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WMS without Projection

Example of two WMS layers using the projection EPSG:21781, which is unknown to the client.

As long as no coordinate transformations are required, OpenLayers works fine with projections that are only configured with a code and units.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>WMS without Projection</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 {Image as ImageLayer, Tile as TileLayer} from 'ol/layer';
import Projection from 'ol/proj/Projection';
import ImageWMS from 'ol/source/ImageWMS';
import TileWMS from 'ol/source/TileWMS';


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

// A minimal projection object is configured with only the SRS code and the map
// units. No client-side coordinate transforms are possible with such a
// projection object. Requesting tiles only needs the code together with a
// tile grid of Cartesian coordinates; it does not matter how those
// coordinates relate to latitude or longitude.
var projection = new Projection({
  code: 'EPSG:21781',
  units: 'm'
});

var map = new Map({
  layers: layers,
  target: 'map',
  view: new View({
    center: [660000, 190000],
    projection: projection,
    zoom: 9
  })
});
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package.json{
  "name": "wms-no-proj",
  "dependencies": {
    "ol": "6.1.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}