Earthquakes with custom symbols

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var symbol = [[0, 0], [4, 2], [6, 0], [10, 5], [6, 3], [4, 5], [0, 0]];
var scale;
var scaleFunction = function(coordinate) {
  return [coordinate[0] * scale, coordinate[1] * scale];
};

var vector = new ol.layer.Vector({
  source: new ol.source.Vector({
    url: 'https://openlayers.org/en/v4.6.4/examples/data/kml/2012_Earthquakes_Mag5.kml',
    format: new ol.format.KML({
      extractStyles: false
    })
  }),
  style: styleFunction
});

var raster = new ol.layer.Tile({
  source: new ol.source.Stamen({
    layer: 'toner'
  })
});

var map = new ol.Map({
  layers: [raster, vector],
  target: 'map',
  view: new ol.View({
    center: [0, 0],
    zoom: 2
  })
});

<!DOCTYPE html>
<html>
  <head>
    <title>Earthquakes with custom symbols</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.6.4/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src=""></script>
    <script src="https://openlayers.org/en/v4.6.4/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script>
      var symbol = [[0, 0], [4, 2], [6, 0], [10, 5], [6, 3], [4, 5], [0, 0]];
      var scale;
      var scaleFunction = function(coordinate) {
        return [coordinate[0] * scale, coordinate[1] * scale];
      };

      var styleCache = {};
      var styleFunction = function(feature) {
        // 2012_Earthquakes_Mag5.kml stores the magnitude of each earthquake in a
        // standards-violating <magnitude> tag in each Placemark.  We extract it from
        // the Placemark's name instead.
        var name = feature.get('name');
        var magnitude = parseFloat(name.substr(2));
        var size = parseInt(10 + 40 * (magnitude - 5), 10);
        scale = size / 10;
        var style = styleCache[size];
        if (!style) {
          var canvas =
              /** @type {HTMLCanvasElement} */ (document.createElement('canvas'));
          var vectorContext = ol.render.toContext(
              /** @type {CanvasRenderingContext2D} */ (canvas.getContext('2d')),
              {size: [size, size], pixelRatio: 1});
          vectorContext.setStyle(new ol.style.Style({
            fill: new ol.style.Fill({color: 'rgba(255, 153, 0, 0.4)'}),
            stroke: new ol.style.Stroke({color: 'rgba(255, 204, 0, 0.2)', width: 2})
          }));
          vectorContext.drawGeometry(new ol.geom.Polygon([symbol.map(scaleFunction)]));
          style = new ol.style.Style({
            image: new ol.style.Icon({
              img: canvas,
              imgSize: [size, size],
              rotation: 1.2
            })
          });
          styleCache[size] = style;
        }
        return style;
      };

      var vector = new ol.layer.Vector({
        source: new ol.source.Vector({
          url: 'https://openlayers.org/en/v4.6.4/examples/data/kml/2012_Earthquakes_Mag5.kml',
          format: new ol.format.KML({
            extractStyles: false
          })
        }),
        style: styleFunction
      });

      var raster = new ol.layer.Tile({
        source: new ol.source.Stamen({
          layer: 'toner'
        })
      });

      var map = new ol.Map({
        layers: [raster, vector],
        target: 'map',
        view: new ol.View({
          center: [0, 0],
          zoom: 2
        })
      });
    </script>
  </body>
</html>