ydn.geohash

YDN GEO module. geohash

This module provides encoding and decoding two dimensional geometric coordinates into string hash while preserving locality of the data points. This is essentially a form of Z-order curve representation of two dimensions.

See Wikipedia Geohash article for more detail.

Static Methods
decode(hash) Dencode geohash into a 2D coordinate.
Parameters:
{string} hash
Standard geohash string representation.
Return:
{!Array.number}
Return four elements array representing [latitude, longitude, error_latitude, error_longitude].
encode(coordinate) Encode a 2D coordinate into geohash.

Encode a pair of latitude and longitude into standard geohash. Geohash string uses 32 lower case char of 0123456789bcdefghjkmnpqrstuvwxyz.

Latitude range from -90 to 90.

Longitude range from -180 to -180.

Precision is positive integer number of resulting hash string. Each char in hash string encode 4 bits of latitude and longitude pair. Hence, error is 1 / Math.pow(2, 4 * precision/2) * 180. For default precision of 12 char, the error is ±0.0000107288 or ±1.190 meters in equator.

var h = ydn.geohash.encode([37.8324, 112.5584]);
var cor = ydn.geohash.dencode(h);
Parameters:
{!Array.number} coordinate
A coordinate pair with optional precision given as array of [latitude, longitude, opt_precision]. Default value of opt_precision is 12.
Return:
{string}
Geohash representation of given coordinate.
neighbor(hash, dir) Return neighbor geohash of given position.

Unit rectangular vector have two elements representing the first one for longitude or EAST-WEST and the second one for latitude or NORTH-SOUTH.

{
  NORTH: [1, 0],
  NORTH_EAST: [1, 1],
  NORTH_WEST: [1, -1],
  EAST: [0, 1],
  SOUTH: [-1, 0],
  SOUTH_EAST: [0, 1],
  SOUTH_WEST: [-1, -1],
  WEST: [0, -1]
};
Parameters:
{string} hash
Given position.
{!Array.number} dir
Unit rectangular vector representation direction.
Return:
{string}
Neighbor geohash.