Download IBM Informix Spatial DataBlade Module User's Guide

ST_Boundary()
ST_Boundary() takes a geometry object and returns its combined boundary as a
geometry object.
Syntax
ST_Boundary(g1 ST_Geometry)
Return Type
ST_Geometry
Example
In this example the boundary_test table is created with two columns: geotype
defined as a VARCHAR, and g1 defined as the superclass ST_Geometry. The
INSERT statements that follow insert each one of the subclass geometries. The
ST_Boundary() function retrieves the boundary of each subclass stored in the g1
geometry column. Note that the dimension of the resulting geometry is always one
less than the input geometry. Points and multipoints always result in a boundary
that is an empty geometry, dimension -1. Linestrings and multilinestrings return a
multipoint boundary, dimension 0. A polygon or multipolygon always returns a
multilinestring boundary, dimension 1:
CREATE TABLE boundary_test (geotype varchar(20),
g1
ST_Geometry);
INSERT INTO boundary_test VALUES(
'Point', ST_PointFromText('point (10.02 20.01)',1000)
);
INSERT INTO boundary_test VALUES(
'Linestring',
ST_LineFromText('linestring (10.02 20.01,10.32 23.98,11.92 25.64)',1000)
);
INSERT INTO boundary_test VALUES(
'Polygon',
ST_PolyFromText('polygon ((10.02 20.01,11.92 35.64,25.02 34.15,19.15
33.94, 10.02 20.01))',1000)
);
INSERT INTO boundary_test VALUES(
'Multipoint',
ST_MPointFromText('multipoint (10.02 20.01,10.32 23.98,11.92 25.64)',1000)
);
INSERT INTO boundary_test VALUES(
'Multilinestring',
ST_MLineFromText('multilinestring ((10.02 20.01,10.32 23.98,11.92 25.64),
(9.55 23.75,15.36 30.11))',1000)
);
INSERT INTO boundary_test VALUES(
'Multipolygon',
ST_MPolyFromText('multipolygon (((10.02 20.01,11.92 35.64,25.02
34.15,19.15 33.94,10.02 20.01)),((51.71 21.73,73.36 27.04,71.52 32.87,52.43
31.90,51.71 21.73)))',1000)
);
SELECT geotype, ST_Boundary(g1)
FROM boundary_test;
geotype
Point
(expression) 1000 POINT EMPTY
8-20
IBM Informix Spatial DataBlade Module User’s Guide