turf-isolines

Takes a FeatureCollection of points with z values and an array of value breaks and generates isolines. These are commonly used to create elevation maps, but can be used for general data interpolation as well.

<!doctype html>
<html lang="en">
  <head>
    <link rel="stylesheet" href="https://rawcdn.githack.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
    <link rel="stylesheet" href="assets/css/styles.css" type="text/css">
    <script src="//cdn.jsdelivr.net/npm/@turf/turf@5/turf.min.js"></script>
    <script src="https://rawcdn.githack.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js" type="text/javascript"></script>
    <script src="assets/js/es6-promise.min.js"></script>
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL,fetch"></script>
    <script src="assets/js/helpers.js"></script>
    <title>Turf and OpenLayers 3 - Isolines</title>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script type="text/javascript">

      // Declare a source and directly embed the GeoJSON using the
      // "experimental parameter "object"
      var vectorSource = new ol.source.Vector();

      // Declare a vector layer with the already
      // created source containing added features
      var vectorLayer = new ol.layer.Vector({
        source: vectorSource
      });

      // Instanciate a map and add layers
      var map = new ol.Map({
        target: 'map',
        layers: [
          new ol.layer.Tile({
            source: new ol.source.OSM()
          }),
          vectorLayer
        ],
        view: new ol.View({
          center: ol.proj.fromLonLat([4.52475, 45.47611]),
          zoom: 7
        })
      });

      fetch('assets/data/france_meteo.geojson').then(function(response) {
        return response.json().then(function(points_fc) {
          var breaks = [
            990, 992, 994, 996, 998,
            1000, 1002, 1004, 1006, 1008,
            1010, 1012, 1014, 1016, 1018,
            1020, 1022, 1024, 1026, 1028,
            1030, 1032
          ];

          var isolines = turf.isolines(points_fc, 'pressure', 100, breaks);
          vectorSource.addFeatures(geojsonToFeatures(isolines, {
            featureProjection: 'EPSG:3857'
          }));
        });
      });
    </script>
  </body>
</html>

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