Smoothing lines using Chaikins algorithm


This uses Chaikins algorithm to smooth drawn lines.

This example uses the npm package chaikin-smooth which implements Chaikins algorithm to smooth drawn lines. Start by drawing on the map. Once you finish a drawing, the feature's geometry will be smoothed as configured via the form elements.

<!DOCTYPE html>
<html>
  <head>
    <title>Smoothing lines using Chaikins algorithm</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v5.3.0/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>

  </head>
  <body>
    <div id="map" class="map"></div>
    <form class="form-inline">
      <label for="shall-smoothen">Smooth drawn geometry?</label>
      <input id="shall-smoothen" type="checkbox" checked><br>
      <label for="iterations">Number of smoothings</label>
      <input style="width: 250px;" type="range" id="iterations" min="2" max="10" step="1" value="5">
    </form>
    <script>
      import Map from 'ol/Map.js';
      import View from 'ol/View.js';
      import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';
      import {OSM, Vector as VectorSource} from 'ol/source.js';
      import Draw from 'ol/interaction/Draw.js';

      import smooth from 'chaikin-smooth';

      function makeSmooth(path, numIterations) {
        numIterations = Math.min(Math.max(numIterations, 1), 10);
        while (numIterations > 0) {
          path = smooth(path);
          numIterations--;
        }
        return path;
      }

      var vectorSource = new VectorSource({});

      var map = new Map({
        layers: [
          new TileLayer({
            source: new OSM(),
            opacity: 0.5
          }),
          new VectorLayer({
            source: vectorSource
          })
        ],
        target: 'map',
        view: new View({
          center: [1078373.5950, 6871994.5910],
          zoom: 5
        })
      });

      var shallSmoothen = document.getElementById('shall-smoothen');
      var numIterations = document.getElementById('iterations');

      var draw = new Draw({
        source: vectorSource,
        type: 'LineString'
      });
      map.addInteraction(draw);
      draw.on('drawend', function(event) {
        if (!shallSmoothen.checked) {
          return;
        }
        var feat = event.feature;
        var geometry = feat.getGeometry();
        var coords = geometry.getCoordinates();
        var smoothened = makeSmooth(coords, parseInt(numIterations.value, 10) || 5);
        geometry.setCoordinates(smoothened);
      });
    </script>
  </body>
</html>