Use the ST_WellKnownText transform group
to transmit data using the well-known text (WKT) representation.
When binding out a value from the database to a client application, the same
function provided by ST_AsText() is used to convert a geometry to the WKT representation. When the
well-known text representation of a geometry is transferred to the database, the ST_Geometry(CLOB)
function is implicitly used 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).
Examples
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_WellKnownText
transform group to retrieve a geometry in its well-known text representation
without using the explicit ST_AsText function.
CREATE TABLE transforms_sample (
id INTEGER,
geom db2gse.ST_Geometry)
INSERT
INTO transforms_sample
VALUES (1, db2gse.ST_LineString('linestring
(100 100, 200 100)', 0))
SET CURRENT DEFAULT TRANSFORM GROUP = ST_WellKnownText
SELECT id, geom
FROM transforms_sample
WHERE id = 1
Results:
ID GEOM
--- -------------------------------------------------------------------
1 LINESTRING ( 100.00000000 100.00000000, 200.00000000 100.00000000)
- Example 2
The following C code shows how to use the ST_WellKnownText
transform group to insert geometries using the explicit ST_Geometry
function for the host-variable
wkt_buffer, which
is of type CLOB and contains the well-known text representation of
the point (10 10) that is to be inserted.
EXEC SQL BEGIN DECLARE SECTION;
sqlint32 id = 0;
SQL TYPE IS db2gse.ST_Geometry AS CLOB(1000) wkt_buffer;
EXEC SQL END DECLARE SECTION;
// set the transform group for all subsequent SQL statements
EXEC SQL
SET CURRENT DEFAULT TRANSFORM GROUP = ST_WellKnownText;
id = 100;
strcpy(wkt_buffer.data, "point ( 10 10 )");
wkt_buffer.length = strlen(wkt_buffer.data);
// insert point using WKT into column of type ST_Geometry
EXEC SQL
INSERT
INTO transforms_sample(id, geom)
VALUES (:id, :wkt_buffer);