ST_PolyFromWKB function

The ST_PolyFromWKB function takes a well-known binary representation of a polygon and, optionally, a spatial reference system identifier as input parameters and returns the corresponding polygon.

If the given well-known binary representation is null, then null is returned.

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 well-known binary representation.

Syntax

Parameters

wkb

A value of type BLOB(2G) that contains the well-known binary representation of the resulting polygon.

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 0 (zero) 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

db2gse.ST_Polygon

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.

This example illustrates how ST_PolyFromWKB can be used to create a polygon from its well-known binary representation. The geometry is a polygon in spatial reference system 1. In this example, the polygon gets stored with ID = 1115 in the GEOMETRY column of the SAMPLE_POLYS table, and then the WKB column is updated with its well-known binary representation (using the ST_AsBinary function). Finally, the ST_PolyFromWKB function is used to return the multipolygon from the WKB column. The X and Y coordinates for this geometry are: (50, 20) (50, 40) (70, 30).

The SAMPLE_POLYS table has a GEOMETRY column, where the polygon is stored, and a WKB column, where the polygon's well-known binary representation is stored.


SET CURRENT FUNCTION PATH = CURRENT FUNCTION PATH, db2gse
CREATE TABLE sample_polys (id INTEGER, geometry ST_Polygon,
  wkb BLOB(32K))

INSERT INTO sample_polys
  VALUES (10, ST_Polygon ('polygon ((50 20, 50 40, 70 30, 50 20))', 1) )

UPDATE sample_polys AS temporary_correlated
  SET wkb = ST_AsBinary( geometry )
  WHERE id = temporary_correlated.id

In the following SELECT statement, the ST_PolyFromWKB function is used to retrieve the polygon from the WKB column.


SELECT id, CAST( ST_AsText( ST_PolyFromWKB (wkb) ) 
  AS VARCHAR(120) ) POLYGON
  FROM sample_polys
  WHERE id = 1115

Results:


ID         POLYGON
---------- --------------------------------------------------------------
      1115 POLYGON (( 50.00000000 20.00000000, 70.00000000 
              30.00000000,50.00000000 40.00000000, 50.00000000 
              20.00000000))