Custom Polygon Styles

polygon 1 vector 69 style 22 GeometryFunction 1

Showing the vertices of a polygon with a custom style geometry.

In this example two different styles are created for the polygons:

The first style is for the polygons themselves.
The second style is to draw the vertices of the polygons.

main.js

import 'ol/ol.css';
import GeoJSON from 'ol/format/GeoJSON';
import Map from 'ol/Map';
import MultiPoint from 'ol/geom/MultiPoint';
import VectorLayer from 'ol/layer/Vector';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';
import {Circle as CircleStyle, Fill, Stroke, Style} from 'ol/style';

const styles = [
  /* We are using two different styles for the polygons:
   *  - The first style is for the polygons themselves.
   *  - The second style is to draw the vertices of the polygons.
   *    In a custom `geometry` function the vertices of a polygon are
   *    returned as `MultiPoint` geometry, which will be used to render
   *    the style.
   */
  new Style({
    stroke: new Stroke({
      color: 'blue',
      width: 3,
    }),
    fill: new Fill({
      color: 'rgba(0, 0, 255, 0.1)',
    }),
  }),
  new Style({
    image: new CircleStyle({
      radius: 5,
      fill: new Fill({
        color: 'orange',
      }),
    }),
    geometry: function (feature) {
      // return the coordinates of the first ring of the polygon
      const coordinates = feature.getGeometry().getCoordinates()[0];
      return new MultiPoint(coordinates);
    },
  }),
];

const geojsonObject = {
  'type': 'FeatureCollection',
  'crs': {
    'type': 'name',
    'properties': {
      'name': 'EPSG:3857',
    },
  },
  'features': [
    {
      'type': 'Feature',
      'geometry': {
        'type': 'Polygon',
        'coordinates': [
          [
            [-5e6, 6e6],
            [-5e6, 8e6],
            [-3e6, 8e6],
            [-3e6, 6e6],
            [-5e6, 6e6],
          ],
        ],
      },
    },
    {
      'type': 'Feature',
      'geometry': {
        'type': 'Polygon',
        'coordinates': [
          [
            [-2e6, 6e6],
            [-2e6, 8e6],
            [0, 8e6],
            [0, 6e6],
            [-2e6, 6e6],
          ],
        ],
      },
    },
    {
      'type': 'Feature',
      'geometry': {
        'type': 'Polygon',
        'coordinates': [
          [
            [1e6, 6e6],
            [1e6, 8e6],
            [3e6, 8e6],
            [3e6, 6e6],
            [1e6, 6e6],
          ],
        ],
      },
    },
    {
      'type': 'Feature',
      'geometry': {
        'type': 'Polygon',
        'coordinates': [
          [
            [-2e6, -1e6],
            [-1e6, 1e6],
            [0, -1e6],
            [-2e6, -1e6],
          ],
        ],
      },
    },
  ],
};

const source = new VectorSource({
  features: new GeoJSON().readFeatures(geojsonObject),
});

const layer = new VectorLayer({
  source: source,
  style: styles,
});

const map = new Map({
  layers: [layer],
  target: 'map',
  view: new View({
    center: [0, 3000000],
    zoom: 2,
  }),
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Custom Polygon Styles</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <!-- The lines below are 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,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "polygon-styles",
  "dependencies": {
    "ol": "6.13.1-dev"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}