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| 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 | 1x 1x 1x 1x 14x 14x 14x 14x 14x 14x 14x 14x 14x 14x 1x | /** ****************************************************************************************************
* File: getBBoxStartingPoint.js
* Project: geohash
* @author Nick Soggin <iSkore@users.noreply.github.com> on 19-Feb-2019
*******************************************************************************************************/
'use strict';
const
decode = require( './decode' ),
encode = require( './encode' ),
geohashToBBox = require( './geohashToBBox' ),
{ ENCODE_AUTO } = require( './variables' );
/**
* getBBoxStartingPoint
*
* Beginning operations for generating a geohash bbox.
* Get the geohash for the southwest corner of a bbox and how many hash steps there are to the northeast corner.
*
* @param {number} minLng - minimum longitude
* @param {number} minLat - minimum latitude
* @param {number} maxLng - maximum longitude
* @param {number} maxLat - maximum latitude
* @param {number} [precision=ENCODE_AUTO] - geohash precision
* @returns {{hashSouthWest: string, lngStep: number, latStep: number}}
* southwest hash and how many lng/lat steps to the northeast hash
*/
function getBBoxStartingPoint( minLng, minLat, maxLng, maxLat, precision = ENCODE_AUTO ) {
const
hashSouthWest = encode( minLng, minLat, precision ),
hashNorthEast = encode( maxLng, maxLat, precision ),
latLng = decode( hashSouthWest, true ),
perLng = latLng.error.lng * 2,
perLat = latLng.error.lat * 2,
boxSouthWest = geohashToBBox( hashSouthWest ),
boxNorthEast = geohashToBBox( hashNorthEast ),
lngStep = Math.round( ( boxNorthEast[ 0 ] - boxSouthWest[ 0 ] ) / perLng ),
latStep = Math.round( ( boxNorthEast[ 1 ] - boxSouthWest[ 1 ] ) / perLat );
return {
latStep,
lngStep,
hashSouthWest
};
}
module.exports = getBBoxStartingPoint;
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