LineString Arrows

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LineString Arrows

Example of drawing arrows for each line string segment.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>LineString Arrows</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=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>

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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import Point from 'ol/geom/Point';
import Draw from 'ol/interaction/Draw';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {OSM, Vector as VectorSource} from 'ol/source';
import {Icon, Stroke, Style} from 'ol/style';

var raster = new TileLayer({
  source: new OSM()
});

var source = new VectorSource();

var styleFunction = function(feature) {
  var geometry = feature.getGeometry();
  var styles = [
    // linestring
    new Style({
      stroke: new 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 Style({
      geometry: new Point(end),
      image: new Icon({
        src: 'data/arrow.png',
        anchor: [0.75, 0.5],
        rotateWithView: true,
        rotation: -rotation
      })
    }));
  });

  return styles;
};
var vector = new VectorLayer({
  source: source,
  style: styleFunction
});

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

map.addInteraction(new Draw({
  source: source,
  type: 'LineString'
}));

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package.json{
  "name": "line-arrows",
  "dependencies": {
    "ol": "6.1.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}