d3 Integration

This example uses OpenLayers v4.0.1. The latest is v.

#### d3 Integration

Example of using OpenLayers and d3 together.

The example loads TopoJSON geometries and uses d3 (`d3.geo.path`) to render these geometries to a canvas element that is then used as the image of an OpenLayers image layer.

Related API documentation:

- ol.Map
,
- ol.View
,
- ol.extent
,
- ol.layer.Image
,
- ol.layer.Tile
,
- ol.proj
,
- ol.source.ImageCanvas
,
- ol.source.Stamen

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d3 Integration Example of using OpenLayers and d3 together. var map = new ol.Map({ layers: [ new ol.layer.Tile({ source: new ol.source.Stamen({ layer: 'watercolor' }) }) ], target: 'map', view: new ol.View({ center: ol.proj.fromLonLat([-97, 38]), zoom: 4 }) }); /** * Load the topojson data and create an ol.layer.Image for that data. */ d3.json('https://openlayers.org/en/v4.0.1/examples/data/topojson/us.json', function(error, us) { var features = topojson.feature(us, us.objects.counties); /** * This function uses d3 to render the topojson features to a canvas. * @param {ol.Extent} extent Extent. * @param {number} resolution Resolution. * @param {number} pixelRatio Pixel ratio. * @param {ol.Size} size Size. * @param {ol.proj.Projection} projection Projection. * @return {HTMLCanvasElement} A canvas element. */ var canvasFunction = function(extent, resolution, pixelRatio, size, projection) { var canvasWidth = size[0]; var canvasHeight = size[1]; var canvas = d3.select(document.createElement('canvas')); canvas.attr('width', canvasWidth).attr('height', canvasHeight); var context = canvas.node().getContext('2d'); var d3Projection = d3.geo.mercator().scale(1).translate([0, 0]); var d3Path = d3.geo.path().projection(d3Projection); var pixelBounds = d3Path.bounds(features); var pixelBoundsWidth = pixelBounds[1][0] - pixelBounds[0][0]; var pixelBoundsHeight = pixelBounds[1][1] - pixelBounds[0][1]; var geoBounds = d3.geo.bounds(features); var geoBoundsLeftBottom = ol.proj.transform( geoBounds[0], 'EPSG:4326', projection); var geoBoundsRightTop = ol.proj.transform( geoBounds[1], 'EPSG:4326', projection); var geoBoundsWidth = geoBoundsRightTop[0] - geoBoundsLeftBottom[0]; if (geoBoundsWidth < 0) { geoBoundsWidth += ol.extent.getWidth(projection.getExtent()); } var geoBoundsHeight = geoBoundsRightTop[1] - geoBoundsLeftBottom[1]; var widthResolution = geoBoundsWidth / pixelBoundsWidth; var heightResolution = geoBoundsHeight / pixelBoundsHeight; var r = Math.max(widthResolution, heightResolution); var scale = r / (resolution / pixelRatio); var center = ol.proj.transform(ol.extent.getCenter(extent), projection, 'EPSG:4326'); d3Projection.scale(scale).center(center) .translate([canvasWidth / 2, canvasHeight / 2]); d3Path = d3Path.projection(d3Projection).context(context); d3Path(features); context.stroke(); return canvas[0][0]; }; var layer = new ol.layer.Image({ source: new ol.source.ImageCanvas({ canvasFunction: canvasFunction, projection: 'EPSG:3857' }) }); map.addLayer(layer); }); <div id="map" class="map"></div>

    <!DOCTYPE html>
    <html>
      <head>
        <title>d3 Integration</title>
        <link rel="stylesheet" href="https://openlayers.org/en/v4.0.1/css/ol.css" type="text/css">
        <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
        <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
        <script src="https://openlayers.org/en/v4.0.1/build/ol.js"></script>
        <script src="https://d3js.org/d3.v3.min.js"></script>
        <script src="https://d3js.org/topojson.v1.min.js"></script>
      </head>
      <body>
        <div id="map" class="map"></div>
        <script>
          var map = new ol.Map({
            layers: [
              new ol.layer.Tile({
                source: new ol.source.Stamen({
                  layer: 'watercolor'
                })
              })
            ],
            target: 'map',
            view: new ol.View({
              center: ol.proj.fromLonLat([-97, 38]),
              zoom: 4
            })
          });

          /**
           * Load the topojson data and create an ol.layer.Image for that data.
           */
          d3.json('https://openlayers.org/en/v4.0.1/examples/data/topojson/us.json', function(error, us) {
            var features = topojson.feature(us, us.objects.counties);

            /**
             * This function uses d3 to render the topojson features to a canvas.
             * @param {ol.Extent} extent Extent.
             * @param {number} resolution Resolution.
             * @param {number} pixelRatio Pixel ratio.
             * @param {ol.Size} size Size.
             * @param {ol.proj.Projection} projection Projection.
             * @return {HTMLCanvasElement} A canvas element.
             */
            var canvasFunction = function(extent, resolution, pixelRatio,
                size, projection) {
              var canvasWidth = size[0];
              var canvasHeight = size[1];

              var canvas = d3.select(document.createElement('canvas'));
              canvas.attr('width', canvasWidth).attr('height', canvasHeight);

              var context = canvas.node().getContext('2d');

              var d3Projection = d3.geo.mercator().scale(1).translate([0, 0]);
              var d3Path = d3.geo.path().projection(d3Projection);

              var pixelBounds = d3Path.bounds(features);
              var pixelBoundsWidth = pixelBounds[1][0] - pixelBounds[0][0];
              var pixelBoundsHeight = pixelBounds[1][1] - pixelBounds[0][1];

              var geoBounds = d3.geo.bounds(features);
              var geoBoundsLeftBottom = ol.proj.transform(
                  geoBounds[0], 'EPSG:4326', projection);
              var geoBoundsRightTop = ol.proj.transform(
                  geoBounds[1], 'EPSG:4326', projection);
              var geoBoundsWidth = geoBoundsRightTop[0] - geoBoundsLeftBottom[0];
              if (geoBoundsWidth < 0) {
                geoBoundsWidth += ol.extent.getWidth(projection.getExtent());
              }
              var geoBoundsHeight = geoBoundsRightTop[1] - geoBoundsLeftBottom[1];

              var widthResolution = geoBoundsWidth / pixelBoundsWidth;
              var heightResolution = geoBoundsHeight / pixelBoundsHeight;
              var r = Math.max(widthResolution, heightResolution);
              var scale = r / (resolution / pixelRatio);

              var center = ol.proj.transform(ol.extent.getCenter(extent),
                  projection, 'EPSG:4326');
              d3Projection.scale(scale).center(center)
                  .translate([canvasWidth / 2, canvasHeight / 2]);
              d3Path = d3Path.projection(d3Projection).context(context);
              d3Path(features);
              context.stroke();

              return canvas[0][0];
            };

            var layer = new ol.layer.Image({
              source: new ol.source.ImageCanvas({
                canvasFunction: canvasFunction,
                projection: 'EPSG:3857'
              })
            });
            map.addLayer(layer);
          });
        </script>
      </body>
    </html>