OpenLayers
OpenLayers
Example of integrating Proj4js for coordinate transforms.
With Proj4js integration, OpenLayers can transform coordinates between arbitrary projections.
import ImageLayer from 'ol/layer/Image.js';
import ImageWMS from 'ol/source/ImageWMS.js';
import Map from 'ol/Map.js';
import Projection from 'ol/proj/Projection.js';
import View from 'ol/View.js';
import proj4 from 'proj4';
import {ScaleLine, defaults as defaultControls} from 'ol/control.js';
import {fromLonLat} from 'ol/proj.js';
import {register} from 'ol/proj/proj4.js';
// 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);
const projection = new Projection({
code: 'EPSG:21781',
extent: [485869.5728, 76443.1884, 837076.5648, 299941.7864],
});
const extent = [420000, 30000, 900000, 350000];
const layers = [
new ImageLayer({
extent: extent,
source: new ImageWMS({
url: 'https://wms.geo.admin.ch/',
crossOrigin: 'anonymous',
attributions:
'© <a href="https://shop.swisstopo.admin.ch/en/products/maps/national/lk1000"' +
'target="_blank">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="https://www.hydrodaten.admin.ch/en/notes-on-the-flood-alert-maps.html"' +
'target="_blank">Flood Alert / geo.admin.ch</a>',
params: {'LAYERS': 'ch.bafu.hydroweb-warnkarte_national'},
serverType: 'mapserver',
}),
}),
];
const 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,
}),
});
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Single Image WMS with Proj4js</title>
<link rel="stylesheet" href="node_modules/ol/ol.css">
<style>
.map {
width: 100%;
height: 400px;
}
</style>
</head>
<body>
<div id="map" class="map"></div>
<script type="module" src="main.js"></script>
</body>
</html>{
"name": "wms-image-custom-proj",
"dependencies": {
"ol": "10.3.1",
"proj4": "2.15.0"
},
"devDependencies": {
"vite": "^3.2.3"
},
"scripts": {
"start": "vite",
"build": "vite build"
}
}