polylabel

## Basic Information

- **Project Name**: polylabel
- **Description**: 从 https://github.com/mapbox/polylabel 克隆。Polylabel是Mapbox开源的C++/JavaScript库，用于快速计算多边形视觉中心点。它采用四叉树算法，在保证精度的同时高效求解最大内切圆圆心，解决复杂凹多边形的标注定位问题。相比质心法，结果更符合人类视觉感知，广泛应用于地图标签、图标放置等场景。项目轻量无依赖，支持WASM，采用ISC许可证。
- **Primary Language**: Unknown
- **License**: ISC
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2026-08-05
- **Last Updated**: 2026-08-05

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

## polylabel [![CI](https://github.com/mapbox/polylabel/actions/workflows/test.yml/badge.svg)](https://github.com/mapbox/polylabel/actions/workflows/test.yml) [![Simply Awesome](https://img.shields.io/badge/simply-awesome-brightgreen.svg)](https://github.com/mourner/projects)

A fast algorithm for finding polygon _pole of inaccessibility_,
the most distant internal point from the polygon outline (not to be confused with centroid),
implemented as a JavaScript library.
Useful for optimal placement of a text label on a polygon.

It's an iterative grid algorithm,
inspired by [paper by Garcia-Castellanos & Lombardo, 2007](https://sites.google.com/site/polesofinaccessibility/).
Unlike the one in the paper, this algorithm:

- guarantees finding **global optimum** within the given precision
- is many times faster (10-40x)

![](https://cloud.githubusercontent.com/assets/25395/16745865/864a0a30-47c0-11e6-87bc-58acac41a520.png)

### How the algorithm works

This is an iterative grid-based algorithm, which starts by covering the polygon with big square cells and then iteratively splitting them in the order of the most promising ones, while aggressively pruning uninteresting cells.

1. Generate initial square cells that fully cover the polygon (with cell size equal to either width or height, whichever is lower). Calculate distance from the center of each cell to the outer polygon, using negative value if the point is outside the polygon (detected by ray-casting).
2. Put the cells into a priority queue sorted by the maximum potential distance from a point inside a cell, defined as a sum of the distance from the center and the cell radius (equal to `cell_size * sqrt(2) / 2`).
3. Calculate the distance from the centroid of the polygon and pick it as the first "best so far".
4. Pull out cells from the priority queue one by one. If a cell's distance is better than the current best, save it as such.
Then, if the cell potentially contains a better solution that the current best (`cell_max - best_dist > precision`),
split it into 4 children cells and put them in the queue.
5. Stop the algorithm when we have exhausted the queue and return the best cell's center as the pole of inaccessibility.
It will be guaranteed to be a global optimum within the given precision.

![image](https://cloud.githubusercontent.com/assets/25395/16748630/e6b3336c-47cd-11e6-8059-0eeccf22cf6b.png)

### JavaScript Usage

Given polygon coordinates in
[GeoJSON-like format](http://geojson.org/geojson-spec.html#polygon) (an array of arrays of `[x, y]` points)
and precision (`1.0` by default),
Polylabel returns the pole of inaccessibility coordinate in `[x, y]` format. The distance to the closest polygon point (in input units) is included as a `distance` property.

```js
const p = polylabel([[[0, 0], [1, 0], ...]], 1.0);
const distance = p.distance;
```

Be careful to pick precision appropriate for the input units. E.g. in case of geographic coordinates (longitude and latitude), `0.000001` is appropriate, while the default (`1.0`) would be too imprecise.

### TypeScript

[TypeScript type definitions](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/polylabel)
are available via `npm install --save @types/polylabel`.

#### Ports to other languages

- [andrewharvey/geojson-polygon-labels](https://github.com/andrewharvey/geojson-polygon-labels) (CLI) 
- [Twista/python-polylabel](https://github.com/Twista/python-polylabel) (Python)
- [Shapely](https://github.com/Toblerity/Shapely/blob/master/shapely/algorithms/polylabel.py) (Python)
- [polylabelr](https://CRAN.R-project.org/package=polylabelr) (R)
- [polylabel-rs](https://github.com/urschrei/polylabel-rs) (Rust)
- [php-polylabel](https://github.com/dliebner/php-polylabel) (PHP)
- [dart_polylabel](https://github.com/beroso/dart_polylabel) (Dart)
- [ruby-polylabel](https://github.com/fredplante/ruby-polylabel) (Ruby)
- [Polylabel.jl](https://github.com/asinghvi17/Polylabel.jl) (Julia)
- [geobase](https://github.com/navibyte/geospatial/blob/main/dart/geobase/lib/src/geometric/cartesian/areal/polylabel.dart) (Dart)
- [PolylabelNet](https://github.com/oberbichler/PolylabelNet) (C#)
- [polylabel-geometrynodes](https://github.com/farukahmet/polylabel-geometrynodes) (Blender)