ST_PolyFromText function

The ST_PolyFromText function takes a well-known text (WKT) format or a GeoJSON format of a polygon and, optionally, a spatial reference system identifier as input parameters and returns the corresponding polygon.

ST_PolyFromText constructs a geometry from one of the following inputs:

A WKT format
GeoJSON format

The recommended function for achieving the same result is the ST_Polygon function. It is recommended because of its flexibility: ST_Polygon takes additional forms of input as well as the WKT or GeoJSON formats.

If the specified WKT or GeoJSON format is null, then null is returned.

For details about the supported formats, see Supported data formats.

Syntax

Parameters

wkt

A value of type VARCHAR or CLOB(2G) that contains the WKT format of the resulting polygon.

geojson

A value of type VARCHAR or CLOB(2G) that represents the resulting polygon using GeoJSON.

srs_id

A value of type INTEGER that identifies the spatial reference system for the resulting polygon.

If the srs_id parameter is omitted, the spatial reference system with the numeric identifier 4326 is used.

If srs_id does not identify a spatial reference system listed in the catalog view DB2GSE.ST_SPATIAL_REFERENCE_SYSTEMS, then an exception condition is raised (SQLSTATE 38SU1).

Return type

ST_Polygon

Examples

Example 1:

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.

This example illustrates how ST_PolyFromText can be used to create and insert a polygon from its WKT format. The record that is inserted has ID = 1110, and the geometry is a polygon in spatial reference system 1. The polygon is in the WKT format of a polygon. The X and Y coordinates for this geometry are: (50, 20) (50, 40) (70, 30).


CREATE TABLE sample_polys (id INTEGER, geometry ST_Polygon)

INSERT INTO sample_polys
  VALUES (1110, ST_PolyFromText ('polygon ((50 20, 50 40, 70 30, 50 20))', 1) )

The following SELECT statement returns the polygon that was recorded in the table:


SELECT id, CAST( ST_AsText( geometry ) AS VARCHAR(120) ) POLYGON
  FROM sample_polys
  WHERE id = 1110

Results:


ID         POLYGON
---------- --------------------------------------------------------------------
      1110 POLYGON ((50.000000 20.000000, 70.000000 30.000000, 
                     50.000000 40.000000, 50.000000 20.000000))

Example 2:

This example illustrates how ST_PolyFromText can be used to create and insert a polygon from its GeoJSON format using the geometry data from Example 1.

The record that is inserted has ID = 1111, and the geometry is a polygon in spatial reference system 4326 (the default). The polygon is in the GeoJSON format of a polygon.


CREATE TABLE sample_polys (id INTEGER, geometry ST_Polygon)

INSERT INTO sample_polys
  VALUES (1111, ST_PolyFromText ('{ "type": "polygon", "coordinates": [ [[50, 20], [50, 40], [70, 30], [50, 20]] ] }') )

The following SELECT statement returns the polygon that was recorded in the table:


SELECT id, CAST( ST_AsText( geometry ) AS VARCHAR(120) ) POLYGON
  FROM sample_polys
  WHERE id = 1111

Results:


ID         POLYGON
---------- --------------------------------------------------------------------
1111       POLYGON ((50.000000000 20.000000000, 70.000000000 30.000000000, 
                     50.000000000 40.000000000, 50.000000000 20.000000000))