Use the ST_WellKnownBinary transform group
to transmit data using the well-known binary (WKB) representation.
When binding out a value from the database to a client application, the same
function provided by ST_AsBinary() is used to convert a geometry to the WKB representation. When the
well-known binary representation of a geometry is transferred to the database, the ST_Geometry(BLOB)
function is used implicitly to perform the conversions to an ST_Geometry value. Using the transform
group for binding in values causes the geometries to be represented in the spatial reference system
with the numeric identifier 0 (zero).
Example
In the following examples, the lines
of results have been reformatted for readability. The spacing in your
results might vary according to your online display.
- Example 1
The following SQL script shows how to use the ST_WellKnownBinary
transform group to retrieve a geometry in its well-known binary representation
without using the explicit ST_AsBinary function.
CREATE TABLE transforms_sample (
id INTEGER,
geom db2gse.ST_Geometry)
INSERT
INTO transforms_sample
VALUES ( 1, db2gse.ST_Polygon('polygon ((10 10, 20 10, 20 20,
10 20, 10 10))', 0))
SET CURRENT DEFAULT TRANSFORM GROUP = ST_WellKnownBinary
SELECT id, geom
FROM transforms_sample
WHERE id = 1
Results:
ID GEOM
---- ----------------------------------------------
1 x'01030000000100000005000000000000000000244000
0000000000244000000000000024400000000000003440
0000000000003440000000000000344000000000000034
4000000000000024400000000000002440000000000000
2440'
- Example 2
The following C code shows how to use the ST_WellKnownBinary
transform group for inserting geometries using the explicit ST_Geometry
function for the host-variable
wkb_buffer, which
is of type BLOB and contains the well-known binary representation
of a geometry that is to be inserted.
EXEC SQL BEGIN DECLARE SECTION;
sqlint32 id = 0;
SQL TYPE IS db2gse.ST_Geometry AS BLOB(1000) wkb_buffer;
EXEC SQL END DECLARE SECTION;
// set the transform group for all subsequent SQL statements
EXEC SQL
SET CURRENT DEFAULT TRANSFORM GROUP = ST_WellKnownBinary;
// initialize host variables
...
// insert geometry using WKB into column of type ST_Geometry
EXEC SQL
INSERT
INTO transforms_sample(id, geom)
VALUES ( :id, :wkb_buffer );