Tool to decode / encode coordinates with Geohash, a geographic data representation system used on to shorten url on geohash.org

Geohash - dCode

Tag(s) : Geography

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Geohash is the name of an algorithm, created in 2008 and deposited in the public domain, which transforms a pair (latitude, longitude) of GPS coordinates into a code of letters and numbers. This algorithm is based on a recursive division of space into grids.

The geohash algorithm uses a variant of base32 with these 32 characters `0123456789bcdefghjkmnpqrstuvwxyz`. The geohash can therefore be treated as a value in base 32, convertible into binary.

__Example:__ `dc0de` can be converted `12,11,0,12,13` (in base 32) or `01100,01011,00000,01100,01101` in binary (5-bit)

The binary value is divided by distinguishing 1 bit out of 2 in order to create 2 other binary numbers, the first being associated with the longitude, the second the latitude.

__Example:__ `0110001011000000110001101` becomes `0_1_0_1_1_0_0_0_1_0_0_1_1` (longitude) and `_1_0_0_0_1_0_0_0_1_0_1_0_` (latitude)

The values are then treated as a dichotomy indicator with the interval `-180;+180` for longitude and `-90;+90` for latitude. The idea is to split the interval in 2 at each step and take `0` for the right part and `1` for the left part. The more bits there are, the more accurate the value.

__Example:__ The longitude `0101100010011`

Bit | Left Interval | Right Interval |
---|---|---|

0 | -180;0 | |

1 | -90;0 | |

0 | -90;-45 | |

1 | -66.5;-45 | |

… | … | … |

__Example:__ The geohash `dc0de` string corresponds to `+6.08642578125 ; -55.39306640625`

From the GPS coordinates, the geohash is calculated by creating two binary strings, one for the longitude and one for the latitude, by dichotomy of the corresponding intervals. By splitting each interval into 2 equal parts and noting `0` the left interval and `1` the right interval.

__Example:__ Code a latitude of `+12.34` starting from the interval `-90;+90`, take the right interval (noted `1`), ie `0;+90`, then the left interval (noted `0`) is `0;+45`, then the left interval `=0` is `0;+22.5`, etc… until the desired accuracy is obtained. Same for the longitude `+12.34` with the interval `-180;+180`. The 2 numbers obtained are respectively `10010001100011001` and `100010001100011001`.

From the 2 binary numbers, recompose a single binary number alternately composed of a bit of longitude and a bit of latitude

__Example:__ `100010001100011001` and `10010001100011001` make `11000001100000011110000001111000011`

Convert the resulting binary number to base 32 using the characters `0123456789bcdefghjkmnpqrstuvwxyz`

__Example:__ `11000001100000011110000001111000011` in base 2 is `s60y0y3` in this special base 32

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Cite as source (bibliography):

*Geohash* on dCode.fr [online website], retrieved on 2024-11-05,

geohash,geo,hash,coordinate,latitude,longitude,gps

https://www.dcode.fr/geohash-coordinates

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