// geohash.js
// Geohash library for Javascript
// (c) 2008 David Troy
// Distributed under the MIT License
// Original at: https://github.com/davetroy/geohash-js
// Modified by Irrelon Software Limited (http://www.irrelon.com)
// to clean up and modularise the code using Node.js-style exports
// and add a few helper methods.
// @by Rob Evans - rob@irrelon.com
"use strict";
/*
Define some shared constants that will be used by all instances
of the module.
*/
var bits,
base32,
neighbors,
borders,
PI180 = Math.PI / 180,
PI180R = 180 / Math.PI,
earthRadius = 6371; // mean radius of the earth
bits = [16, 8, 4, 2, 1];
base32 = "0123456789bcdefghjkmnpqrstuvwxyz";
neighbors = {
right: {even: "bc01fg45238967deuvhjyznpkmstqrwx"},
left: {even: "238967debc01fg45kmstqrwxuvhjyznp"},
top: {even: "p0r21436x8zb9dcf5h7kjnmqesgutwvy"},
bottom: {even: "14365h7k9dcfesgujnmqp0r2twvyx8zb"}
};
borders = {
right: {even: "bcfguvyz"},
left: {even: "0145hjnp"},
top: {even: "prxz"},
bottom: {even: "028b"}
};
neighbors.bottom.odd = neighbors.left.even;
neighbors.top.odd = neighbors.right.even;
neighbors.left.odd = neighbors.bottom.even;
neighbors.right.odd = neighbors.top.even;
borders.bottom.odd = borders.left.even;
borders.top.odd = borders.right.even;
borders.left.odd = borders.bottom.even;
borders.right.odd = borders.top.even;
var GeoHash = function () {};
/**
* Converts degrees to radians.
* @param {Number} degrees
* @return {Number} radians
*/
GeoHash.prototype.radians = function radians (degrees) {
return degrees * PI180;
};
/**
* Converts radians to degrees.
* @param {Number} radians
* @return {Number} degrees
*/
GeoHash.prototype.degrees = function (radians) {
return radians * PI180R;
};
GeoHash.prototype.refineInterval = function (interval, cd, mask) {
if (cd & mask) { //jshint ignore: line
interval[0] = (interval[0] + interval[1]) / 2;
} else {
interval[1] = (interval[0] + interval[1]) / 2;
}
};
/**
* Calculates all surrounding neighbours of a hash and returns them.
* @param {String} centerHash The hash at the center of the grid.
* @param options
* @returns {*}
*/
GeoHash.prototype.calculateNeighbours = function (centerHash, options) {
var response;
if (!options || options.type === 'object') {
response = {
center: centerHash,
left: this.calculateAdjacent(centerHash, 'left'),
right: this.calculateAdjacent(centerHash, 'right'),
top: this.calculateAdjacent(centerHash, 'top'),
bottom: this.calculateAdjacent(centerHash, 'bottom')
};
response.topLeft = this.calculateAdjacent(response.left, 'top');
response.topRight = this.calculateAdjacent(response.right, 'top');
response.bottomLeft = this.calculateAdjacent(response.left, 'bottom');
response.bottomRight = this.calculateAdjacent(response.right, 'bottom');
} else {
response = [];
response[4] = centerHash;
response[3] = this.calculateAdjacent(centerHash, 'left');
response[5] = this.calculateAdjacent(centerHash, 'right');
response[1] = this.calculateAdjacent(centerHash, 'top');
response[7] = this.calculateAdjacent(centerHash, 'bottom');
response[0] = this.calculateAdjacent(response[3], 'top');
response[2] = this.calculateAdjacent(response[5], 'top');
response[6] = this.calculateAdjacent(response[3], 'bottom');
response[8] = this.calculateAdjacent(response[5], 'bottom');
}
return response;
};
/**
* Calculates a new lat/lng by travelling from the center point in the
* bearing specified for the distance specified.
* @param {Array} centerPoint An array with latitude at index 0 and
* longitude at index 1.
* @param {Number} distanceKm The distance to travel in kilometers.
* @param {Number} bearing The bearing to travel in degrees (zero is
* north).
* @returns {{lat: Number, lng: Number}}
*/
GeoHash.prototype.calculateLatLngByDistanceBearing = function (centerPoint, distanceKm, bearing) {
var curLon = centerPoint[1],
curLat = centerPoint[0],
destLat = Math.asin(Math.sin(this.radians(curLat)) * Math.cos(distanceKm / earthRadius) + Math.cos(this.radians(curLat)) * Math.sin(distanceKm / earthRadius) * Math.cos(this.radians(bearing))),
tmpLon = this.radians(curLon) + Math.atan2(Math.sin(this.radians(bearing)) * Math.sin(distanceKm / earthRadius) * Math.cos(this.radians(curLat)), Math.cos(distanceKm / earthRadius) - Math.sin(this.radians(curLat)) * Math.sin(destLat)),
destLon = (tmpLon + 3 * Math.PI) % (2 * Math.PI) - Math.PI; // normalise to -180..+180ยบ
return {
lat: this.degrees(destLat),
lng: this.degrees(destLon)
};
};
/**
* Calculates the extents of a bounding box around the center point which
* encompasses the radius in kilometers passed.
* @param {Array} centerPoint An array with latitude at index 0 and
* longitude at index 1.
* @param radiusKm Radius in kilometers.
* @returns {{lat: Array, lng: Array}}
*/
GeoHash.prototype.calculateExtentByRadius = function (centerPoint, radiusKm) {
var maxWest,
maxEast,
maxNorth,
maxSouth,
lat = [],
lng = [];
maxNorth = this.calculateLatLngByDistanceBearing(centerPoint, radiusKm, 0);
maxEast = this.calculateLatLngByDistanceBearing(centerPoint, radiusKm, 90);
maxSouth = this.calculateLatLngByDistanceBearing(centerPoint, radiusKm, 180);
maxWest = this.calculateLatLngByDistanceBearing(centerPoint, radiusKm, 270);
lat[0] = maxNorth.lat;
lat[1] = maxSouth.lat;
lng[0] = maxWest.lng;
lng[1] = maxEast.lng;
return {
lat: lat,
lng: lng
};
};
/**
* Calculates all the geohashes that make up the bounding box that surrounds
* the circle created from the center point and radius passed.
* @param {Array} centerPoint An array with latitude at index 0 and
* longitude at index 1.
* @param {Number} radiusKm The radius in kilometers to encompass.
* @param {Number} precision The number of characters to limit the returned
* geohash strings to.
* @returns {Array} The array of geohashes that encompass the bounding box.
*/
GeoHash.prototype.calculateHashArrayByRadius = function (centerPoint, radiusKm, precision) {
var extent = this.calculateExtentByRadius(centerPoint, radiusKm),
northWest = [extent.lat[0], extent.lng[0]],
northEast = [extent.lat[0], extent.lng[1]],
southWest = [extent.lat[1], extent.lng[0]],
northWestHash = this.encode(northWest[0], northWest[1], precision),
northEastHash = this.encode(northEast[0], northEast[1], precision),
southWestHash = this.encode(southWest[0], southWest[1], precision),
hash,
widthCount = 0,
heightCount = 0,
widthIndex,
heightIndex,
hashArray = [];
hash = northWestHash;
hashArray.push(hash);
// Walk from north west to north east until we find the north east geohash
while (hash !== northEastHash) {
hash = this.calculateAdjacent(hash, 'right');
widthCount++;
hashArray.push(hash);
}
hash = northWestHash;
// Walk from north west to south west until we find the south west geohash
while (hash !== southWestHash) {
hash = this.calculateAdjacent(hash, 'bottom');
heightCount++;
}
// We now know the width and height in hash boxes of the area, fill in the
// rest of the hashes into the hashArray array
for (widthIndex = 0; widthIndex <= widthCount; widthIndex++) {
hash = hashArray[widthIndex];
for (heightIndex = 0; heightIndex < heightCount; heightIndex++) {
hash = this.calculateAdjacent(hash, 'bottom');
hashArray.push(hash);
}
}
return hashArray;
};
/**
* Calculates an adjacent hash to the hash passed, in the direction
* specified.
* @param {String} srcHash The hash to calculate adjacent to.
* @param {String} dir Either "top", "left", "bottom" or "right".
* @returns {String} The resulting geohash.
*/
GeoHash.prototype.calculateAdjacent = function (srcHash, dir) {
srcHash = srcHash.toLowerCase();
var lastChr = srcHash.charAt(srcHash.length - 1),
type = (srcHash.length % 2) ? 'odd' : 'even',
base = srcHash.substring(0, srcHash.length - 1);
if (borders[dir][type].indexOf(lastChr) !== -1) {
base = this.calculateAdjacent(base, dir);
}
return base + base32[neighbors[dir][type].indexOf(lastChr)];
};
/**
* Decodes a string geohash back to a longitude/latitude array.
* The array contains three latitudes and three longitudes. The
* first of each is the lower extent of the geohash bounding box,
* the second is the upper extent and the third is the center
* of the geohash bounding box.
* @param {String} geohash The hash to decode.
* @returns {Object}
*/
GeoHash.prototype.decode = function (geohash) {
var isEven = 1,
lat = [],
lon = [],
i, c, cd, j, mask,
latErr,
lonErr;
lat[0] = -90.0;
lat[1] = 90.0;
lon[0] = -180.0;
lon[1] = 180.0;
latErr = 90.0;
lonErr = 180.0;
for (i = 0; i < geohash.length; i++) {
c = geohash[i];
cd = base32.indexOf(c);
for (j = 0; j < 5; j++) {
mask = bits[j];
if (isEven) {
lonErr /= 2;
this.refineInterval(lon, cd, mask);
} else {
latErr /= 2;
this.refineInterval(lat, cd, mask);
}
isEven = !isEven;
}
}
lat[2] = (lat[0] + lat[1]) / 2;
lon[2] = (lon[0] + lon[1]) / 2;
return {
lat: lat,
lng: lon
};
};
/**
* Encodes a longitude/latitude to geohash string.
* @param latitude
* @param longitude
* @param {Number=} precision Length of the geohash string. Defaults to 12.
* @returns {String}
*/
GeoHash.prototype.encode = function (latitude, longitude, precision) {
var isEven = 1,
mid,
lat = [],
lon = [],
bit = 0,
ch = 0,
geoHash = "";
if (!precision) { precision = 12; }
lat[0] = -90.0;
lat[1] = 90.0;
lon[0] = -180.0;
lon[1] = 180.0;
while (geoHash.length < precision) {
if (isEven) {
mid = (lon[0] + lon[1]) / 2;
if (longitude > mid) {
ch |= bits[bit]; //jshint ignore: line
lon[0] = mid;
} else {
lon[1] = mid;
}
} else {
mid = (lat[0] + lat[1]) / 2;
if (latitude > mid) {
ch |= bits[bit]; //jshint ignore: line
lat[0] = mid;
} else {
lat[1] = mid;
}
}
isEven = !isEven;
if (bit < 4) {
bit++;
} else {
geoHash += base32[ch];
bit = 0;
ch = 0;
}
}
return geoHash;
};
if (typeof module !== 'undefined') { module.exports = GeoHash; }