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geohash - Copy.js
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geohash - Copy.js
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// geohash.js
// Geohash library for Javascript
// (c) 2008 David Troy
// Distributed under the MIT License
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;
function refine_interval(interval, cd, mask) {
if (cd&mask)
interval[0] = (interval[0] + interval[1])/2;
else
interval[1] = (interval[0] + interval[1])/2;
}
function calculateAdjacent(srcHash, dir) {
srcHash = srcHash.toLowerCase();
var lastChr = srcHash.charAt(srcHash.length-1);
var type = (srcHash.length % 2) ? 'odd' : 'even';
var base = srcHash.substring(0,srcHash.length-1);
if (BORDERS[dir][type].indexOf(lastChr)!=-1)
base = calculateAdjacent(base, dir);
return base + BASE32[NEIGHBORS[dir][type].indexOf(lastChr)];
}
function decodeGeoHash(geohash) {
var is_even = 1;
var lat = []; var lon = [];
lat[0] = -90.0; lat[1] = 90.0;
lon[0] = -180.0; lon[1] = 180.0;
lat_err = 90.0; lon_err = 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 (is_even) {
lon_err /= 2;
refine_interval(lon, cd, mask);
} else {
lat_err /= 2;
refine_interval(lat, cd, mask);
}
is_even = !is_even;
}
}
lat[2] = (lat[0] + lat[1])/2;
lon[2] = (lon[0] + lon[1])/2;
return { latitude: lat, longitude: lon};
}
function encodeGeoHash(latitude, longitude) {
var is_even=1;
var i=0;
var lat = []; var lon = [];
var bit=0;
var ch=0;
var precision = 12;
geohash = "";
lat[0] = -90.0; lat[1] = 90.0;
lon[0] = -180.0; lon[1] = 180.0;
while (geohash.length < precision) {
if (is_even) {
mid = (lon[0] + lon[1]) / 2;
if (longitude > mid) {
ch |= BITS[bit];
lon[0] = mid;
} else
lon[1] = mid;
} else {
mid = (lat[0] + lat[1]) / 2;
if (latitude > mid) {
ch |= BITS[bit];
lat[0] = mid;
} else
lat[1] = mid;
}
is_even = !is_even;
if (bit < 4)
bit++;
else {
geohash += BASE32[ch];
bit = 0;
ch = 0;
}
}
return geohash;
}