ST_Buffer

Definición

ST_Buffer toma un objeto de geometría y distancia, y devuelve un objeto de geometría que es la zona de influencia en torno a objeto de origen.

Sintaxis

Oracle y PostgreSQL

sde.st_buffer (geometry sde.st_geometry, distance double_precision)

SQLite

st_buffer (geometry geometryblob, distance double_precision)
st_buffer (geometry geometryblob, distance double, text unit_name)

Unit_name es la unidad de medida de la distancia de zona de influencia.

Tipo de devolución

Oracle y PostgreSQL

ST_Geometry

SQLite

Geometryblob

Ejemplo

En este ejemplo se crean dos tablas, sensitive_areas y hazardous_sites; rellena las tablas; utiliza ST_Buffer para generar una zona de influencia alrededor de los polígonos en la tabla hazardous_sites; y se encuentra donde las zonas de influencia superpongan los polígonos sensitive_areas.

Oracle

CREATE TABLE sensitive_areas (
 id integer,
 zone sde.st_geometry
); 

CREATE TABLE hazardous_sites (
 site_id integer,
 name varchar(40),
 location sde.st_geometry
); 

INSERT INTO SENSITIVE_AREAS VALUES (
 1,
 sde.st_polygon ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO SENSITIVE_AREAS VALUES (
 2,
 sde.st_polygon ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO SENSITIVE_AREAS VALUES (
3,
sde.st_polygon ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 0)
);

INSERT INTO HAZARDOUS_SITES VALUES (
 102,
 'W. H. KleenareChemical Repository',
 sde.st_pointfromtext ('point (60 60)', 4326) 
); 

SELECT sa.id "Sensitive Areas", hs.name "Hazardous Sites"
 FROM SENSITIVE_AREAS sa, HAZARDOUS_SITES hs
 WHERE sde.st_overlaps (sa.zone, sde.st_buffer (hs.location, .01)) = 1;

PostgreSQL

CREATE TABLE sensitive_areas (
 id serial,
 zone sde.st_geometry
); 

CREATE TABLE hazardous_sites (
 site_id serial,
 name varchar(40),
 location sde.st_geometry
); 

INSERT INTO sensitive_areas (zone) VALUES (
 sde.st_polygon ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO sensitive_areas (zone) VALUES (
 sde.st_polygon ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO sensitive_areas (zone) VALUES (
 sde.st_polygon ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO hazardous_sites (name, location) VALUES (
 'W. H. KleenareChemical Repository',
 sde.st_point ('point (60 60)', 4326) 
); 

SELECT sa.id AS "Sensitive Areas", hs.name AS "Hazardous Sites"
 FROM sensitive_areas sa, hazardous_sites hs
 WHERE sde.st_overlaps (sa.zone, sde.st_buffer (hs.location, .01)) = 't';

Sensitive Areas                Hazardous Sites
             3                W.H. KleenareChemical Repository

SQLite

CREATE TABLE sensitive_areas (
 id integer primary key autoincrement not null
); 

SELECT AddGeometryColumn (
 NULL,
 'sensitive_areas',
 'zone',
 4326,
 'polygon',
 'xy',
 'null'
);

CREATE TABLE hazardous_sites (
 site_id integer primary key autoincrement not null, 
 name varchar(40)
); 

SELECT AddGeometryColumn (
 NULL,
 'hazardous_sites',
 'location',
 4326,
 'point',
 'xy',
 'null'
);

INSERT INTO sensitive_areas (zone) VALUES (
 st_polygon ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO sensitive_areas (zone) VALUES (
 st_polygon ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO sensitive_areas (zone) VALUES (
 st_polygon ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO hazardous_sites (name, location) VALUES (
 'W. H. KleenareChemical Repository',
 st_point ('point (60 60)', 4326) 
); 

SELECT sa.id AS "Sensitive Areas", hs.name AS "Hazardous Sites"
 FROM sensitive_areas sa, hazardous_sites hs
 WHERE st_overlaps (sa.zone, st_buffer (hs.location, .01)) = 1;

Sensitive Areas                Hazardous Sites
             3                W.H. KleenareChemical Repository