Press n or j to go to the next uncovered block, b, p or k for the previous block.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 | 1x 1x 44x 44x 44x 44x 1x 43x 1x 42x 1x 41x 41x 41x 41x 41x 41x 41x 41x 41x 41x 41x 1175x 602x 602x 276x 276x 326x 326x 573x 573x 309x 309x 264x 264x 1175x 1175x 235x 235x 235x 41x 1x | /** ****************************************************************************************************
* File: encode.js
* Project: geohash
* @author Nick Soggin <iSkore@users.noreply.github.com> on 19-Feb-2019
*******************************************************************************************************/
'use strict';
const
{
BASE32,
ENCODE_AUTO,
MIN_LNG,
MIN_LAT,
MAX_LNG,
MAX_LAT
} = require( './variables' );
const
{
determinePrecision,
isNumber
} = require( './utils' );
/**
* encode
* Encodes latitude/longitude to geohash, either to specified precision or to automatically
* evaluated precision.
*
* @param {number} lng - Longitude in degrees.
* @param {number} lat - Latitude in degrees.
* @param {number} [precision=ENCODE_AUTO] - Number of characters in resulting geohash.
* @returns {string} Geohash of supplied latitude/longitude.
* @throws Invalid geohash.
*
* @example
* const geohash = Geohash.encode(52.205, 0.119, 7); // geohash: 'u120fxw'
*/
function encode( lng, lat, precision = ENCODE_AUTO ) {
lng = +lng;
lat = +lat;
precision = +precision;
if ( !isNumber( lng ) ) {
throw new Error( 'Invalid value for `lng`' );
}
else if ( !isNumber( lat ) ) {
throw new Error( 'Invalid value for `lat`' );
}
else if ( !isNumber( precision ) ) {
throw new Error( 'Invalid value for `precision`' );
}
precision = determinePrecision( lng, lat, precision );
let
geohash = '',
hash = 0, // index into BASE32 map
bit = 0, // each char holds 5 bits
evenBit = true,
lngMin = MIN_LNG,
latMin = MIN_LAT,
lngMax = MAX_LNG,
latMax = MAX_LAT,
mid = 0;
while ( geohash.length < precision ) {
if ( evenBit ) {
// bisect E-W longitude
mid = ( lngMin + lngMax ) / 2;
if ( lng >= mid ) {
hash = ( hash << 1 ) + 1;
lngMin = mid;
}
else {
hash = hash << 1;
lngMax = mid;
}
}
else {
// bisect N-S latitude
mid = ( latMin + latMax ) / 2;
if ( lat >= mid ) {
hash = ( hash << 1 ) + 1;
latMin = mid;
}
else {
hash = hash << 1;
latMax = mid;
}
}
evenBit = !evenBit;
if ( ++bit === 5 ) {
// 5 bits gives us a character: append it and start over
geohash += BASE32[ hash ];
bit = 0;
hash = 0;
}
}
return geohash;
}
module.exports = encode;
|