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ST_Buffer
ST_Buffer 傳回 2D 幾何,該幾何表示與投影在 xy 笛卡爾平面上的輸入幾何的距離小於或等於輸入距離的所有點。
語法
ST_Buffer(geom, distance)
ST_Buffer(geom, distance, number_of_segments_per_quarter_circle)
引數
- geom
-
GEOMETRY
資料類型的值,或是評估為GEOMETRY
類型的表達式。 - distance
-
DOUBLE PRECISION
資料類型的值,表示緩衝區的距離 (或半徑)。 - number_of_segments_per_quarter_circle
-
INTEGER
資料類型的值。此值決定了圍繞輸入幾何的每個頂點近似四分之一圓的點數。負值預設為零。預設值為 8。
傳回類型
GEOMETRY
ST_Buffer 函數會傳回 xy 笛卡爾平面中的二維 (2D) 幾何。
如果 geom 是 GEOMETRYCOLLECTION
,則會傳回錯誤。
範例
以下 SQL 會傳回輸入 linestring 的緩衝區。
SELECT ST_AsEwkt(ST_Buffer(ST_GeomFromText('LINESTRING(1 2,5 2,5 8)'), 2));
st_asewkt
POLYGON((-1 2,-0.96157056080646 2.39018064403226,-0.847759065022573 2.76536686473018,-0.662939224605089 3.11114046603921,-0.414213562373093 3.4142135623731,-0.111140466039201 3.66293922460509,0.234633135269824 3.84775906502257,0.609819355967748 3.96157056080646,1 4,3 4,3 8,3.03842943919354 8.39018064403226,3.15224093497743 8.76536686473018,3.33706077539491 9.11114046603921,3.58578643762691 9.4142135623731,3.8888595339608 9.66293922460509,4.23463313526982 9.84775906502257,4.60981935596775 9.96157056080646,5 10,5.39018064403226 9.96157056080646,5.76536686473018 9.84775906502257,6.11114046603921 9.66293922460509,6.4142135623731 9.41421356237309,6.66293922460509 9.1111404660392,6.84775906502258 8.76536686473017,6.96157056080646 8.39018064403225,7 8,7 2,6.96157056080646 1.60981935596774,6.84775906502257 1.23463313526982,6.66293922460509 0.888859533960796,6.41421356237309 0.585786437626905,6.1111404660392 0.33706077539491,5.76536686473018 0.152240934977427,5.39018064403226 0.0384294391935391,5 0,1 0,0.609819355967744 0.0384294391935391,0.234633135269821 0.152240934977427,-0.111140466039204 0.337060775394909,-0.414213562373095 0.585786437626905,-0.662939224605091 0.888859533960796,-0.847759065022574 1.23463313526982,-0.961570560806461 1.60981935596774,-1 2))
以下 SQL 會傳回近似於圓的輸入點幾何圖形的緩衝區。由於此命令未指定每四分之一圓的線段數,因此函數使用八個線段的預設值來近似四分之一圓。
SELECT ST_AsEwkt(ST_Buffer(ST_GeomFromText('POINT(3 4)'), 2));
st_asewkt
POLYGON((1 4,1.03842943919354 4.39018064403226,1.15224093497743 4.76536686473018,1.33706077539491 5.11114046603921,1.58578643762691 5.4142135623731,1.8888595339608 5.66293922460509,2.23463313526982 5.84775906502257,2.60981935596775 5.96157056080646,3 6,3.39018064403226 5.96157056080646,3.76536686473019 5.84775906502257,4.11114046603921 5.66293922460509,4.4142135623731 5.41421356237309,4.66293922460509 5.1111404660392,4.84775906502258 4.76536686473017,4.96157056080646 4.39018064403225,5 4,4.96157056080646 3.60981935596774,4.84775906502257 3.23463313526982,4.66293922460509 2.8888595339608,4.41421356237309 2.58578643762691,4.1111404660392 2.33706077539491,3.76536686473018 2.15224093497743,3.39018064403226 2.03842943919354,3 2,2.60981935596774 2.03842943919354,2.23463313526982 2.15224093497743,1.8888595339608 2.33706077539491,1.58578643762691 2.58578643762691,1.33706077539491 2.8888595339608,1.15224093497743 3.23463313526982,1.03842943919354 3.60981935596774,1 4))
以下 SQL 會傳回近似於圓的輸入點幾何圖形的緩衝區。由於此命令指定 3 作為每四分之一圓的線段數,因此函數使用三個線段來近似四分之一圓。
SELECT ST_AsEwkt(ST_Buffer(ST_GeomFromText('POINT(3 4)'), 2, 3));
st_asewkt
POLYGON((1 4,1.26794919243112 5,2 5.73205080756888,3 6,4 5.73205080756888,4.73205080756888 5,5 4,4.73205080756888 3,4 2.26794919243112,3 2,2 2.26794919243112,1.26794919243112 3,1 4))