Example of using OpenLayers and d3 together.
The example loads TopoJSON geometries and uses d3 (d3.geo.path
) to render these geometries to a SVG element.
import 'ol/ol.css';
import Map from 'ol/Map';
import SourceState from 'ol/source/State';
import Stamen from 'ol/source/Stamen';
import View from 'ol/View';
import {Layer, Tile as TileLayer} from 'ol/layer';
import {fromLonLat, toLonLat} from 'ol/proj';
import {getCenter, getWidth} from 'ol/extent';
class CanvasLayer extends Layer {
constructor(options) {
super(options);
this.features = options.features;
this.svg = d3
.select(document.createElement('div'))
.append('svg')
.style('position', 'absolute');
this.svg.append('path').datum(this.features).attr('class', 'boundary');
}
getSourceState() {
return SourceState.READY;
}
render(frameState) {
const width = frameState.size[0];
const height = frameState.size[1];
const projection = frameState.viewState.projection;
const d3Projection = d3.geoMercator().scale(1).translate([0, 0]);
let d3Path = d3.geoPath().projection(d3Projection);
const pixelBounds = d3Path.bounds(this.features);
const pixelBoundsWidth = pixelBounds[1][0] - pixelBounds[0][0];
const pixelBoundsHeight = pixelBounds[1][1] - pixelBounds[0][1];
const geoBounds = d3.geoBounds(this.features);
const geoBoundsLeftBottom = fromLonLat(geoBounds[0], projection);
const geoBoundsRightTop = fromLonLat(geoBounds[1], projection);
let geoBoundsWidth = geoBoundsRightTop[0] - geoBoundsLeftBottom[0];
if (geoBoundsWidth < 0) {
geoBoundsWidth += getWidth(projection.getExtent());
}
const geoBoundsHeight = geoBoundsRightTop[1] - geoBoundsLeftBottom[1];
const widthResolution = geoBoundsWidth / pixelBoundsWidth;
const heightResolution = geoBoundsHeight / pixelBoundsHeight;
const r = Math.max(widthResolution, heightResolution);
const scale = r / frameState.viewState.resolution;
const center = toLonLat(getCenter(frameState.extent), projection);
const angle = (-frameState.viewState.rotation * 180) / Math.PI;
d3Projection
.scale(scale)
.center(center)
.translate([width / 2, height / 2])
.angle(angle);
d3Path = d3Path.projection(d3Projection);
d3Path(this.features);
this.svg.attr('width', width);
this.svg.attr('height', height);
this.svg.select('path').attr('d', d3Path);
return this.svg.node();
}
}
const map = new Map({
layers: [
new TileLayer({
source: new Stamen({
layer: 'watercolor',
}),
}),
],
target: 'map',
view: new View({
center: fromLonLat([-97, 38]),
zoom: 4,
}),
});
/**
* Load the topojson data and create an ol/layer/Image for that data.
*/
d3.json('data/topojson/us.json').then(function (us) {
const layer = new CanvasLayer({
features: topojson.feature(us, us.objects.counties),
});
map.addLayer(layer);
});
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>d3 Integration</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>
<script src="https://unpkg.com/d3@6.7.0/dist/d3.min.js"></script>
<script src="https://unpkg.com/topojson@3.0.2/dist/topojson.js"></script>
<style>
.map {
width: 100%;
height:400px;
}
path.boundary {
fill: none;
stroke: #777;
}
</style>
</head>
<body>
<div id="map" class="map"></div>
<script src="main.js"></script>
</body>
</html>
{
"name": "d3",
"dependencies": {
"ol": "6.6.1"
},
"devDependencies": {
"parcel": "^2.0.0-beta.1"
},
"scripts": {
"start": "parcel index.html",
"build": "parcel build --public-url . index.html"
}
}