geojson-vt integration

main.js

import 'ol/ol.css';
import GeoJSON from 'ol/format/GeoJSON';
import Map from 'ol/Map';
import OSM from 'ol/source/OSM';
import Projection from 'ol/proj/Projection';
import VectorTileSource from 'ol/source/VectorTile';
import View from 'ol/View';
import {
  Tile as TileLayer,
  VectorTile as VectorTileLayer,
} from 'ol/layer';

// Converts geojson-vt data to GeoJSON
const replacer = function (key, value) {
  if (value.geometry) {
    let type;
    const rawType = value.type;
    let geometry = value.geometry;

    if (rawType === 1) {
      type = 'MultiPoint';
      if (geometry.length == 1) {
        type = 'Point';
        geometry = geometry[0];
      }
    } else if (rawType === 2) {
      type = 'MultiLineString';
      if (geometry.length == 1) {
        type = 'LineString';
        geometry = geometry[0];
      }
    } else if (rawType === 3) {
      type = 'Polygon';
      if (geometry.length > 1) {
        type = 'MultiPolygon';
        geometry = [geometry];
      }
    }

    return {
      'type': 'Feature',
      'geometry': {
        'type': type,
        'coordinates': geometry,
      },
      'properties': value.tags,
    };
  } else {
    return value;
  }
};

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

const url = 'data/geojson/countries.geojson';
fetch(url)
  .then(function (response) {
    return response.json();
  })
  .then(function (json) {
    const tileIndex = geojsonvt(json, {
      extent: 4096,
      debug: 1,
    });
    const format = new GeoJSON({
      // Data returned from geojson-vt is in tile pixel units
      dataProjection: new Projection({
        code: 'TILE_PIXELS',
        units: 'tile-pixels',
        extent: [0, 0, 4096, 4096],
      }),
    });
    const vectorSource = new VectorTileSource({
      tileUrlFunction: function (tileCoord) {
        // Use the tile coordinate as a pseudo URL for caching purposes
        return JSON.stringify(tileCoord);
      },
      tileLoadFunction: function (tile, url) {
        const tileCoord = JSON.parse(url);
        const data = tileIndex.getTile(
          tileCoord[0],
          tileCoord[1],
          tileCoord[2]
        );
        const geojson = JSON.stringify(
          {
            type: 'FeatureCollection',
            features: data ? data.features : [],
          },
          replacer
        );
        const features = format.readFeatures(geojson, {
          extent: vectorSource.getTileGrid().getTileCoordExtent(tileCoord),
          featureProjection: map.getView().getProjection(),
        });
        tile.setFeatures(features);
      },
    });
    const vectorLayer = new VectorTileLayer({
      source: vectorSource,
    });
    map.addLayer(vectorLayer);
  });

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>geojson-vt integration</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>
    <script src="https://mapbox.github.io/geojson-vt/geojson-vt-dev.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="main.js"></script>
  </body>
</html>

geojson-vt integration

main.js

index.html

package.json