12.16.11 Spatial GeoJSON Functions

This section describes functions for converting between GeoJSON documents and spatial values. GeoJSON is an open standard for encoding geometric/geographical features. For more information, see http://geojson.org. The functions discussed here follow GeoJSON specification revision 1.0.

GeoJSON supports the same geometric/geographic data types that MySQL supports. Feature and FeatureCollection objects are not supported, except that geometry objects are extracted from them. CRS support is limited to values that identify an SRID.

MySQL also supports a native JSON data type and a set of SQL functions to enable operations on JSON values. For more information, see Section 11.5, “The JSON Data Type”, and Section 12.17, “JSON Functions”.

• ST_AsGeoJSON(g [, max_dec_digits [, options]])

  Generates a GeoJSON object from the geometry g. The object string has the connection character set and collation.

  If any argument is NULL, the return value is NULL. If any non-NULL argument is invalid, an error occurs.

  max_dec_digits, if specified, limits the number of decimal digits for coordinates and causes rounding of output. If not specified, this argument defaults to its maximum value of 2³² − 1. The minimum is 0.

  options, if specified, is a bitmask. The following table shows the permitted flag values. If the geometry argument has an SRID of 0, no CRS object is produced even for those flag values that request one.

  Flag Value	Meaning
  0	No options. This is the default if options is not specified.
  1	Add a bounding box to the output.
  2	Add a short-format CRS URN to the output. The default format is a short format (EPSG:srid).
  4	Add a long-format CRS URN (urn:ogc:def:crs:EPSG::srid). This flag overrides flag 2. For example, option values of 5 and 7 mean the same (add a bounding box and a long-format CRS URN).

  mysql> SELECT ST_AsGeoJSON(ST_GeomFromText('POINT(11.11111 12.22222)'),2);
  +-------------------------------------------------------------+
  | ST_AsGeoJSON(ST_GeomFromText('POINT(11.11111 12.22222)'),2) |
  +-------------------------------------------------------------+
  | {"type": "Point", "coordinates": [11.11, 12.22]}            |
  +-------------------------------------------------------------+

• ST_GeomFromGeoJSON(str [, options [, srid]])

  Parses a string str representing a GeoJSON object and returns a geometry.

  If any argument is NULL, the return value is NULL. If any non-NULL argument is invalid, an error occurs.

  options, if given, describes how to handle GeoJSON documents that contain geometries with coordinate dimensions higher than 2. The following table shows the permitted options values.

  Option Value	Meaning
  1	Reject the document and produce an error. This is the default if options is not specified.
  2, 3, 4	Accept the document and strip off the coordinates for higher coordinate dimensions.

  options values of 2, 3, and 4 currently produce the same effect. If geometries with coordinate dimensions higher than 2 are supported in the future, these values can be expected to produce different effects.

  The srid argument, if given, must be a 32-bit unsigned integer. If not given, the geometry return value has an SRID of 4326.

  GeoJSON geometry, feature, and feature collection objects may have a crs property. The parsing function parses named CRS URNs in the urn:ogc:def:crs:EPSG::srid and EPSG:srid namespaces, but not CRSs given as link objects. Also, urn:ogc:def:crs:OGC:1.3:CRS84 is recognized as SRID 4326. If an object has a CRS that is not understood, an error occurs, with the exception that if the optional srid argument is given, any CRS is ignored even if it is invalid.

  As specified in the GeoJSON specification, parsing is case-sensitive for the type member of the GeoJSON input (Point, LineString, and so forth). The specification is silent regarding case sensitivity for other parsing, which in MySQL is not case-sensitive.

  This example shows the parsing result for a simple GeoJSON object:

  mysql> SET @json = '{ "type": "Point", "coordinates": [102.0, 0.0]}';
  mysql> SELECT ST_AsText(ST_GeomFromGeoJSON(@json));
  +--------------------------------------+
  | ST_AsText(ST_GeomFromGeoJSON(@json)) |
  +--------------------------------------+
  | POINT(102 0)                         |
  +--------------------------------------+