MarkLogic 12 EA 1 Product Documentation
geo:geohash-encodegeo:geohash-encode(
$region as cts:region,
[$geohash-precision as xs:integer?],
[$options as xs:string*]
) as xs:string
Summary
Compute a set of covering geohashes for the given region, to the given
level of precision.
| Parameters |
| region |
The region to encode.
|
| geohash-precision |
The desired precision (length of the geohash). The precision should be
between 1 and 12. If the precision is less than 1, or unspecified, the
default geohash-precision of 6 is used. A geohash-precision greater than 12
is treated as the same as 12. In the worst case (at the equator) a precision
of 12 gives resolution of less than a centimeter.
|
| options |
Options for the operation. The default is ().
Options include:
- "coordinate-system=string"
- Use the given coordinate system. Valid values are:
- wgs84
- The WGS84 coordinate system with degrees as the angular unit.
- wgs84/radians
- The WGS84 coordinate system with radians as the angular unit.
- wgs84/double
- The WGS84 coordinate system at double precision with degrees as the angular unit.
- wgs84/radians/double
- The WGS84 coordinate system at double precision with radians as the angular unit.
- etrs89
- The ETRS89 coordinate system.
- etrs89/double
- The ETRS89 coordinate system at double
precision.
Geohashing is not allowed for non-geodetic coordinate systems.
Attempting to use this function with the raw or raw/double coordinate
system will result in an XDMP-GEOHASH-COORD error.
- "precision=string"
- Use the coordinate system at the given precision. Allowed values:
float (default) and double.
- "units=value"
- Measure distance, radii of circles, and tolerance in the specified units.
Allowed values:
miles (default), km,
feet, meters.
- "tolerance=distance"
- Tolerance is the largest allowable variation in geometry calculations.
If the distance between two points is less than tolerance, then the two
points are considered equal. For the raw coordinate system, use the units
of the coordinates. For geographic coordinate systems, use the units
specified by the units option.
- geohashes=value
- Specify which geohashes to return. Allowed values:
- all
- Return a complete set of covering hashes for the region
(boundary + interior). This is the default behavior.
- boundary
- Return only geohashes that intersect with the boundary of the
region.
- interior
- Return only geohashes completely contained in the interior
of the region.
- exterior
- Return all geohashes disjoint from the region. That is, all
geohashes completely contained in the exterior of the region.
|
Usage Notes
The default geohash-precision is 6. Care should be taken in the selection of
higher geohash-precisions for non-point regions: Converging on a sufficiently
precise covering set on polygons with many vertices can be costly.
Geohashes of circles are calculated by approximating the circle by a polygon.
This approximation is accurate to within 0.001% of the radius of the circle. If
additional precision is required, use
geo:circle-polygon
to convert the circle before calling this function.
The value of the precision option takes precedence over
that implied by the governing coordinate system name, including the
value of the coordinate-system option. For example, if the
governing coordinate system is "wgs84/double" and the precision
option is "float", then the operation uses single precision.
See Also
Example
geo:geohash-encode(cts:point(1.23354,66.67),12)
=> t2prj0e9gssb
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