ST_SymmetricDiff

定义

ST_SymmetricDiff 以两个几何对象作为输入参数，并返回由源对象的非公共部分组成的几何对象。

语法

Oracle 和 PostgreSQL

sde.st_symmetricdiff (geometry1 sde.st_geometry, geometry2 sde.st_geometry)

SQLite

st_symmetricdiff (geometry1 geometryblob, geometry2 geometryblob)

返回类型

Oracle 和 PostgreSQL

ST_Geometry

SQLite

Geometryblob

示例

对于特定报表，县政委员必须确定不相交流域和危险污染源半径区域。

流域表包含 id 列以存储流域名称 (wname)，以及形状列以存储流域区域几何。

污染源表在 id 列中存储场地标识，而各场地的实际地理位置存储在场地点列中。

ST_Buffer 函数生成一个环绕危险废弃物场地点的缓冲区域。ST_SymmetricDiff 函数将返回不相交的缓冲危险废弃物场地和流域的面。

对危险废弃物场地与流域的交集取反可生成相交区域的差集。

Oracle

CREATE TABLE watershed (
 id integer,
 wname varchar(40) 
 shape sde.st_geometry
); 

CREATE TABLE plumes (
 id integer,
 site sde.st_geometry
);

INSERT INTO WATERSHED (ID, WNAME, SHAPE) VALUES (
 1,
 'Big River'
 sde.st_geometry ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO WATERSHED (ID, WNAME, SHAPE) VALUES (
 2,
 'Lost Creek'
 sde.st_geometry ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO WATERSHED (ID, WNAME, SHAPE) VALUES (
 3,
 'Szymborska Stream',
 sde.st_geometry ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO PLUMES (ID, SITE) VALUES (
 20,
 sde.st_geometry ('point (60 60)', 4326)
);

INSERT INTO PLUMES (ID, SITE) VALUES (
 21,
 sde.st_geometry ('point (30 30)', 4326)
);

SELECT ws.id WS_ID,
 sde.st_area (sde.st_symmetricdiff (sde.st_buffer (p.site, .1), ws.shape)) AREA_NO_INT
 FROM plumes p, SENSITIVE_AREAS ws
 WHERE p.id = 20;

     SA_ID     AREA_NO_INT

         1     100.031393
         2     400.031393
         3     400.015697

PostgreSQL

CREATE TABLE watershed (
 id serial,
 wname varchar(40) 
 shape sde.st_geometry
); 

CREATE TABLE plumes (
 id serial,
 site sde.st_geometry
);

INSERT INTO watershed (wname, shape) VALUES (
 'Big River'
 sde.st_geometry ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO watershed (wname, shape) VALUES (
 'Lost Creek'
 sde.st_geometry ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO watershed (wname, shape) VALUES (
 'Szymborska Stream',
 sde.st_geometry ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO plumes (site) VALUES (
 20,
 sde.st_geometry ('point (60 60)', 4326)
);

INSERT INTO plumes (site) VALUES (
 21,
 sde.st_geometry ('point (30 30)', 4326)
);

SELECT ws.id AS WS_ID,
 sde.st_area (sde.st_symmetricdiff (sde.st_buffer (p.site, .1), ws.shape)) AS "no intersection"
 FROM plumes p, watershed ws
 WHERE p.id = 20;

    ws_id     no intersection

         1    100.031393502001
         2    400.031393502001
         3    400.01569751

SQLite

CREATE TABLE watershed (
 id integer primary key autoincrement not null,
 wname text(40)
);

SELECT AddGeometryColumn(
 NULL,
 'watershed',
 'shape',
 4326,
 'polygon',
 'xy',
 'null'
);

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

SELECT AddGeometryColumn(
 NULL,
 'plumes',
 'site',
 4326,
 'point',
 'xy',
 'null'
);

INSERT INTO watershed (wname, shape) VALUES (
 'Big River',
 st_geometry ('polygon ((20 30, 30 30, 30 40, 20 40, 20 30))', 4326)
);

INSERT INTO watershed (wname, shape) VALUES (
 'Lost Creek',
 st_geometry ('polygon ((30 30, 30 50, 50 50, 50 30, 30 30))', 4326)
);

INSERT INTO watershed (wname, shape) VALUES (
 'Szymborska Stream',
 st_geometry ('polygon ((40 40, 40 60, 60 60, 60 40, 40 40))', 4326)
);

INSERT INTO plumes (site) VALUES (
 st_geometry ('point (60 60)', 4326)
);

INSERT INTO plumes (site) VALUES (
 st_geometry ('point (30 30)', 4326)
);

SELECT ws.id AS WS_ID,
 st_area (st_symmetricdiff (st_buffer (p.site, .1), ws.shape)) AS "no intersection"
 FROM plumes p, watershed ws
 WHERE p.id = 2;

    WS_ID     no intersection

         1    400.031393502001
         2    100.031393502001
         3    400.01569751