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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, seehttp://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 nativeJSON data type and a set of SQL functions to enable operations on JSON values. For more information, seeSection 11.5, “The JSON Data Type”, andSection 12.17, “JSON Functions”.

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

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

    If any argument isNULL, the return value isNULL. 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 ValueMeaning
    0No options. This is the default ifoptions is not specified.
    1Add a bounding box to the output.
    2Add a short-format CRS URN to the output. The default format is a short format (EPSG:srid).
    4Add 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 stringstr representing a GeoJSON object and returns a geometry.

    If any argument isNULL, the return value isNULL. 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 permittedoptions values.

    Option ValueMeaning
    1Reject the document and produce an error. This is the default ifoptions is not specified.
    2, 3, 4Accept 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.

    Thesrid 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 acrs property. The parsing function parses named CRS URNs in theurn:ogc:def:crs:EPSG::srid andEPSG: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 optionalsrid argument is given, any CRS is ignored even if it is invalid.

    As specified in the GeoJSON specification, parsing is case-sensitive for thetype 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)                         |+--------------------------------------+