243 lines
8.4 KiB
JavaScript
243 lines
8.4 KiB
JavaScript
// https://github.com/chrisveness/latlon-geohash/blob/master/latlon-geohash.js
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(() => {
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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/* Geohash encoding/decoding and associated functions (c) Chris Veness 2014-2016 / MIT Licence */
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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'use strict';
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/**
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* Geohash encode, decode, bounds, neighbours.
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*
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* @namespace
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*/
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var Geohash = {};
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/* (Geohash-specific) Base32 map */
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Geohash.base32 = '0123456789bcdefghjkmnpqrstuvwxyz';
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/**
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* Encodes latitude/longitude to geohash, either to specified precision or to automatically
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* evaluated precision.
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*
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* @param {number} lat - Latitude in degrees.
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* @param {number} lon - Longitude in degrees.
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* @param {number} [precision] - Number of characters in resulting geohash.
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* @returns {string} Geohash of supplied latitude/longitude.
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* @throws Invalid geohash.
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*
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* @example
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* var geohash = Geohash.encode(52.205, 0.119, 7); // geohash: 'u120fxw'
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*/
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exports.encode = Geohash.encode = function (lat, lon, precision) {
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// infer precision?
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if (typeof precision == 'undefined') {
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// refine geohash until it matches precision of supplied lat/lon
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for (var p = 1; p <= 12; p++) {
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var hash = Geohash.encode(lat, lon, p);
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var posn = Geohash.decode(hash);
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if (posn.lat == lat && posn.lon == lon) return hash;
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}
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precision = 12; // set to maximum
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}
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lat = Number(lat);
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lon = Number(lon);
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precision = Number(precision);
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if (isNaN(lat) || isNaN(lon) || isNaN(precision)) throw new Error('Invalid geohash');
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var idx = 0; // index into base32 map
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var bit = 0; // each char holds 5 bits
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var evenBit = true;
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var geohash = '';
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var latMin = -90, latMax = 90;
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var lonMin = -180, lonMax = 180;
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while (geohash.length < precision) {
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if (evenBit) {
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// bisect E-W longitude
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var lonMid = (lonMin + lonMax) / 2;
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if (lon >= lonMid) {
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idx = idx * 2 + 1;
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lonMin = lonMid;
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} else {
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idx = idx * 2;
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lonMax = lonMid;
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}
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} else {
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// bisect N-S latitude
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var latMid = (latMin + latMax) / 2;
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if (lat >= latMid) {
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idx = idx * 2 + 1;
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latMin = latMid;
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} else {
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idx = idx * 2;
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latMax = latMid;
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}
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}
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evenBit = !evenBit;
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if (++bit == 5) {
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// 5 bits gives us a character: append it and start over
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geohash += Geohash.base32.charAt(idx);
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bit = 0;
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idx = 0;
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}
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}
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return geohash;
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};
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/**
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* Decode geohash to latitude/longitude (location is approximate centre of geohash cell,
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* to reasonable precision).
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*
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* @param {string} geohash - Geohash string to be converted to latitude/longitude.
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* @returns {{lat:number, lon:number}} (Center of) geohashed location.
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* @throws Invalid geohash.
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*
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* @example
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* var latlon = Geohash.decode('u120fxw'); // latlon: { lat: 52.205, lon: 0.1188 }
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*/
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exports.decode = Geohash.decode = function (geohash) {
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var bounds = Geohash.bounds(geohash); // <-- the hard work
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// now just determine the centre of the cell...
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var latMin = bounds.sw.lat, lonMin = bounds.sw.lon;
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var latMax = bounds.ne.lat, lonMax = bounds.ne.lon;
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// cell centre
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var lat = (latMin + latMax) / 2;
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var lon = (lonMin + lonMax) / 2;
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// round to close to centre without excessive precision: ⌊2-log10(Δ°)⌋ decimal places
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lat = lat.toFixed(Math.floor(2 - Math.log(latMax - latMin) / Math.LN10));
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lon = lon.toFixed(Math.floor(2 - Math.log(lonMax - lonMin) / Math.LN10));
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return { lat: Number(lat), lon: Number(lon) };
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};
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/**
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* Returns SW/NE latitude/longitude bounds of specified geohash.
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*
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* @param {string} geohash - Cell that bounds are required of.
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* @returns {{sw: {lat: number, lon: number}, ne: {lat: number, lon: number}}}
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* @throws Invalid geohash.
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*/
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exports.bounds = Geohash.bounds = function (geohash) {
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if (geohash.length === 0) throw new Error('Invalid geohash');
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geohash = geohash.toLowerCase();
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var evenBit = true;
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var latMin = -90, latMax = 90;
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var lonMin = -180, lonMax = 180;
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for (var i = 0; i < geohash.length; i++) {
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var chr = geohash.charAt(i);
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var idx = Geohash.base32.indexOf(chr);
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if (idx == -1) throw new Error('Invalid geohash');
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for (var n = 4; n >= 0; n--) {
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var bitN = idx >> n & 1;
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if (evenBit) {
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// longitude
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var lonMid = (lonMin + lonMax) / 2;
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if (bitN == 1) {
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lonMin = lonMid;
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} else {
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lonMax = lonMid;
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}
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} else {
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// latitude
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var latMid = (latMin + latMax) / 2;
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if (bitN == 1) {
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latMin = latMid;
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} else {
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latMax = latMid;
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}
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}
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evenBit = !evenBit;
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}
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}
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var bounds = {
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sw: { lat: latMin, lon: lonMin },
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ne: { lat: latMax, lon: lonMax },
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};
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return bounds;
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};
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/**
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* Determines adjacent cell in given direction.
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*
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* @param geohash - Cell to which adjacent cell is required.
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* @param direction - Direction from geohash (N/S/E/W).
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* @returns {string} Geocode of adjacent cell.
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* @throws Invalid geohash.
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*/
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exports.adjacent = Geohash.adjacent = function (geohash, direction) {
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// based on github.com/davetroy/geohash-js
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geohash = geohash.toLowerCase();
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direction = direction.toLowerCase();
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if (geohash.length === 0) throw new Error('Invalid geohash');
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if ('nsew'.indexOf(direction) == -1) throw new Error('Invalid direction');
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var neighbour = {
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n: ['p0r21436x8zb9dcf5h7kjnmqesgutwvy', 'bc01fg45238967deuvhjyznpkmstqrwx'],
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s: ['14365h7k9dcfesgujnmqp0r2twvyx8zb', '238967debc01fg45kmstqrwxuvhjyznp'],
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e: ['bc01fg45238967deuvhjyznpkmstqrwx', 'p0r21436x8zb9dcf5h7kjnmqesgutwvy'],
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w: ['238967debc01fg45kmstqrwxuvhjyznp', '14365h7k9dcfesgujnmqp0r2twvyx8zb'],
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};
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var border = {
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n: ['prxz', 'bcfguvyz'],
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s: ['028b', '0145hjnp'],
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e: ['bcfguvyz', 'prxz'],
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w: ['0145hjnp', '028b'],
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};
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var lastCh = geohash.slice(-1); // last character of hash
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var parent = geohash.slice(0, -1); // hash without last character
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var type = geohash.length % 2;
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// check for edge-cases which don't share common prefix
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if (border[direction][type].indexOf(lastCh) != -1 && parent !== '') {
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parent = Geohash.adjacent(parent, direction);
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}
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// append letter for direction to parent
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return parent + Geohash.base32.charAt(neighbour[direction][type].indexOf(lastCh));
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};
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/**
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* Returns all 8 adjacent cells to specified geohash.
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*
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* @param {string} geohash - Geohash neighbours are required of.
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* @returns {{n,ne,e,se,s,sw,w,nw: string}}
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* @throws Invalid geohash.
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*/
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exports.neighbours = Geohash.neighbours = function (geohash) {
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return {
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'n': Geohash.adjacent(geohash, 'n'),
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'ne': Geohash.adjacent(Geohash.adjacent(geohash, 'n'), 'e'),
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'e': Geohash.adjacent(geohash, 'e'),
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'se': Geohash.adjacent(Geohash.adjacent(geohash, 's'), 'e'),
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's': Geohash.adjacent(geohash, 's'),
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'sw': Geohash.adjacent(Geohash.adjacent(geohash, 's'), 'w'),
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'w': Geohash.adjacent(geohash, 'w'),
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'nw': Geohash.adjacent(Geohash.adjacent(geohash, 'n'), 'w'),
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};
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};
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})(); |