Example of a WMS GetLegendGraphic.
WMS supports the getLegendGraphic request. This example demonstrates the use of the getLegendUrl
method.
As a legend can be responsive to the scale it is updated on every change of the resolution.
import 'ol/ol.css';
import ImageWMS from 'ol/source/ImageWMS';
import Map from 'ol/Map';
import OSM from 'ol/source/OSM';
import View from 'ol/View';
import {Image as ImageLayer, Tile as TileLayer} from 'ol/layer';
const wmsSource = new ImageWMS({
url: 'https://ahocevar.com/geoserver/wms',
params: {'LAYERS': 'topp:states'},
ratio: 1,
serverType: 'geoserver',
});
const updateLegend = function (resolution) {
const graphicUrl = wmsSource.getLegendUrl(resolution);
const img = document.getElementById('legend');
img.src = graphicUrl;
};
const layers = [
new TileLayer({
source: new OSM(),
}),
new ImageLayer({
extent: [-13884991, 2870341, -7455066, 6338219],
source: wmsSource,
}),
];
const map = new Map({
layers: layers,
target: 'map',
view: new View({
center: [-10997148, 4569099],
zoom: 4,
}),
});
// Initial legend
const resolution = map.getView().getResolution();
updateLegend(resolution);
// Update the legend when the resolution changes
map.getView().on('change:resolution', function (event) {
const resolution = event.target.getResolution();
updateLegend(resolution);
});
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>WMS GetLegendGraphic</title>
<!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
<script src="https://unpkg.com/elm-pep"></script>
<!-- The line below is 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,URL,TextDecoder,Number.isInteger"></script>
<style>
.map {
width: 100%;
height:400px;
}
</style>
</head>
<body>
<div id="map" class="map"></div>
Legend:
<div><img id="legend"/></div>
<script src="main.js"></script>
</body>
</html>
{
"name": "wms-getlegendgraphic",
"dependencies": {
"ol": "6.6.1"
},
"devDependencies": {
"parcel": "^2.0.0-beta.1"
},
"scripts": {
"start": "parcel index.html",
"build": "parcel build --public-url . index.html"
}
}