@googlemaps/google-maps-services-js/src/util.ts

Node.js client library for Google Maps API Web Services

/**
 * Copyright 2020 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { LatLngLiteral } from "./common";

/**
 * Polyline encodes an array of LatLng objects.
 *
 * See {@link https://developers.google.com/maps/documentation/utilities/polylinealgorithm}
 *
 */
export function encodePath(path: LatLngLiteral[]): string {
  const result: string[] = [];
  let start: [number, number] = [0, 0];
  let end: [number, number];

  const encodePart = function (part: number) {
    part = part < 0 ? ~(part << 1) : part << 1;
    while (part >= 0x20) {
      result.push(String.fromCharCode((0x20 | (part & 0x1f)) + 63));
      part >>= 5;
    }
    result.push(String.fromCharCode(part + 63));
  };

  for (let i = 0, I = path.length || 0; i < I; ++i) {
    end = [Math.round(path[i].lat * 1e5), Math.round(path[i].lng * 1e5)];
    encodePart(end[0] - start[0]); // lat
    encodePart(end[1] - start[1]); // lng
    start = end;
  }

  return result.join("");
}

/**
 * Decodes a polyline encoded string.
 *
 * See {@link https://developers.google.com/maps/documentation/utilities/polylinealgorithm}
 */
export function decodePath(encodedPath: string): LatLngLiteral[] {
  const len: number = encodedPath.length || 0;
  const path = new Array(Math.floor(encodedPath.length / 2));
  let index: number = 0;
  let lat: number = 0;
  let lng: number = 0;
  let pointIndex: number;

  for (pointIndex = 0; index < len; ++pointIndex) {
    let result: number = 1;
    let shift: number = 0;
    let b: number;
    do {
      b = encodedPath.charCodeAt(index++) - 63 - 1;
      result += b << shift;
      shift += 5;
    } while (b >= 0x1f);
    lat += result & 1 ? ~(result >> 1) : result >> 1;

    result = 1;
    shift = 0;
    do {
      b = encodedPath.charCodeAt(index++) - 63 - 1;
      result += b << shift;
      shift += 5;
    } while (b >= 0x1f);
    lng += result & 1 ? ~(result >> 1) : result >> 1;

    path[pointIndex] = { lat: lat * 1e-5, lng: lng * 1e-5 };
  }
  path.length = pointIndex;

  return path;
}