project-geojson

Project GeoJSON files or a stream of GeoJSON or GeoJSON objects with proj4

You might not want to do this - the latest GeoJSON spec expects all GeoJSON to be in WGS84 / EPSG:4326.

However, where all involved parties have a prior arrangement, alternative coordinate reference systems can be used without risk of data being misinterpreted.

This might be useful if you want "lie to leaflet" or such like hacks to trick web mapping tools to display data in different projections. Also useful if you are parsing .shp files that are in a different coordinate system.

Table of Contents

• Install
• Usage
• API
• Known Issues
• Contribute
• License

Install

npm install --save geojson-project

Usage

project file.geojson --t_srs EPSG:3857

  Project `file.geojson` to Pseudo Mercator (`EPSG:3857`), outputs to stdout

project --t_srs EPSG:3857
project - --t_srs EPSG:3857

  Read input from stdin

options:

  -t, --t_srs <srs_def>   Destination projection, either a EPSG string or a proj4 string
  -s, --s_srs <srs_def>   Source projection, if omitted assumed to be `EPSG:4326`
  -o                      Output file, if omitted outputs to stdout

API

var projectStream = require('project-geojson')

var stream = projectStream([fromProjection,] toProjection)

Returns a transform stream that expects GeoJSON as a string or buffer and will return GeoJSON. fromProjection and toProjection can be proj or wkt strings, or EPSG strings e.g. EPSG:4326. Uses epsg-to-proj to look up EPSG codes - you will need to provide the proj or wkt string if your EPSG code is not in that database. If fromProjection is omitted it is assumed to be EPSG:4326

var objStream = projectStream.obj([fromProjection,] toProjection)

Returns an objectMode transform stream that expects and returns a stream of GeoJSON feature objects.

Example

Project the USA to Albers USA and back to WGS84 but via Pseudo Mercator - a web mapping library that projects the geojson via Psuedo Mercator will unknowingly project it to Albers USA. (N.B. I found this approx. 3x faster than doing the same with ogr2ogr)

#!/usr/bin/env node

var project = require('../')
var geojsonStream = require('geojson-stream')

var ALBERS = '+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=37.5 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs '

var wgs84ToAlbersUSA = project.obj('EPSG:4326', ALBERS)
var psuedoMercToWgs84 = project.obj('EPSG:3857', 'EPSG:4326')

process.stdin
  .pipe(geojsonStream.parse())
  .pipe(wgs84ToAlbersUSA)
  .pipe(psuedoMercToWgs84)
  .pipe(geojsonStream.stringify())
  .pipe(process.stdout)

cd example
cat usa.geojson | node example.js > usa_albers.geojson

Known Issues

It doesn't touch any bbox that might be defined on the GeoJSON, and doesn't touch any crs, which is no longer part of the current GeoJSON Spec.

Contribute

PRs accepted.

Small note: If editing the Readme, please conform to the standard-readme specification.

License

MIT © Gregor MacLennan