ST_GML transform group

Use the ST_GML transform group to transmit data by using the geography markup language (GML).

When binding out a value from the database to a client application, the same function provided by ST_AsGML() is used to convert a geometry to its GML representation. When the GML representation of a geometry is transferred to the database, the ST_Geometry(CLOB) 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).

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 the ST_GML transform group can be used to retrieve a geometry in its GML representation without using the explicit ST_AsGML function.


CREATE TABLE transforms_sample (
   id	 INTEGER,
   geom	 db2gse.ST_Geometry)

INSERT
  INTO	 transforms_sample
  VALUES ( 1, db2gse.ST_Geometry('multipoint z (10 10 
           3, 20 20 4, 15 20 30)', 0) )
  SET CURRENT DEFAULT TRANSFORM GROUP = ST_GML

SELECT id, geom
FROM	 transforms_sample
WHERE	 id = 1

Results:


ID		  GEOM
-----  -------------------------------------------------------------
    1 <gml:MultiPoint srsName=UNSPECIFIED><gml:PointMember>
      <gml:Point><gml:coord><gml:X>10</gml:X>
      <gml:Y>10</gml:Y><gml:Z>3</gml:Z>
      </gml:coord></gml:Point></gml:PointMember>
      <gml:PointMember><gml:Point><gml:coord>
      <gml:X>20</gml:X><gml:Y>20</gml:Y>
      <gml:Z>4</gml:Z></gml:coord></gml:Point>
      </gml:PointMember><gml:PointMember><gml:Point>
      <gml:coord><gml:X>15</gml:X><gml:Y>20
      </gml:Y><gml:Z>30</gml:Z></gml:coord>
      </gml:Point></gml:PointMember></gml:MultiPoint>

Example 2

The following C code shows how to use the ST_GML transform group for inserting geometries without using the explicit ST_Geometry function for the host-variable gml_buffer, which is of type CLOB and contains the GML representation of the point (20 ,20) that is to be inserted.


EXEC SQL BEGIN DECLARE SECTION;
   sqlint32 id = 0;
   SQL TYPE IS db2gse.ST_Geometry AS CLOB(1000) gml_buffer;
EXEC SQL END DECLARE SECTION;

// set the transform group for all subsequent SQL statements
EXEC SQL
   SET CURRENT DEFAULT TRANSFORM GROUP = ST_GML;
	id = 100;
strcpy(gml_buffer.data, "<gml:point><gml:coord>"
			"<gml:X>20</gml:X> <gml:Y>20</gml:Y></gml:coord></gml:point>");

//initialize host variables
wkt_buffer.length = strlen(gml_buffer.data);

// insert point using WKT into column of type ST_Geometry
EXEC SQL
   INSERT
	  INTO transforms_sample(id, geom)
	  VALUES ( :id, :gml_buffer );