ST_AsText function
The ST_AsText function takes a geometry object as an input parameter and returns its Well-known text (WKT) format.
If the specified geometry is null, then null is returned.
Syntax
Parameter
- geometry
- A value of type ST_Geometry or one of its subtypes to be converted to the corresponding WKT format.
Return type
CLOB(2G)
Example
In the following example, the lines of results have been reformatted for readability. The spacing in your results will vary according to your online display.
After capturing
and inserting the data into the SAMPLE_GEOMETRIES table, an analyst
wants to verify that the values inserted are correct by looking at
the WKT format of the geometries.
CREATE TABLE sample_geometries(id SMALLINT, spatial_type varchar(18),
geometry ST_GEOMETRY)
INSERT INTO sample_geometries(id, spatial_type, geometry)
VALUES
(1, 'st_point', ST_Point(50, 50, 0)),
(2, 'st_linestring', ST_LineString('linestring
(200 100, 210 130, 220 140)', 0)),
(3, 'st_polygon', ST_Polygon('polygon((110 120, 110 140,
130 140, 130 120, 110 120))', 0))
The following SELECT statement lists the spatial
type and the WKT format of the geometries. The geometry
is converted to text by the ST_AsText function. It is then cast
to a varchar(120) because the default output of the ST_AsText function
is CLOB(2G).
SELECT id, spatial_type, cast(ST_AsText(geometry) AS varchar(150)) AS wkt
FROM sample_geometries
Results:
ID SPATIAL_TYPE WKT
------ ------------------ -------------------------------------------------------
1 st_point POINT (50 50)
2 st_linestring LINESTRING (200 100, 210 130, 220 140)
3 st_polygon POLYGON ((110 120, 130 120, 130 140, 110 140, 110 120))