Earthquake Clusters

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 and ol.style.Style#geometry.

KML, vector, style, geometry, cluster
<!DOCTYPE html>
<html>
<head>
<title>Earthquake Clusters</title>
<script src="https://code.jquery.com/jquery-1.11.2.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="http://openlayers.org/en/v3.9.0/css/ol.css" type="text/css">
<script src="http://openlayers.org/en/v3.9.0/build/ol.js"></script>

<style>
#map {
  position: relative;
}
#info {
  position: absolute;
  height: 1px;
  width: 1px;
  z-index: 100;
}
.tooltip.in {
  opacity: 1;
  filter: alpha(opacity=100);
}
.tooltip.top .tooltip-arrow {
  border-top-color: white;
}
.tooltip-inner {
  border: 2px solid white;
}

</style>
</head>
<body>
<div class="container-fluid">

<div class="row-fluid">
  <div class="span12">
    <div id="map" class="map"></div>
  </div>
</div>

</div>
<script>
var earthquakeFill = new ol.style.Fill({
  color: 'rgba(255, 153, 0, 0.8)'
});
var earthquakeStroke = new ol.style.Stroke({
  color: 'rgba(255, 204, 0, 0.2)',
  width: 1
});
var textFill = new ol.style.Fill({
  color: '#fff'
});
var textStroke = new ol.style.Stroke({
  color: 'rgba(0, 0, 0, 0.6)',
  width: 3
});
var invisibleFill = new ol.style.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 ol.style.Style({
    geometry: feature.getGeometry(),
    image: new ol.style.RegularShape({
      radius1: radius,
      radius2: 3,
      points: 5,
      angle: Math.PI,
      fill: earthquakeFill,
      stroke: earthquakeStroke
    })
  });
}

var maxFeatureCount;
function calculateClusterInfo(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 = ol.extent.createEmpty();
    for (var j = 0, jj = originalFeatures.length; j < jj; ++j) {
      ol.extent.extend(extent, originalFeatures[j].getGeometry().getExtent());
    }
    maxFeatureCount = Math.max(maxFeatureCount, jj);
    radius = 0.25 * (ol.extent.getWidth(extent) + ol.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 ol.style.Style({
      image: new ol.style.Circle({
        radius: feature.get('radius'),
        fill: new ol.style.Fill({
          color: [255, 153, 0, Math.min(0.8, 0.4 + (size / maxFeatureCount))]
        })
      }),
      text: new ol.style.Text({
        text: size.toString(),
        fill: textFill,
        stroke: textStroke
      })
    })];
  } else {
    var originalFeature = feature.get('features')[0];
    style = [createEarthquakeStyle(originalFeature)];
  }
  return style;
}

function selectStyleFunction(feature, resolution) {
  var styles = [new ol.style.Style({
    image: new ol.style.Circle({
      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;
}

var vector = new ol.layer.Vector({
  source: new ol.source.Cluster({
    distance: 40,
    source: new ol.source.Vector({
      url: '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],
  interactions: ol.interaction.defaults().extend([new ol.interaction.Select({
    condition: function(evt) {
      return evt.originalEvent.type == 'mousemove' ||
          evt.type == 'singleclick';
    },
    style: selectStyleFunction
  })]),
  target: 'map',
  view: new ol.View({
    center: [0, 0],
    zoom: 2
  })
});

</script>
</body>
</html>