ST_MLineFromWKB function

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

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

The recommended function for achieving the same result is the ST_MultiLineString function. It is recommended because of its flexibility: ST_MultiLineString 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 multilinestring.

srs_id

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

If the srs_id parameter is omitted, the spatial reference system with the numeric identifier 0 (zero) is used.

If the specified 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_MultiLineString

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_MLineFromWKB can be used to create a multilinestring from its well-known binary representation. The geometry is a multilinestring in spatial reference system 1. In this example, the multilinestring gets stored with ID = 10 in the GEOMETRY column of the SAMPLE_MLINES table, and then the WKB column is updated with its well-known binary representation (using the ST_AsBinary function). Finally, the ST_MLineFromWKB function is used to return the multilinestring from the WKB column. The X and Y coordinates for this geometry are:

Line 1: (61, 2) (64, 3) (65, 6)
Line 2: (58, 4) (59, 5) (61, 8)
Line 3: (69, 3) (67, 4) (66, 7) (68, 9)

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


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

INSERT INTO sample_mlines
  VALUES (10, ST_MultiLineString ('multilinestring 
       ( (61 2, 64 3, 65 6),
         (58 4, 59 5, 61 8),
         (69 3, 67 4, 66 7, 68 9) )', 1) )

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

In the following SELECT statement, the ST_MLineFromWKB function is used to retrieve the multilinestring from the WKB column.


SELECT id, CAST( ST_AsText( ST_MLineFromWKB (wkb) ) 
       AS VARCHAR(280) ) MULTI_LINE_STRING
  FROM sample_mlines
  WHERE id = 10

Results:


ID         MULTI_LINE_STRING
---------- --------------------------------------------------------------------
        10 MULTILINESTRING (( 61.00000000 2.00000000, 64.00000000 3.00000000, 
              65.00000000 6.00000000),
                            ( 58.00000000 4.00000000, 59.00000000 5.00000000,
              61.00000000 8.0000000),
                            ( 69.00000000 3.00000000, 67.00000000 4.00000000,
              66.00000000 7.00000000, 68.00000000 9.00000000 ))