interior-point

Compute an interior point (representative point) of any GeoJSON geometry.

Ported from the JTS Topology Suite InteriorPoint algorithm. GeoJSON-native. The library itself has no runtime dependencies; the bundled interior-point CLI uses betterknown for WKT conversion.

Installation

npm install interior-point

Usage

import { interiorPoint } from "interior-point";

const polygon = {
  type: "Polygon",
  coordinates: [
    [
      [0, 0],
      [6, 0],
      [6, 2],
      [2, 2],
      [2, 8],
      [0, 8],
      [0, 0],
    ],
  ],
};

const point = interiorPoint(polygon);
console.log(point);
// => [1, 5]

Supported geometry types are Polygon, MultiPolygon, LineString, MultiLineString, Point, MultiPoint and GeometryCollection. An empty geometry returns null.

API

| Export | Signature | Returns | | ---------------------------- | ------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------ | | interiorPoint | (geometry: Geometry \| null) => Coordinate \| null | a point inside the geometry, or on it for lines and points | | verifyInteriorPoint | (point: Coordinate \| null, geometry: Geometry \| null) => Verification | one of "interior", "on-geometry", "off-geometry", "unverifiable" | | centroidFirstInteriorPoint | (geometry: Geometry \| null) => Coordinate \| null | the geometry's centroid when it lies strictly inside, and interiorPoint when it does not |

Coordinate is the package's re-exported alias of GeoJSON's Position. Verification runs through a point-in-polygon locator that shares no code with the algorithm that produced the point, and checks this library's own output rather than the input's OGC validity.

Full signatures, the four verification outcomes and the reasoning behind each entry point: API reference.

CLI

The package also installs an interior-point command:

npm install -g interior-point
interior-point -i "POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"
# => {"type":"Point","coordinates":[5,5]}

It reads WKT or GeoJSON — as a literal, a file, or on stdin — and writes GeoJSON by default or one WKT geometry per line. See the CLI page for every flag, the output shapes and the exit codes.

Documentation

Full documentation: https://sanak.github.io/interior-point/

Development

This library was developed with the assistance of Claude Code; every ported member is anchored to its JTS counterpart and checked against JTS's own test resources.

License

MIT

This library contains algorithms ported from JTS (EPL 2.0 / EDL 1.0).