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Smoothing lines using Chaikins algorithm

smooth1 smoothing1 chaikin1


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.

main.js
import 'ol/ol.css';
import Draw from 'ol/interaction/Draw';
import Map from 'ol/Map';
import View from 'ol/View';
import {OSM, Vector as VectorSource} from 'ol/source';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';

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;
}

const vectorSource = new VectorSource({});

const map = new Map({
  layers: [
    new TileLayer({
      source: new OSM(),
      opacity: 0.5,
    }),
    new VectorLayer({
      source: vectorSource,
    }),
  ],
  target: 'map',
  view: new View({
    center: [1078373.595, 6871994.591],
    zoom: 5,
  }),
});

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

const draw = new Draw({
  source: vectorSource,
  type: 'LineString',
});
map.addInteraction(draw);
draw.on('drawend', function (event) {
  if (!shallSmoothen.checked) {
    return;
  }
  const feat = event.feature;
  const geometry = feat.getGeometry();
  const coords = geometry.getCoordinates();
  const smoothened = makeSmooth(coords, parseInt(numIterations.value, 10) || 5);
  geometry.setCoordinates(smoothened);
});
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Smoothing lines using Chaikins algorithm</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep"></script>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,URL,TextDecoder,Number.isInteger"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </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 src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "chaikin",
  "dependencies": {
    "ol": "6.9.0",
    "chaikin-smooth": "^1.0.4"
  },
  "devDependencies": {
    "parcel": "^2.0.0-beta.1"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}