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Single Image WMS with Proj4js

Example of integrating Proj4js for coordinate transforms.

With Proj4js integration, OpenLayers can transform coordinates between arbitrary projections.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Single Image WMS with Proj4js</title>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="index.js"></script>
  </body>
</html>
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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import {defaults as defaultControls, ScaleLine} from 'ol/control';
import ImageLayer from 'ol/layer/Image';
import {fromLonLat} from 'ol/proj';
import Projection from 'ol/proj/Projection';
import ImageWMS from 'ol/source/ImageWMS';
import {register} from 'ol/proj/proj4';
import proj4 from 'proj4';


// Transparent Proj4js support:
//
// EPSG:21781 is known to Proj4js because its definition is registered by
// calling proj4.defs(). Now when we create an ol/proj/Projection instance with
// the 'EPSG:21781' code, OpenLayers will pick up the transform functions from
// Proj4js. To get the registered ol/proj/Projection instance with other
// parameters like units and axis orientation applied from Proj4js, use
// `ol/proj#get('EPSG:21781')`.
//
// Note that we are setting the projection's extent here, which is used to
// determine the view resolution for zoom level 0. Recommended values for a
// projection's validity extent can be found at https://epsg.io/.

proj4.defs('EPSG:21781',
  '+proj=somerc +lat_0=46.95240555555556 +lon_0=7.439583333333333 +k_0=1 ' +
    '+x_0=600000 +y_0=200000 +ellps=bessel ' +
    '+towgs84=660.077,13.551,369.344,2.484,1.783,2.939,5.66 +units=m +no_defs');
register(proj4);

var projection = new Projection({
  code: 'EPSG:21781',
  extent: [485869.5728, 76443.1884, 837076.5648, 299941.7864]
});

var extent = [420000, 30000, 900000, 350000];
var layers = [
  new ImageLayer({
    extent: extent,
    source: new ImageWMS({
      url: 'https://wms.geo.admin.ch/',
      crossOrigin: 'anonymous',
      attributions: '© <a href="http://www.geo.admin.ch/internet/geoportal/' +
          'en/home.html">Pixelmap 1:1000000 / geo.admin.ch</a>',
      params: {
        'LAYERS': 'ch.swisstopo.pixelkarte-farbe-pk1000.noscale',
        'FORMAT': 'image/jpeg'
      },
      serverType: 'mapserver'
    })
  }),
  new ImageLayer({
    extent: extent,
    source: new ImageWMS({
      url: 'https://wms.geo.admin.ch/',
      crossOrigin: 'anonymous',
      attributions: '© <a href="http://www.geo.admin.ch/internet/geoportal/' +
          'en/home.html">National parks / geo.admin.ch</a>',
      params: {'LAYERS': 'ch.bafu.schutzgebiete-paerke_nationaler_bedeutung'},
      serverType: 'mapserver'
    })
  })
];

var map = new Map({
  controls: defaultControls().extend([
    new ScaleLine()
  ]),
  layers: layers,
  target: 'map',
  view: new View({
    projection: projection,
    center: fromLonLat([8.23, 46.86], projection),
    extent: extent,
    zoom: 2
  })
});
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package.json{
  "name": "wms-image-custom-proj",
  "dependencies": {
    "ol": "6.1.1",
    "proj4": "2.5.0"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}