vector-tile-esm/src/vectortilelayer.js

Parses vector tiles

import { VectorTileFeature } from "./vectortilefeature.js";

export function VectorTileLayer(pbf, end) {
  // Public
  this.version = 1;
  this.name = null;
  this.extent = 4096;
  this.length = 0;

  // Private
  this._pbf = pbf;
  this._keys = [];
  this._values = [];
  this._features = [];

  pbf.readFields(readLayer, this, end);

  this.length = this._features.length;
}

function readLayer(tag, layer, pbf) {
  if (tag === 15) layer.version = pbf.readVarint();
  else if (tag === 1) layer.name = pbf.readString();
  else if (tag === 5) layer.extent = pbf.readVarint();
  else if (tag === 2) layer._features.push(pbf.pos);
  else if (tag === 3) layer._keys.push(pbf.readString());
  else if (tag === 4) layer._values.push(readValueMessage(pbf));
}

function readValueMessage(pbf) {
  let value = null;
  const end = pbf.readVarint() + pbf.pos;

  while (pbf.pos < end) {
    const tag = pbf.readVarint() >> 3;

    value = tag === 1 ? pbf.readString() :
      tag === 2 ? pbf.readFloat() :
      tag === 3 ? pbf.readDouble() :
      tag === 4 ? pbf.readVarint64() :
      tag === 5 ? pbf.readVarint() :
      tag === 6 ? pbf.readSVarint() :
      tag === 7 ? pbf.readBoolean() : null;
  }

  return value;
}

// return feature 'i' from this layer as a 'VectorTileFeature'
VectorTileLayer.prototype.feature = function(i) {
  const { _features, extent, _pbf, _keys, _values } = this;

  const lastFeature = _features.length - 1;
  if (i < 0 || i > lastFeature) throw Error("feature index out of bounds");

  _pbf.pos = _features[i];

  const end = _pbf.readVarint() + _pbf.pos;
  return new VectorTileFeature(_pbf, end, extent, _keys, _values);
};

VectorTileLayer.prototype.toGeoJSON = function(size, sx, sy) {
  const features = Array.from(Array(this._features.length), (v, i) => {
    return this.feature(i).toGeoJSON(size, sx, sy);
  });

  return { type: "FeatureCollection", features, extent: this.extent };
};