vector-tile-esm/src/geojson.js

Parses vector tiles

import { classifyRings } from "./rings.js";

export const types = ["Unknown", "Point", "LineString", "Polygon"];

export function toGeoJSON(size, sx = 0, sy = 0) {
  // Input size is the side length of the (square) area over which the
  //  coordinate space of this tile [0, this.extent] will be rendered.
  // Input sx, sy is the origin (top left corner) of the output coordinates
  //  within the (size x size) rendered area of the full tile.

  size = size || this.extent;
  const scale = size / this.extent;
  let coords = this.loadGeometry();
  let type = types[this.type];

  function project(line) {
    return line.map(p => [p.x * scale - sx, p.y * scale - sy]);
  }

  switch (type) {
    case "Point":
      coords = project( coords.map(p => p[0]) );
      break;

    case "LineString":
      coords = coords.map(project);
      break;

    case "Polygon":
      coords = classifyRings(coords);
      coords = coords.map(polygon => polygon.map(project));
      break;
  }

  if (coords.length === 1) {
    coords = coords[0];
  } else {
    type = "Multi" + type;
  }

  const result = {
    type: "Feature",
    geometry: {
      type: type,
      coordinates: coords
    },
    properties: this.properties
  };

  if ("id" in this) result.id = this.id;

  return result;
}