ST_Centroid

定義

ST_Centroid は、ポリゴンまたはマルチポリゴンを入力として、ジオメトリのエンベロープの中心点を返します。つまり、中心点とは、ジオメトリの最小および最大 XY 範囲の中間点です。

構文

Oracle および PostgreSQL

sde.st_centroid (polygon sde.st_geometry)
sde.st_centroid (multipolygon sde.st_geometry)

SQLite

st_centroid (polygon geometryblob)
st_centroid (multipolygon geometryblob)

戻り値のタイプ

ST_Point

例

都市 GIS 技術者は、建物のマルチポリゴンを、建物の密集したグラフィックス内で 1 つのポイントとして表示したいと考えています。建物は、bfp テーブルに格納されています。このテーブルは、各データベースで示すステートメントで作成および入力されます。

Oracle

--Create and populate table
CREATE TABLE bfp (
 building_id integer,
 footprint sde.st_geometry);

INSERT INTO bfp VALUES (
 1,
 sde.st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);

INSERT INTO bfp VALUES (
 2,
 sde.st_polygon ('polygon ((20 0, 30 20, 40 0, 20 0))', 4326)
);

INSERT INTO bfp VALUES (
 3,
 sde.st_polygon ('polygon ((20 30, 25 35, 30 30, 20 30))', 4326)
);

--The ST_Centroid function returns the centroid of each building footprint multipolygon. 
--The ST_AsText function converts each centroid point into a text representation recognized by the application.
SELECT building_id,
 sde.st_astext (sde.st_centroid (footprint)) Centroid
 FROM bfp;

BUILDING_ID                   Centroid

   1                     POINT  (5.00000000 5.00000000)
   2                     POINT  (30.00000000 10.00000000)
   3                     POINT  (25.00000000 32.50000000)

PostgreSQL

--Create and populate table
CREATE TABLE bfp (
 building_id serial,
 footprint sde.st_geometry);

INSERT INTO bfp (footprint) VALUES (
 sde.st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);

INSERT INTO bfp (footprint) VALUES (
 sde.st_polygon ('polygon ((20 0, 30 20, 40 0, 20 0))', 4326)
);

INSERT INTO bfp (footprint) VALUES (
 sde.st_polygon ('polygon ((20 30, 25 35, 30 30, 20 30))', 4326)
);

--The ST_Centroid function returns the centroid of each building footprint multipolygon. 
--The ST_AsText function converts each centroid point into a text representation recognized by the application.
SELECT building_id, sde.st_astext (sde.st_centroid (footprint)) 
 AS centroid
 FROM bfp;

building_id                  centroid

   1                     POINT  (5 5)
   2                     POINT  (30 10)
   3                     POINT  (25 33)

SQLite

--Create table, add geometry column, and populate table
CREATE TABLE bfp (
 building_id integer primary key autoincrement not null
);

SELECT AddGeometryColumn (
 NULL,
 'bfp',
 'footprint',
 4326,
 'polygon',
 'xy',
 'null'
);

INSERT INTO bfp (footprint) VALUES (
 st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);

INSERT INTO bfp (footprint) VALUES (
 st_polygon ('polygon ((20 0, 30 20, 40 0, 20 0))', 4326)
);

INSERT INTO bfp (footprint) VALUES (
 st_polygon ('polygon ((20 30, 25 35, 30 30, 20 30))', 4326)
);

--The ST_Centroid function returns the centroid of each building footprint multipolygon. 
--The ST_AsText function converts each centroid point into a text representation recognized by the application.
SELECT building_id, st_astext (st_centroid (footprint)) 
 AS "centroid"
 FROM bfp;

building_id              centroid

   1                     POINT  (5.00000000 5.00000000)
   2                     POINT  (30.00000000 10.0000000)
   3                     POINT  (25.00000000 32.5000000)