ST_PointOnSurface takes an ST_Polygon or ST_MultiPolygon and returns an ST_Point guaranteed to lie on its surface.

Oracle

sde.st_pointonsurface (pl1 sde.st_geometry)
sde.st_pointonsurface (mpl1 sde.st_geometry)

PostgreSQL

st_pointonsurface (pl1 st_geometry)
st_pointonsurface (mpl1 st_geometry)

ST_Point

The city engineer wants to create a label point for each building's footprint. The building footprints are stored in the buildingfootprints table that was created with the following CREATE TABLE statement.

Oracle

CREATE TABLE buildings (building_id integer,
footprint sde.st_geometry);

INSERT INTO buildings (building_id, footprint) VALUES (
1,
sde.st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 0)
);

INSERT INTO buildings (building_id, footprint) VALUES (
2,
sde.st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 0)
);

PostgreSQL

CREATE TABLE buildings (building_id integer,
footprint st_geometry);

INSERT INTO buildings (building_id, footprint) VALUES (
1,
st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 0)
);

INSERT INTO buildings (building_id, footprint) VALUES (
2,
st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 0)
);

The ST_PointOnSurface function generates a point that is guaranteed to be on the surface of the building footprints. The ST_PointOnSurface function returns a point that the ST_AsText function converts to text for use by the application.

Oracle

SELECT sde.st_astext (sde.st_pointonsurface (footprint)) Surface_Points
FROM buildings;

SURFACE_POINTS

POINT  (5.00000000 5.00000000)
POINT  (25.00000000 5.00000000)

PostgreSQL

SELECT st_astext (st_pointonsurface (footprint)) AS Surface_Points
FROM buildings;

surface_points

POINT  (5 5)
POINT  (25 5)