liveby / geojson-polyline

Convert GeoJSON coordinates to and from encoded polylines. Supports all major GeoJSON types.

GeoJSON PolyLine

Convert GeoJSON coordinates to and from encoded polylines. Supports encoding or decoding geometries/coordinates for all 9 standard GeoJSON types. Use it in Node.js (optionally as a transform stream), in the browser, as a Web Worker, or from the command line.

Install

npm install geojson-polyline

Usage

encode(geoJSON[, options])

Convert a GeoJSON object's coordinates to encoded polylines.

• geoJSON : A GeoJSON object (required).
• options : An optional Object with the following possible properties:
  • precision: A Number specifying the number of digits to keep for lat/lon. Default is 5.

Aliases: polyline, polyLine, toEncoded, fromGeoJSON, toPolyline.

Example

const encode = require('geojson-polyline').encode
const polygon = {
  type: 'Polygon',
  coordinates: [
    [[-81.63829, 41.48093], [-81.63628, 41.47993], [-81.63625, 41.47931], [-81.63829, 41.48033], [-81.63829, 41.48093]]
  ]
}
const encoded = encode(polygon)
// => { type: 'Polygon', coordinates: ['yvd|Fh~gqNfEqKzBEkEvKwB?'] }

decode(polyGeo[, options])

Convert a polyline-encoded GeoJSON to standard GeoJSON coordinate arrays.

• polyGeo : A GeoJSON object whose coordinates are expressed as polylines (required).
• options : An optional Object with the following possible properties:
  • precision: A Number specifying the precision that the polyline was encoded with. Default is 5.

Aliases: decode, geojson, geoJson, geoJSON, fromEncoded, toGeoJSON fromPolyline.

Example

const decode = require('geojson-polyline').decode
const polygon = {
  type: 'Polygon',
  coordinates: ['yvd|Fh~gqNfEqKzBEkEvKwB?']
}
const geoJSON = decode(polygon)
// => { type: 'Polygon', coordinates: [[[-81.63829, 41.48093], [-81.63628, 41.47993], [-81.63625, 41.47931], [-81.63829, 41.48033], [-81.63829, 41.48093]]]}

Stream API

Use the streaming API if you have streams instead of objects. Outputs newline-separated JSON.

Usage

var encode = require('geojson-polyline/stream').encode
// var decode = require('geojson-polyline/stream').decode

fs.createReadStream('./tl_2016_33_place.geojson')
  .pipe(encode({precision: 4}))
  .pipe(process.stdout)

Browser Usage

Standalone builds are available in /dist for in-browser usage, which are ES3 compatible.

<script src="dist/geojson-polyline.min.js"></script>
<script>
  var decoded = encoded.map(GeoJSONPolyline.decode);
</script>

Web Worker

If you want to decode polylines using Web Workers, that is supported out of the box:

var worker = new Worker('dist/geojson-polyline.min.js')
var decoded = []
encoded.forEach(function(encoded){
  worker.postMessage(['decode', encoded])
})
worker.onmessage = function(event) {
  decoded.push(event.data)
  if(decoded.length === encoded.length) {
    // Done!
  }
}

Currently, decoding and encoding is faster in the browser without using Web Workers.

Command Line Interface (CLI)

Convert GeoJSON objects, features, and feature collections from the command line. Works great for .geojson files from ogr2ogr or shp2json.

Install

npm install --global geojson-polyline

Usage

Usage:
  geojson-polyline <command> (read from stdin)
  geojson-polyline <command> -f <file> [<file2>] [...]
  geojson-polyline <command> <input>

Convert the coordinates of a GeoJSON object to and from encoded polylines. 

In all cases, input should be a valid JSON object or newline-separated JSON. 

Command is one of:
  encode
  decode
  geojson
  geoJson
  geoJSON
  polyline
  polyLine
  toEncoded
  fromEncoded
  toGeoJSON
  fromGeoJSON
  toPolyline
  fromPolyline

Example

geojson-polyline encode -f tabblock2010_56_pophu.geojson | mongoimport -c tabblock2010

Additional Information

Google's encoded polyline algorithm provides for very efficient encoding and storage of coordinate data. The @mapbox/polyline library from MapBox provides an implementation to encode/decode polylines, but only supports GeoJSON "LineString" features, not "Polygons" or "MultiLineStrings".

License

ISC