Draw Shapes

Shape type:

Using the ol/interaction/Draw to create regular shapes

This demonstrates the use of the geometryFunction option for the ol/interaction/Draw. Select a shape type from the dropdown above to start drawing. To activate freehand drawing, hold the Shift key. Square drawing is achieved by using type: 'Circle' type with a geometryFunction that creates a 4-sided regular polygon instead of a circle. Box drawing uses type: 'Circle' with a geometryFunction that creates a box-shaped polygon instead of a circle. Star drawing uses a custom geometry function that converts a circle into a star using the center and radius provided by the draw interaction.

main.js

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

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

const source = new VectorSource({wrapX: false});

const vector = new VectorLayer({
  source: source,
});

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

const typeSelect = document.getElementById('type');

let draw; // global so we can remove it later
function addInteraction() {
  let value = typeSelect.value;
  if (value !== 'None') {
    let geometryFunction;
    if (value === 'Square') {
      value = 'Circle';
      geometryFunction = createRegularPolygon(4);
    } else if (value === 'Box') {
      value = 'Circle';
      geometryFunction = createBox();
    } else if (value === 'Star') {
      value = 'Circle';
      geometryFunction = function (coordinates, geometry) {
        const center = coordinates[0];
        const last = coordinates[coordinates.length - 1];
        const dx = center[0] - last[0];
        const dy = center[1] - last[1];
        const radius = Math.sqrt(dx * dx + dy * dy);
        const rotation = Math.atan2(dy, dx);
        const newCoordinates = [];
        const numPoints = 12;
        for (let i = 0; i < numPoints; ++i) {
          const angle = rotation + (i * 2 * Math.PI) / numPoints;
          const fraction = i % 2 === 0 ? 1 : 0.5;
          const offsetX = radius * fraction * Math.cos(angle);
          const offsetY = radius * fraction * Math.sin(angle);
          newCoordinates.push([center[0] + offsetX, center[1] + offsetY]);
        }
        newCoordinates.push(newCoordinates[0].slice());
        if (!geometry) {
          geometry = new Polygon([newCoordinates]);
        } else {
          geometry.setCoordinates([newCoordinates]);
        }
        return geometry;
      };
    }
    draw = new Draw({
      source: source,
      type: value,
      geometryFunction: geometryFunction,
    });
    map.addInteraction(draw);
  }
}

/**
 * Handle change event.
 */
typeSelect.onchange = function () {
  map.removeInteraction(draw);
  addInteraction();
};

document.getElementById('undo').addEventListener('click', function () {
  draw.removeLastPoint();
});

addInteraction();

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Draw Shapes</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css">
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div class="row">
      <div class="col-auto">
        <span class="input-group">
          <label class="input-group-text" for="type">Shape type:</label>
          <select class="form-select" id="type">
            <option value="Circle">Circle</option>
            <option value="Square">Square</option>
            <option value="Box">Box</option>
            <option value="Star">Star</option>
            <option value="None">None</option>
          </select>
          <input class="form-control" type="button" value="Undo" id="undo">
        </span>
      </div>
    </div>

    <script type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "draw-shapes",
  "dependencies": {
    "ol": "10.3.1"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}