88 lines
2.9 KiB
JavaScript
88 lines
2.9 KiB
JavaScript
import Map from '../src/ol/Map.js';
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import View from '../src/ol/View.js';
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import {getWidth, getCenter} from '../src/ol/extent.js';
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import {Image as ImageLayer, Tile as TileLayer} from '../src/ol/layer.js';
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import {fromLonLat, toLonLat} from '../src/ol/proj.js';
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import {ImageCanvas as ImageCanvasSource, Stamen} from '../src/ol/source.js';
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const map = new Map({
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layers: [
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new TileLayer({
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source: new Stamen({
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layer: 'watercolor'
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})
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})
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],
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target: 'map',
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view: new View({
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center: fromLonLat([-97, 38]),
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zoom: 4
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})
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});
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/**
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* Load the topojson data and create an ol/layer/Image for that data.
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*/
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d3.json('data/topojson/us.json', function(error, us) {
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const features = topojson.feature(us, us.objects.counties);
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/**
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* This function uses d3 to render the topojson features to a canvas.
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* @param {module:ol/extent~Extent} extent Extent.
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* @param {number} resolution Resolution.
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* @param {number} pixelRatio Pixel ratio.
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* @param {module:ol/size~Size} size Size.
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* @param {module:ol/proj/Projection~Projection} projection Projection.
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* @return {HTMLCanvasElement} A canvas element.
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*/
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const canvasFunction = function(extent, resolution, pixelRatio, size, projection) {
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const canvasWidth = size[0];
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const canvasHeight = size[1];
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const canvas = d3.select(document.createElement('canvas'));
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canvas.attr('width', canvasWidth).attr('height', canvasHeight);
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const context = canvas.node().getContext('2d');
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const d3Projection = d3.geoMercator().scale(1).translate([0, 0]);
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let d3Path = d3.geoPath().projection(d3Projection);
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const pixelBounds = d3Path.bounds(features);
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const pixelBoundsWidth = pixelBounds[1][0] - pixelBounds[0][0];
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const pixelBoundsHeight = pixelBounds[1][1] - pixelBounds[0][1];
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const geoBounds = d3.geoBounds(features);
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const geoBoundsLeftBottom = fromLonLat(geoBounds[0], projection);
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const geoBoundsRightTop = fromLonLat(geoBounds[1], projection);
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let geoBoundsWidth = geoBoundsRightTop[0] - geoBoundsLeftBottom[0];
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if (geoBoundsWidth < 0) {
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geoBoundsWidth += getWidth(projection.getExtent());
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}
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const geoBoundsHeight = geoBoundsRightTop[1] - geoBoundsLeftBottom[1];
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const widthResolution = geoBoundsWidth / pixelBoundsWidth;
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const heightResolution = geoBoundsHeight / pixelBoundsHeight;
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const r = Math.max(widthResolution, heightResolution);
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const scale = r / (resolution / pixelRatio);
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const center = toLonLat(getCenter(extent), projection);
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d3Projection.scale(scale).center(center)
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.translate([canvasWidth / 2, canvasHeight / 2]);
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d3Path = d3Path.projection(d3Projection).context(context);
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d3Path(features);
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context.stroke();
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return canvas.node();
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};
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const layer = new ImageLayer({
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source: new ImageCanvasSource({
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canvasFunction: canvasFunction,
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projection: 'EPSG:3857'
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})
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});
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map.addLayer(layer);
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});
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