geos-wasm

This is a WebAssembly build of GEOS using Emscripten. It can be used in the browser or in Node.js, bun, or deno.

GEOS is a C/C++ port of the Java Topology Suite, a library for performing operations on planar geometry. GEOS provides many of the algorithms used by PostGIS, the Shapely package for Python, the sf package for R, and others.

Demo • API Documentation

Installation

Browser

<script type="module">
  import initGeosJs from './build/package/geos.esm.js';
  const geos = await initGeosJs();
</script>

Node.js

import initGeosJs from './src/index.mjs';
const geos = await initGeosJs();

Example

import initGeosJs from '../../build/package/geos.esm.js'
// initGeosJs returns a promise that resolves to a GEOS object
const geos = await initGeosJs()

// use the GEOS object to call GEOS functions
// Example: get the area of a polygon
// create a WKT reader
const reader = geos.GEOSWKTReader_create()
const wkt = 'POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))'
// read the WKT string into a GEOS geometry -> returns a pointer
const size = wkt.length + 1
const wktPtr = geos.Module._malloc(size)
geos.Module.stringToUTF8(wkt, wktPtr, size)
const geomPtr = geos.GEOSWKTReader_read(reader, wktPtr)
// create a pointer where the area will be written to
const areaPtr = geos.Module._malloc(8)
// calculate the area of the geometry
geos.GEOSArea(geomPtr, areaPtr)
// read the area from the pointer into a JS number
const area = geos.Module.getValue(areaPtr, 'double')

console.log(area) // area = 1

// free the WKT reader, the geometry, and the pointers
geos.GEOSWKTReader_destroy(reader)
geos.GEOSGeom_destroy(geomPtr)
geos.GEOSFree(areaPtr)
geos.Module._free(wktPtr)

API

Please refer to the API documentation.

Development

Prerequisites

Compiling

The compiling process and overall project structure is largely copied from gdal3! Thanks for the great work!

Clone the repository.
Run npm install.
Run npm run make or make. Run make type=debug for a debug version.

Testing

npm test

Contribution

Contributions are welcome! Please open an issue in order to discuss contributions before submitting a pull request.

chrispahm/geos-wasm