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Earthquake Clusters

KML vector style geometry cluster

Demonstrates the use of style geometries to render source features of a cluster.

This example parses a KML file and renders the features as clusters on a vector layer. The styling in this example is quite involved. Single earthquake locations (rendered as stars) have a size relative to their magnitude. Clusters have an opacity relative to the number of features in the cluster, and a size that represents the extent of the features that make up the cluster. When clicking or hovering on a cluster, the individual features that make up the cluster will be shown.

To achieve this, we make heavy use of style functions.

index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Earthquake Clusters</title>
    <!-- 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=fetch,requestAnimationFrame,Element.prototype.classList,URL"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="index.js"></script>
  </body>
</html>
index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import {createEmpty, getWidth, getHeight, extend} from 'ol/extent';
import KML from 'ol/format/KML';
import {defaults as defaultInteractions, Select} from 'ol/interaction';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {Cluster, Stamen, Vector as VectorSource} from 'ol/source';
import {Circle as CircleStyle, Fill, RegularShape, Stroke, Style, Text} from 'ol/style';


var earthquakeFill = new Fill({
  color: 'rgba(255, 153, 0, 0.8)'
});
var earthquakeStroke = new Stroke({
  color: 'rgba(255, 204, 0, 0.2)',
  width: 1
});
var textFill = new Fill({
  color: '#fff'
});
var textStroke = new Stroke({
  color: 'rgba(0, 0, 0, 0.6)',
  width: 3
});
var invisibleFill = new Fill({
  color: 'rgba(255, 255, 255, 0.01)'
});

function createEarthquakeStyle(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 radius = 5 + 20 * (magnitude - 5);

  return new Style({
    geometry: feature.getGeometry(),
    image: new RegularShape({
      radius1: radius,
      radius2: 3,
      points: 5,
      angle: Math.PI,
      fill: earthquakeFill,
      stroke: earthquakeStroke
    })
  });
}

var maxFeatureCount;
var vector = null;
var calculateClusterInfo = function(resolution) {
  maxFeatureCount = 0;
  var features = vector.getSource().getFeatures();
  var feature, radius;
  for (var i = features.length - 1; i >= 0; --i) {
    feature = features[i];
    var originalFeatures = feature.get('features');
    var extent = createEmpty();
    var j = (void 0), jj = (void 0);
    for (j = 0, jj = originalFeatures.length; j < jj; ++j) {
      extend(extent, originalFeatures[j].getGeometry().getExtent());
    }
    maxFeatureCount = Math.max(maxFeatureCount, jj);
    radius = 0.25 * (getWidth(extent) + getHeight(extent)) /
        resolution;
    feature.set('radius', radius);
  }
};

var currentResolution;
function styleFunction(feature, resolution) {
  if (resolution != currentResolution) {
    calculateClusterInfo(resolution);
    currentResolution = resolution;
  }
  var style;
  var size = feature.get('features').length;
  if (size > 1) {
    style = new Style({
      image: new CircleStyle({
        radius: feature.get('radius'),
        fill: new Fill({
          color: [255, 153, 0, Math.min(0.8, 0.4 + (size / maxFeatureCount))]
        })
      }),
      text: new Text({
        text: size.toString(),
        fill: textFill,
        stroke: textStroke
      })
    });
  } else {
    var originalFeature = feature.get('features')[0];
    style = createEarthquakeStyle(originalFeature);
  }
  return style;
}

function selectStyleFunction(feature) {
  var styles = [new Style({
    image: new CircleStyle({
      radius: feature.get('radius'),
      fill: invisibleFill
    })
  })];
  var originalFeatures = feature.get('features');
  var originalFeature;
  for (var i = originalFeatures.length - 1; i >= 0; --i) {
    originalFeature = originalFeatures[i];
    styles.push(createEarthquakeStyle(originalFeature));
  }
  return styles;
}

vector = new VectorLayer({
  source: new Cluster({
    distance: 40,
    source: new VectorSource({
      url: 'data/kml/2012_Earthquakes_Mag5.kml',
      format: new KML({
        extractStyles: false
      })
    })
  }),
  style: styleFunction
});

var raster = new TileLayer({
  source: new Stamen({
    layer: 'toner'
  })
});

var map = new Map({
  layers: [raster, vector],
  interactions: defaultInteractions().extend([new Select({
    condition: function(evt) {
      return evt.type == 'pointermove' ||
          evt.type == 'singleclick';
    },
    style: selectStyleFunction
  })]),
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2
  })
});
package.json{
  "name": "earthquake-clusters",
  "dependencies": {
    "ol": "6.2.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}