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Map projection functions from standard coordinate reference system (CRS) URIs.

This library makes it easy to retrieve map projection functions from CRS URIs. It transparently fetches transformation data from http://epsg.io and uses proj4js to generate a projection out of that. Once a projection has been generated, it is stored in a local cache for later use to avoid unnecessary network requests.

uriproj also supports manually adding a projection to the local cache together with its URI, either by supplying a PROJ.4 string or a Projection object with forward() and inverse() functions.


uriproj works on browsers and any tool following the CommonJS/node module conventions.

A minified browser version of this library is available in the GitHub releases as well as on npmcdn. It can be included like that:

<script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.3.14/proj4.js"></script>
<script src="https://npmcdn.com/[email protected]/uriproj.min.js"></script>

An ES6 import would look like that:

import * as uriproj from 'uriproj'

API documentation



As an example, we load the British National Grid projection and convert geographic coordinates into projection coordinates and vice-versa.

uriproj.load('http://www.opengis.net/def/crs/EPSG/0/27700').then(proj => {
  // from WGS84 coordinates to projection coordinates
  var longitude = -1.54
  var latitude = 55.5  
  var projected = proj.forward([longitude, latitude])
  console.log('Easting: ', projected[0])
  console.log('Northing: ', projected[1])

  // back from projection coordinates to WGS84 geographic coordinates
  var geo = proj.inverse(projected)
  console.log('Longitude: ', geo[0])
  console.log('Latitude: ', geo[1])

Currently, the following URIs are recognized by load() (in addition to those stored manually with set()):

Any projection that has been previously load()'ed or stored with set() can be directly accessed via get(), avoiding the indirection of a Promise as in load():

var proj = uriproj.get('http://www.opengis.net/def/crs/EPSG/0/27700')
var projected = proj.forward([longitude, latitude])

Manually storing projections using PROJ.4 strings or projection functions is possible with set():

var uri = 'http://www.opengis.net/def/crs/EPSG/0/27700'
var proj4 = '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 ' +
   '+ellps=airy +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 +units=m +no_defs'
uriproj.set(uri, proj4)