ol-ext
Version:
A set of cool extensions for OpenLayers (ol) in node modules structure
203 lines (176 loc) • 6.58 kB
JavaScript
/** Geohash encoding/decoding and associated functions
* (c) Chris Veness 2014-2019 / MIT Licence
* https://github.com/chrisveness/latlon-geohash
*/
var ol_geohash = {
// (geohash-specific) Base32 map
base32: '0123456789bcdefghjkmnpqrstuvwxyz'
};
/** Encodes latitude/longitude to geohash, either to specified precision or to automatically
* evaluated precision.
* @param {ol.coordinate} lonlat Longitude, Latitude in degrees.
* @param {number} [precision] Number of characters in resulting geohash.
* @returns {string} Geohash of supplied latitude/longitude.
*/
var ol_geohash_fromLonLat = function(lonlat, precision) {
var lon = lonlat[0];
var lat = lonlat[1];
// infer precision?
if (!precision) {
// refine geohash until it matches precision of supplied lat/lon
for (var p=1; p<=12; p++) {
var hash = ol_geohash_fromLonLat([lon, lat], p);
var posn = ol_geohash_toLonLat(hash);
if (posn.lat==lat && posn.lon==lon) return hash;
}
precision = 12; // set to maximum
}
if (precision < 1 || precision > 12) precision = 12;
var idx = 0; // index into base32 map
var bit = 0; // each char holds 5 bits
var evenBit = true;
var geohash = '';
var latMin = -90, latMax = 90;
var lonMin = -180, lonMax = 180;
while (geohash.length < precision) {
if (evenBit) {
// bisect E-W longitude
var lonMid = (lonMin + lonMax) / 2;
if (lon >= lonMid) {
idx = idx*2 + 1;
lonMin = lonMid;
} else {
idx = idx*2;
lonMax = lonMid;
}
} else {
// bisect N-S latitude
var latMid = (latMin + latMax) / 2;
if (lat >= latMid) {
idx = idx*2 + 1;
latMin = latMid;
} else {
idx = idx*2;
latMax = latMid;
}
}
evenBit = !evenBit;
if (++bit == 5) {
// 5 bits gives us a character: append it and start over
geohash += ol_geohash.base32.charAt(idx);
bit = 0;
idx = 0;
}
}
return geohash;
};
/** Decode geohash to latitude/longitude
* (location is approximate centre of geohash cell, to reasonable precision).
* @param {string} geohash - Geohash string to be converted to latitude/longitude.
* @returns {ol.coordinate}
*/
var ol_geohash_toLonLat = function(geohash) {
var extent = ol_geohash_getExtent(geohash); // <-- the hard work
// now just determine the centre of the cell...
var latMin = extent[1], lonMin = extent[0];
var latMax = extent[3], lonMax = extent[2];
// cell centre
var lat = (latMin + latMax)/2;
var lon = (lonMin + lonMax)/2;
// round to close to centre without excessive precision: ⌊2-log10(Δ°)⌋ decimal places
lat = lat.toFixed(Math.floor(2-Math.log(latMax-latMin)/Math.LN10));
lon = lon.toFixed(Math.floor(2-Math.log(lonMax-lonMin)/Math.LN10));
return [Number(lon), Number(lat)];
};
/** Returns SW/NE latitude/longitude bounds of specified geohash.
* @param {string} geohash Cell that bounds are required of.
* @returns {ol.extent | false}
*/
var ol_geohash_getExtent = function(geohash) {
if (!geohash) return false;
geohash = geohash.toLowerCase();
var evenBit = true;
var latMin = -90, latMax = 90;
var lonMin = -180, lonMax = 180;
for (var i=0; i<geohash.length; i++) {
var chr = geohash.charAt(i);
var idx = ol_geohash.base32.indexOf(chr);
if (idx == -1) return false;
for (var n=4; n>=0; n--) {
var bitN = idx >> n & 1;
if (evenBit) {
// longitude
var lonMid = (lonMin+lonMax) / 2;
if (bitN == 1) {
lonMin = lonMid;
} else {
lonMax = lonMid;
}
} else {
// latitude
var latMid = (latMin+latMax) / 2;
if (bitN == 1) {
latMin = latMid;
} else {
latMax = latMid;
}
}
evenBit = !evenBit;
}
}
return [lonMin, latMin, lonMax, latMax];
};
/** Determines adjacent cell in given direction.
* @param {string} geohash Geohash cel
* @param {string} direction direction as char : N/S/E/W.
* @returns {string|false}
*/
var ol_geohash_getAdjacent = function (geohash, direction) {
// based on github.com/davetroy/geohash-js
geohash = geohash.toLowerCase();
direction = direction.toLowerCase();
if (!geohash) return false;
if ('nsew'.indexOf(direction) == -1) return false;
const neighbour = {
n: [ 'p0r21436x8zb9dcf5h7kjnmqesgutwvy', 'bc01fg45238967deuvhjyznpkmstqrwx' ],
s: [ '14365h7k9dcfesgujnmqp0r2twvyx8zb', '238967debc01fg45kmstqrwxuvhjyznp' ],
e: [ 'bc01fg45238967deuvhjyznpkmstqrwx', 'p0r21436x8zb9dcf5h7kjnmqesgutwvy' ],
w: [ '238967debc01fg45kmstqrwxuvhjyznp', '14365h7k9dcfesgujnmqp0r2twvyx8zb' ],
};
const border = {
n: [ 'prxz', 'bcfguvyz' ],
s: [ '028b', '0145hjnp' ],
e: [ 'bcfguvyz', 'prxz' ],
w: [ '0145hjnp', '028b' ],
};
const lastCh = geohash.slice(-1); // last character of hash
let parent = geohash.slice(0, -1); // hash without last character
const type = geohash.length % 2;
// check for edge-cases which don't share common prefix
if (border[direction][type].indexOf(lastCh) != -1 && parent != '') {
parent = ol_geohash_getAdjacent(parent, direction);
}
// append letter for direction to parent
return parent + ol_geohash.base32.charAt(neighbour[direction][type].indexOf(lastCh));
}
/** Returns all 8 adjacent cells to specified geohash.
* @param {string} geohash Geohash neighbours are required of.
* @returns {{n,ne,e,se,s,sw,w,nw: string}}
*/
var ol_geohash_getNeighbours = function(geohash) {
return {
'n': ol_geohash_getAdjacent(geohash, 'n'),
'ne': ol_geohash_getAdjacent(ol_geohash_getAdjacent(geohash, 'n'), 'e'),
'e': ol_geohash_getAdjacent(geohash, 'e'),
'se': ol_geohash_getAdjacent(ol_geohash_getAdjacent(geohash, 's'), 'e'),
's': ol_geohash_getAdjacent(geohash, 's'),
'sw': ol_geohash_getAdjacent(ol_geohash_getAdjacent(geohash, 's'), 'w'),
'w': ol_geohash_getAdjacent(geohash, 'w'),
'nw': ol_geohash_getAdjacent(ol_geohash_getAdjacent(geohash, 'n'), 'w'),
};
}
export {ol_geohash_fromLonLat as fromLonLat}
export {ol_geohash_toLonLat as toLonLat}
export {ol_geohash_getExtent as getExtent}
export {ol_geohash_getAdjacent as getAdjacent}
export {ol_geohash_getNeighbours as getNeighbours}