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.

main.js

import 'ol/ol.css';
import ImageWMS from 'ol/source/ImageWMS';
import Map from 'ol/Map';
import Projection from 'ol/proj/Projection';
import TileWMS from 'ol/source/TileWMS';
import View from 'ol/View';
import {Image as ImageLayer, Tile as TileLayer} from 'ol/layer';
import {ScaleLine, defaults as defaultControls} from 'ol/control';

const layers = [
  new TileLayer({
    source: new TileWMS({
      attributions:
        '© <a href="https://shop.swisstopo.admin.ch/en/products/maps/national/lk1000"' +
        'target="_blank">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="https://www.hydrodaten.admin.ch/en/notes-on-the-flood-alert-maps.html"' +
        'target="_blank">Flood Alert / geo.admin.ch</a>',
      crossOrigin: 'anonymous',
      params: {'LAYERS': 'ch.bafu.hydroweb-warnkarte_national'},
      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.
//
// With no transforms available projection units must be assumed to represent
// true distances. In the case of local projections this may be a sufficiently
// close approximation for a meaningful (if not 100% accurate) ScaleLine control.

const projection = new Projection({
  code: 'EPSG:21781',
  units: 'm',
});

const map = new Map({
  controls: defaultControls().extend([new ScaleLine()]),
  layers: layers,
  target: 'map',
  view: new View({
    center: [660000, 190000],
    projection: projection,
    zoom: 9,
  }),
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>WMS without Projection</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <!-- The lines below are only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "wms-no-proj",
  "dependencies": {
    "ol": "6.13.1-dev"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}