Method _parseTileBuffer

modules/services/VectorTileService.js:316–437

* _parseTileBuffer * @param source * @param tile * @param buffer

(source, tile, buffer)

   * @param  buffer
   */
  _parseTileBuffer(source, tile, buffer) {
    if (!buffer) return;  // 'no data' is ok

    // Get some info about this tile and its neighbors
    const [x, y, z] = tile.xyz;
    const tileID = tile.id;
    const tileExtent = tile.wgs84Extent;

    //       -y
    //     +----+
    //  -x |    | +x
    //     +----+
    //       +y

    // Define tile edges (lower x,y,z - higher x,y,z)
    const leftEdge = `${x-1},${y},${z}-${tileID}`;
    const rightEdge = `${tileID}-${x+1},${y},${z}`;
    const topEdge = `${x},${y-1},${z}-${tileID}`;
    const bottomEdge = `${tileID}-${x},${y+1},${z}`;

    const vt = new VectorTile(new Protobuf(buffer));
    const cache = this._getZoomCache(source, z);

    const newFeatures = [];
    for (const [layerID, vtLayer] of Object.entries(vt.layers)) {
      if (!vtLayer) continue;

      // Determine extent of tile coordinates
      const min = 0;
      const max = vtLayer.extent;  // default 4096

      // For each feature on the vector tile...
      for (let i = 0; i < vtLayer.length; i++) {
        const vtFeature = vtLayer.feature(i);
        const [left, top, right, bottom] = vtFeature.bbox();

        // This feature is wholly on a neighbor tile - it just spills onto this tile in the buffer..
        if (left > max || top > max || right < min || bottom < min) continue;

        // Force all properties to strings
        for (const [k, v] of Object.entries(vtFeature.properties)) {
          vtFeature.properties[k] = v.toString();
        }

        // When features have the same properties, we'll consider them mergeable.
        const prophash = utilHashcode(stringify(vtFeature.properties)).toString();

        // If the feature doesn't have an id, use the prophash as the id
        if (!vtFeature.id) {
          vtFeature.id = prophash;
        }

        // Convert to GeoJSON
        const orig = vtFeature.toGeoJSON(x, y, z);

        // It's common for a vector tile to return 'Multi' GeoJSON features..
        // e.g. All the roads together in one `MultiLineString`.
        // For our purposes, we really want to work with them as single features..