geographiclib (version 0.4.0)

geohash_fwd: Convert coordinates to/from Geohash

Description

Convert geographic coordinates (longitude/latitude) to Geohash strings, or convert Geohash strings back to coordinates.

Usage

geohash_fwd(x, len = 12L)
geohash_rev(geohash)
geohash_resolution(len)
geohash_length(resolution = NULL, lat_resolution = NULL, lon_resolution = NULL)

Value

• geohash_fwd(): Character vector of Geohash strings.

• geohash_rev(): Data frame with columns:

  • lon: Longitude in decimal degrees (center of cell)

  • lat: Latitude in decimal degrees (center of cell)

  • len: Length of the Geohash string

  • lat_resolution: Latitude resolution in degrees (half-height of cell)

  • lon_resolution: Longitude resolution in degrees (half-width of cell)

• geohash_resolution(): Data frame with columns:

  • len: Geohash length

  • lat_resolution: Latitude resolution in degrees

  • lon_resolution: Longitude resolution in degrees

• geohash_length(): Integer, minimum Geohash length to achieve the specified resolution.

Arguments

x

A two-column matrix or data frame of coordinates (longitude, latitude) in decimal degrees, or a list with longitude and latitude components. Can also be a length-2 numeric vector for a single point.

len

Integer specifying the length of the Geohash string (1-18). Default is 12, which gives approximately 19mm precision. Can be a vector to specify different lengths for each point.

geohash

Character vector of Geohash strings to convert back to coordinates.

resolution

Numeric. Desired resolution in degrees for geohash_length().

lat_resolution

Numeric. Desired latitude resolution in degrees.

lon_resolution

Numeric. Desired longitude resolution in degrees.

Details

Geohash is a geocoding system that encodes geographic coordinates into a short string of letters and digits. It has a useful property: truncating a Geohash reduces precision but the truncated code still refers to a location containing the original point.

The Geohash length determines precision:

• Length 1: ~5000 km

• Length 4: ~20 km

• Length 6: ~610 m

• Length 8: ~19 m

• Length 10: ~0.6 m

• Length 12: ~19 mm (default)

• Length 18: ~0.0001 mm (maximum)

Both geohash_fwd() and geohash_rev() are fully vectorized.

See Also

mgrs_fwd() for Military Grid Reference System encoding, which provides a different grid-based coordinate system.

Examples

# Single point conversion
(gh <- geohash_fwd(c(147.325, -42.881)))
geohash_rev(gh)

# Multiple points with varying precision
pts <- cbind(
  lon = c(147, -74, 0),
  lat = c(-42, 40.7, 51.5)
)
geohash_fwd(pts, len = c(6, 8, 12))

# Truncation preserves containment
gh <- geohash_fwd(c(147.325, -42.881), len = 12)
substr(gh, 1, 6)  # Lower precision, but still contains original point

# Resolution for different lengths
geohash_resolution(1:12)

# Find length needed for ~1km precision
geohash_length(1/111)  # ~1 degree / 111 km