Modify the number of dimention of a geometry

Question

Is it possible to modify, with a function, the number of dimension of a geometry?
I'm able to change the gtype but not the sdo_elem_info and sdo_ordinates.
....thanks for your help

Answer 1

Here is a function doing what you ask for.
It is not very efficient or elegant, but I think it works for most geometries :
Parameter Numd is the dimension you want of the returned geometry.
good luck
Hans
FUNCTION Convert_to( Numd PLS_INTEGER, Geo IN Mdsys.Sdo_geometry )
RETURN Mdsys.Sdo_geometry
-- converts from 4D to 2D or 3D ...
-- or converts from 3D to 2D ...
IS
Resultat Mdsys.Sdo_geometry;
V_numdims PLS_INTEGER;
V_numords PLS_INTEGER;
V_numelem PLS_INTEGER;
V_typeelem PLS_INTEGER;
V_startpos PLS_INTEGER;
V_startposnext PLS_INTEGER;
V_endpos PLS_INTEGER;
I PLS_INTEGER;
P PLS_INTEGER;
V_curpos PLS_INTEGER;
V_is_multipolygon BOOLEAN;
V_gtype PLS_INTEGER;
V_count PLS_INTEGER;
V_count_unknown PLS_INTEGER;
V_ok PLS_INTEGER;
BEGIN
Resultat := NULL;
IF ( Numd < 2 )
OR ( Numd > 3 ) THEN
RETURN Resultat;
END IF;
IF Geo IS NULL THEN -- no geometry to work with .
RETURN Resultat;
END IF;
V_gtype := Geo.Sdo_gtype;
IF MOD( V_gtype, 1000 ) = 0 THEN -- Spatial ignores this geometry .
Resultat := Geo;
RETURN Resultat;
END IF;
IF V_gtype > 1999
AND V_gtype < 3000 THEN-- This is a 2D geometry - just exit FROM here ..
Resultat := Geo;
RETURN Resultat;
END IF;
IF V_gtype > 2999
AND V_gtype < 4000
AND Numd = 3 THEN
-- This is a 3D geometry - AND that's want we want - just exit FROM here ..
Resultat := Geo;
RETURN Resultat;
END IF;
IF NOT Geo.Sdo_point IS NULL THEN -- single point ...
Resultat := Geo;
Resultat.Sdo_gtype := 2000 + MOD( V_gtype, 1000 );
Resultat.Sdo_point.Z := NULL;
RETURN Resultat;
END IF;
IF Geo.Sdo_elem_info IS NULL THEN
RETURN Resultat;
END IF;
IF Geo.Sdo_ordinates IS NULL THEN
RETURN Resultat;
END IF;
V_numdims := TRUNC( Geo.Sdo_gtype / 1000 );
-- NUMBER of dimensions 2D, 3D OR 4D .
V_numelem := Geo.Sdo_elem_info.COUNT / 3;
-- NUMBER of elements in this geometry .
IF ( MOD( V_gtype, 1000 ) = 1 )
-- Point type - check for single point in sdo_ordinates .....
THEN
V_ok := 1;
V_count := Geo.Sdo_ordinates.COUNT;
V_count_unknown := 0;
IF ( V_numelem = 2 ) THEN
IF ( Geo.Sdo_elem_info( 2 ) = 0 )
-- first element is : Unsupported element type. Ignored by the Spatial functions AND PROCEDUREs.
THEN
V_count_unknown := Geo.Sdo_elem_info( 4 ) - 1;
-- num of ordinates in the unknown part ...
ELSE
V_ok := 0;
END IF;
END IF;
IF (
V_ok = 1
AND V_numelem < 3
AND V_count - V_count_unknown > 1
AND (
( V_count - V_count_unknown < 5
AND V_gtype > 3999 )
-- 4d with one point in sdo_ordinates ..
OR ( V_count - V_count_unknown < 4
AND V_gtype > 2999 )))
-- 3d with one point in sdo_ordinates ..
THEN
IF Numd = 2 THEN
Resultat :=
Mdsys.Sdo_geometry( 2001, -- GType 2D .
Geo.Sdo_srid,
Mdsys.Sdo_point_type( Geo.Sdo_ordinates( V_count_unknown + 1 ),
-- X ..
Geo.Sdo_ordinates( V_count_unknown + 2 ), -- Y ..
NULL ), -- sdo_point_type(x,y,NULL) .
NULL,
NULL );
ELSE
Resultat :=
Mdsys.Sdo_geometry( 3001, -- GType 3D .
Geo.Sdo_srid,
Mdsys.Sdo_point_type( Geo.Sdo_ordinates( V_count_unknown + 1 ),
-- X ..
Geo.Sdo_ordinates( V_count_unknown + 2 ), -- Y ..
Geo.Sdo_ordinates( V_count_unknown + 3 )), -- Z ..
-- sdo_point_type(x,y,NULL) .
NULL,
NULL );
END IF;
RETURN Resultat;
END IF;
END IF; -- END of Point type ....
Resultat :=
Mdsys.Sdo_geometry( Numd * 1000 + MOD( V_gtype, 1000 ),
-- GType 2D eller 3D .
Geo.Sdo_srid,
NULL, -- sdo_point_type .
Mdsys.Sdo_elem_info_array( ),
Mdsys.Sdo_ordinate_array( ));
IF V_numelem = 0 THEN
RETURN Resultat;
END IF;
IF MOD( Geo.Sdo_gtype, 1000 ) < 7 THEN
V_is_multipolygon := FALSE;
ELSE
V_is_multipolygon := TRUE;
END IF;
I := 1;
V_curpos := 1;
LOOP -- for all the elements ...
V_startpos := Geo.Sdo_elem_info( ( I - 1 ) * 3 + 1 );
-- StartPosition for the ordinates of this element
V_typeelem := Geo.Sdo_elem_info( ( I - 1 ) * 3 + 2 );
-- the pos after StartPosition, ie. eType ...
IF I = V_numelem THEN -- is this the last element ?
V_startposnext := Geo.Sdo_ordinates.COUNT( ) + 1;
ELSE
V_startposnext := Geo.Sdo_elem_info( ( I * 3 ) + 1 );
END IF;
Resultat.Sdo_elem_info.EXTEND( 3 );
Resultat.Sdo_elem_info( ( I - 1 ) * 3 + 1 ) := V_curpos;
-- StartPosition for the ordinates of this element
Resultat.Sdo_elem_info( ( I - 1 ) * 3 + 2 ) :=
Geo.Sdo_elem_info( ( I - 1 ) * 3 + 2 );
-- eType ...;
Resultat.Sdo_elem_info( ( I - 1 ) * 3 + 3 ) :=
Geo.Sdo_elem_info( ( I - 1 ) * 3 + 3 );
-- Interpretation ...;
IF V_typeelem > 0 THEN -- ignore element
IF (NOT V_is_multipolygon )
OR ( V_is_multipolygon
AND I > 1 ) THEN
IF ( V_startposnext > V_startpos + 1 ) THEN
P := V_startpos;
-- p is now the position of the first ordinate for this element
LOOP -- For all ordinates ...
IF Numd = 3 THEN
Resultat.Sdo_ordinates.EXTEND( 3 );
ELSE
Resultat.Sdo_ordinates.EXTEND( 2 );
END IF;
Resultat.Sdo_ordinates( V_curpos ) := Geo.Sdo_ordinates( P );
-- X ...
Resultat.Sdo_ordinates( V_curpos + 1 ) :=
Geo.Sdo_ordinates( P + 1 );
-- Y ...
IF Numd = 3 THEN
Resultat.Sdo_ordinates( V_curpos + 2 ) :=
Geo.Sdo_ordinates( P + 1 );
-- Z ...
END IF;
P := P + V_numdims; -- jump to the next x ordinate
V_curpos := V_curpos + Numd; -- var +2 tidligere
EXIT WHEN P = V_startposnext;
END LOOP;
END IF;
-- ELSE : MULTIPOLYGON does not have its own ordinates
END IF;
ELSE
-- Element has unknown geometry , must copy all ordinates
Resultat.Sdo_ordinates.EXTEND( V_startposnext - V_startpos );
P := V_startpos;
-- p is now the position of the first ordinate for this element
LOOP -- For all ordinates ...
Resultat.Sdo_ordinates( V_curpos ) := Geo.Sdo_ordinates( P );
P := P + 1; -- next ordinate
V_curpos := V_curpos + 1;
EXIT WHEN P = V_startposnext;
END LOOP;
END IF;
I := I + 1;
EXIT WHEN I > V_numelem;
END LOOP;
RETURN Resultat;
EXCEPTION
WHEN OTHERS THEN
Resultat := NULL;
RETURN Resultat;
END Convert_t0;