Smoothing lines using Chaikins algorithm

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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.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Smoothing lines using Chaikins algorithm</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>
    <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="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 {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {OSM, Vector as VectorSource} from 'ol/source';
import Draw from 'ol/interaction/Draw';

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);
});

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package.json{
  "name": "chaikin",
  "dependencies": {
    "ol": "6.1.1",
    "chaikin-smooth": "^1.0.4"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}