14.16.7.2 Point Property Functions

A Point consists of X and Y coordinates, which may be obtained using the ST_X() and ST_Y() functions, respectively. These functions also permit an optional second argument that specifies an X or Y coordinate value, in which case the function result is the Point object from the first argument with the appropriate coordinate modified to be equal to the second argument.

For Point objects that have a geographic spatial reference system (SRS), the longitude and latitude may be obtained using the ST_Longitude() and ST_Latitude() functions, respectively. These functions also permit an optional second argument that specifies a longitude or latitude value, in which case the function result is the Point object from the first argument with the longitude or latitude modified to be equal to the second argument.

Unless otherwise specified, functions in this section handle their geometry arguments as follows:

• If any argument is NULL, the return value is NULL.

• If any geometry argument is a valid geometry but not a Point object, an ER_UNEXPECTED_GEOMETRY_TYPE error occurs.

• If any geometry argument is not a syntactically well-formed geometry, an ER_GIS_INVALID_DATA error occurs.

• If any geometry argument is a syntactically well-formed geometry in an undefined spatial reference system (SRS), an ER_SRS_NOT_FOUND error occurs.

• If an X or Y coordinate argument is provided and the value is -inf, +inf, or NaN, an ER_DATA_OUT_OF_RANGE error occurs.

• If a longitude or latitude value is out of range, an error occurs:

  • If a longitude value is not in the range (−180, 180], an ER_LONGITUDE_OUT_OF_RANGE error occurs.

  • If a latitude value is not in the range [−90, 90], an ER_LATITUDE_OUT_OF_RANGE error occurs.

  Ranges shown are in degrees. The exact range limits deviate slightly due to floating-point arithmetic.

• Otherwise, the return value is non-NULL.

These functions are available for obtaining point properties:

• ST_Latitude(p [, new_latitude_val])

  With a single argument representing a valid Point object p that has a geographic spatial reference system (SRS), ST_Latitude() returns the latitude value of p as a double-precision number.

  With the optional second argument representing a valid latitude value, ST_Latitude() returns a Point object like the first argument with its latitude equal to the second argument.

  ST_Latitude() handles its arguments as described in the introduction to this section, with the addition that if the Point object is valid but does not have a geographic SRS, an ER_SRS_NOT_GEOGRAPHIC error occurs.

  mysql> SET @pt = ST_GeomFromText('POINT(45 90)', 4326);
  mysql> SELECT ST_Latitude(@pt);
  +------------------+
  | ST_Latitude(@pt) |
  +------------------+
  |               45 |
  +------------------+
  mysql> SELECT ST_AsText(ST_Latitude(@pt, 10));
  +---------------------------------+
  | ST_AsText(ST_Latitude(@pt, 10)) |
  +---------------------------------+
  | POINT(10 90)                    |
  +---------------------------------+

• ST_Longitude(p [, new_longitude_val])

  With a single argument representing a valid Point object p that has a geographic spatial reference system (SRS), ST_Longitude() returns the longitude value of p as a double-precision number.

  With the optional second argument representing a valid longitude value, ST_Longitude() returns a Point object like the first argument with its longitude equal to the second argument.

  ST_Longitude() handles its arguments as described in the introduction to this section, with the addition that if the Point object is valid but does not have a geographic SRS, an ER_SRS_NOT_GEOGRAPHIC error occurs.

  mysql> SET @pt = ST_GeomFromText('POINT(45 90)', 4326);
  mysql> SELECT ST_Longitude(@pt);
  +-------------------+
  | ST_Longitude(@pt) |
  +-------------------+
  |                90 |
  +-------------------+
  mysql> SELECT ST_AsText(ST_Longitude(@pt, 10));
  +----------------------------------+
  | ST_AsText(ST_Longitude(@pt, 10)) |
  +----------------------------------+
  | POINT(45 10)                     |
  +----------------------------------+

• ST_X(p [, new_x_val])

  With a single argument representing a valid Point object p, ST_X() returns the X-coordinate value of p as a double-precision number. The X coordinate is considered to refer to the axis that appears first in the Point spatial reference system (SRS) definition.

  With the optional second argument, ST_X() returns a Point object like the first argument with its X coordinate equal to the second argument. If the Point object has a geographic SRS, the second argument must be in the proper range for longitude or latitude values.

  ST_X() handles its arguments as described in the introduction to this section.

  mysql> SELECT ST_X(Point(56.7, 53.34));
  +--------------------------+
  | ST_X(Point(56.7, 53.34)) |
  +--------------------------+
  |                     56.7 |
  +--------------------------+
  mysql> SELECT ST_AsText(ST_X(Point(56.7, 53.34), 10.5));
  +-------------------------------------------+
  | ST_AsText(ST_X(Point(56.7, 53.34), 10.5)) |
  +-------------------------------------------+
  | POINT(10.5 53.34)                         |
  +-------------------------------------------+

• ST_Y(p [, new_y_val])

  With a single argument representing a valid Point object p, ST_Y() returns the Y-coordinate value of p as a double-precision number.The Y coordinate is considered to refer to the axis that appears second in the Point spatial reference system (SRS) definition.

  With the optional second argument, ST_Y() returns a Point object like the first argument with its Y coordinate equal to the second argument. If the Point object has a geographic SRS, the second argument must be in the proper range for longitude or latitude values.

  ST_Y() handles its arguments as described in the introduction to this section.

  mysql> SELECT ST_Y(Point(56.7, 53.34));
  +--------------------------+
  | ST_Y(Point(56.7, 53.34)) |
  +--------------------------+
  |                    53.34 |
  +--------------------------+
  mysql> SELECT ST_AsText(ST_Y(Point(56.7, 53.34), 10.5));
  +-------------------------------------------+
  | ST_AsText(ST_Y(Point(56.7, 53.34), 10.5)) |
  +-------------------------------------------+
  | POINT(56.7 10.5)                          |
  +-------------------------------------------+