ST_ConvexHull

Définition

ST_ConvexHull renvoie l'enveloppe convexe d'un objet ST_Geometry.

Syntaxe

sde.st_convexhull (g1 sde.st_geometry)

Type de retour

ST_Geometry

Exemple

L'exemple crée la table sample_geometries qui contient trois colonnes : id, spatial type et geometry. Spatial type, au format varchar(18), stocke le nom de la sous-classe de géométrie stockée dans la colonne geometry.

CREATE TABLE sample_geometries (id integer, spatial_type varchar(18), geometry sde.st_geometry);

INSERT INTO sample_geometries (id, spatial_type, geometry) VALUES (
1,
'ST_LineString',
sde.st_geometry ('linestring (20 20, 30 30, 20 40, 30 50)', 0)
);

INSERT INTO sample_geometries (id, spatial_type, geometry) VALUES (
2,
'ST_Polygon',
sde.st_geometry ('polygon ((30 30, 25 35, 15 50, 35 80, 40 85, 80 90, 70 75, 65 70, 55 50, 75 40, 60 30, 30 30))', 0)
);

INSERT INTO sample_geometries (id, spatial_type, geometry) VALUES (
3, 
'ST_MultiPoint',
sde.st_geometry ('multipoint (20 20, 30 30, 20 40, 30 50)', 0)
);

L'instruction SELECT ci-dessous liste le nom de la sous-classe stockée dans la colonne spatial type et l'enveloppe convexe de la géométrie.

Oracle

SELECT id, spatial_type, sde.st_astext (sde.st_convexhull (geometry)) CONVEXHULL
FROM  SAMPLE_GEOMETRIES;

ID    SPATIAL_TYPE       CONVEXHULL

 1    ST_LineString      POLYGON ((20.00000000 40.00000000, 
                           20.00000000 20.00000000, 30.00000000 
                           30.00000000, 30.00000000 50.00000000, 
                           20.00000000 40.00000000)) 

 2    ST_Polygon         POLYGON ((15.00000000 50.00000000, 
                           25.00000000 35.00000000, 30.00000000 
                           30.00000000, 60.00000000 30.00000000,
                           75.00000000 40.00000000, 80.00000000 
                           90.00000000, 40.00000000 85.00000000,
                           35.00000000 80.00000000, 15.00000000 
                           50.00000000))

 3    ST_MultiPoint      POLYGON ((20.00000000 40.00000000, 
                           20.00000000 20.00000000, 30.00000000 
                           30.00000000, 30.00000000 50.00000000, 
                           20.00000000 40.00000000))

PostgreSQL

SELECT id, spatial_type, st_astext (sde.st_convexhull (geometry)) 
AS CONVEXHULL
FROM sample_geometries;

id    spatial_type       convexhull

 1    ST_LineString      POLYGON (( 20 40, 20 20, 30 30, 30 50, 
                           20 40)) 

 2    ST_Polygon         POLYGON (( 15 50, 25 35, 30 30, 60 30,
                           75 40, 80 90, 40 85, 35 80, 15 50))

 3    ST_MultiPoint      POLYGON (( 20 40, 20 20, 30 30, 30 50, 
                           20 40))