Edit

geojson-vt integration

mapbox5 vector71 tiles6 geojson9

Slice GeoJSON into vector tiles on the fly in the browser.

Example of integration with geojson-vt library.

main.js
import GeoJSON from 'ol/format/GeoJSON';
import Map from 'ol/Map';
import Projection from 'ol/proj/Projection';
import VectorTileLayer from 'ol/layer/VectorTile';
import VectorTileSource from 'ol/source/VectorTile';
import View from 'ol/View';
import {Fill, Style} from 'ol/style';

// Converts geojson-vt data to GeoJSON
const replacer = function (key, value) {
  if (!value || !value.geometry) {
    return value;
  }

  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,
  };
};

const style = new Style({
  fill: new Fill({
    color: '#eeeeee',
  }),
});

const layer = new VectorTileLayer({
  background: '#1a2b39',
  style: function (feature) {
    const color = feature.get('COLOR') || '#eeeeee';
    style.getFill().setColor(color);
    return style;
  },
});

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

const url = 'https://openlayers.org/data/vector/ecoregions.json';
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);
      },
    });
    layer.setSource(vectorSource);
  });
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>geojson-vt integration</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/[email protected]/dist/elm-pep.js"></script>
    <script src="https://mapbox.github.io/geojson-vt/geojson-vt-dev.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "geojson-vt",
  "dependencies": {
    "ol": "7.0.0"
  },
  "devDependencies": {
    "vite": "^3.0.3",
    "@babel/core": "latest"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}