geojson-bounding-box/index.js

Efficiently computes a GeoJSON's bounding box.

/**
 * @description Create input GeoJSON bounding box.
 * @param {GeoJSON} geojson Input GeoJSON.
 * @return {Array} GeoJSON bounding box.
 */
module.exports = function(geojson) {
  const bbox = [
    Number.POSITIVE_INFINITY,
    Number.POSITIVE_INFINITY,
    Number.POSITIVE_INFINITY,
    Number.NEGATIVE_INFINITY,
    Number.NEGATIVE_INFINITY,
    Number.NEGATIVE_INFINITY,
  ];

  // Update bbox with each coordinate
  let dimensions = 2;
  for (const coordinate of coordEach(geojson)) {
    dimensions = Math.max(dimensions, coordinate.length);
    for (let i = 0; i < coordinate.length; ++i) {
      const j = 3 + i;
      bbox[i] = Math.min(bbox[i], coordinate[i]);
      bbox[j] = Math.max(bbox[j], coordinate[i]);
    }
  }

  // Remove 3rd dimension if not present in data.
  if (dimensions !== 3) {
    return [bbox[0], bbox[1], bbox[3], bbox[4]];
  }
  return bbox;
};

/**
 * @description Generator that yields each GeoJSON coordinate.
 * @param {GeoJSON} geojson Input GeoJSON.
 * @yields [Array] GeoJSON 2D or 3D coordinate.
 */
function* coordEach(geojson) {
  switch (geojson.type) {
    case 'Point':
      yield geojson.coordinates;
      break;
    case 'LineString':
    case 'MultiPoint':
      yield* geojson.coordinates;
      break;
    case 'Polygon':
    case 'MultiLineString':
      for (const part of geojson.coordinates) {
        yield* part;
      }
      break;
    case 'MultiPolygon':
      for (const polygon of geojson.coordinates) {
        for (const ring of polygon) {
          yield* ring;
        }
      }
      break;
    case 'GeometryCollection':
      for (const geometry of geojson.geometries) {
        yield* coordEach(geometry);
      }
      break;
    case 'FeatureCollection':
      for (const feature of geojson.features) {
        yield* coordEach(feature);
      }
      break;
    default:
      yield* coordEach(geojson.geometry);
  }
}