定义
ST_ConvexHull 返回 ST_Geometry 对象的凸包。
语法
Oracle 和 PostgreSQL
sde.st_convexhull (geometry1 sde.st_geometry)
SQLite
st_convexhull (geometry1 geometryblob)
返回类型
Oracle 和 PostgreSQL
ST_Geometry
SQLite
Geometryblob
示例
这些示例创建 sample_geometries 表,其中包含三列:id、spatial type 和 geometry。Spatial type 列为 varchar(18) 类型,用于存储 geometry 列中存储的几何子类的名称。表中会插入三种要素:线、面及多点。
针对该表执行的 SELECT 语句返回各子类几何的凸包。
Oracle
--Create table and insert three sample geometries.
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)', 4326)
);
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))', 4326)
);
INSERT INTO sample_geometries (id, spatial_type, geometry) VALUES (
3,
'ST_MultiPoint',
sde.st_geometry ('multipoint (20 20, 30 30, 20 40, 30 50)', 4326)
);
--Find the convex hull of each geometry subtype.
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
--Create table and insert three sample geometries.
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)', 4326)
);
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))', 4326)
);
INSERT INTO sample_geometries (id, spatial_type, geometry) VALUES (
3,
'ST_MultiPoint',
sde.st_geometry ('multipoint (20 20, 30 30, 20 40, 30 50)', 4326)
);
--Find the convex hull of each geometry subtype.
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))
SQLite
--Create table and insert three sample geometries.
CREATE TABLE sample_geometries (
id integer primary key autoincrement not null,
spatial_type varchar(18)
);
SELECT AddGeometryColumn(
NULL,
'sample_geometries',
'geometry',
4326,
'geometry',
'xy',
'null'
);
INSERT INTO sample_geometries (spatial_type, geometry) VALUES (
'ST_LineString',
st_geometry ('linestring (20 20, 30 30, 20 40, 30 50)', 4326)
);
INSERT INTO sample_geometries (spatial_type, geometry) VALUES (
'ST_Polygon',
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))', 4326)
);
INSERT INTO sample_geometries (spatial_type, geometry) VALUES (
'ST_MultiPoint',
st_geometry ('multipoint (20 20, 30 30, 20 40, 30 50)', 4326)
);
--Find the convex hull of each geometry subtype.
SELECT id, spatial_type, st_astext (st_convexhull (geometry))
AS 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))