LineString Arrows

Example of drawing arrows for each line string segment.

Example of drawing arrows for each line string segment.

<!DOCTYPE html>
<html>
  <head>
    <title>LineString Arrows</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="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <script src="https://openlayers.org/en/v4.6.4/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script>
      var raster = new ol.layer.Tile({
        source: new ol.source.OSM()
      });

      var source = new ol.source.Vector();

      var styleFunction = function(feature) {
        var geometry = feature.getGeometry();
        var styles = [
          // linestring
          new ol.style.Style({
            stroke: new ol.style.Stroke({
              color: '#ffcc33',
              width: 2
            })
          })
        ];

        geometry.forEachSegment(function(start, end) {
          var dx = end[0] - start[0];
          var dy = end[1] - start[1];
          var rotation = Math.atan2(dy, dx);
          // arrows
          styles.push(new ol.style.Style({
            geometry: new ol.geom.Point(end),
            image: new ol.style.Icon({
              src: 'https://openlayers.org/en/v4.6.4/examples/data/arrow.png',
              anchor: [0.75, 0.5],
              rotateWithView: true,
              rotation: -rotation
            })
          }));
        });

        return styles;
      };
      var vector = new ol.layer.Vector({
        source: source,
        style: styleFunction
      });

      var map = new ol.Map({
        layers: [raster, vector],
        target: 'map',
        view: new ol.View({
          center: [-11000000, 4600000],
          zoom: 4
        })
      });

      map.addInteraction(new ol.interaction.Draw({
        source: source,
        type: 'LineString'
      }));
    </script>
  </body>
</html>