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# ST\_Buffer
<a name="access-graph-opencypher-22-spatial-functions-st-buffer"></a>

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, number_of_segments_per_quarter_circle)
```

**Arguments (引數)**
+ `geom` - 資料類型 GEOMETRY 的值，或評估為 GEOMETRY 類型的表達式。
+ `distance` - DOUBLE PRECISION 資料類型的值，代表緩衝區的距離 （或半徑）。
+ `number_of_segments_per_quarter_circle` - 資料類型 INTEGER 的值 （應大於或等於 0)。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。

**範例**

```
RETURN ST_Buffer(ST_GeomFromText('LINESTRING (1 2,5 2,5 8)'), 2, 4);
POLYGON ((3 4, 3 8, 3.1522409349774265 8.76536686473018,
         3.585786437626905 9.414213562373096, 4.234633135269821 9.847759065022574,
         5 10, 5.765366864730179 9.847759065022574,
         6.414213562373095 9.414213562373096, 6.847759065022574 8.76536686473018,
         7 8, 7 2, 6.847759065022574 1.2346331352698203,
         6.414213562373095 0.5857864376269051, 5.765366864730179 0.1522409349774265,
         5 0, 1 0, 0.2346331352698193 0.152240934977427,
         -0.4142135623730954 0.5857864376269051,
         -0.8477590650225737 1.2346331352698208, -1 2.0000000000000004,
         -0.8477590650225735 2.7653668647301797,
         -0.4142135623730949 3.414213562373095,
         0.2346331352698206 3.8477590650225735, 1 4, 3 4))
```

以下會傳回近似圓的輸入點幾何緩衝區。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。

```
RETURN ST_Buffer(ST_GeomFromText('POINT (1 1)'), 1.0, 8));
POLYGON ((2 1, 1.9807852804032304 0.8049096779838718,
     1.9238795325112867 0.6173165676349102, 1.8314696123025453 0.4444297669803978,
     1.7071067811865475 0.2928932188134525, 1.5555702330196022 0.1685303876974548,
     1.3826834323650898 0.0761204674887133, 1.1950903220161284 0.0192147195967696,
     1 0, 0.8049096779838718 0.0192147195967696, 0.6173165676349103 0.0761204674887133,
    0.444429766980398 0.1685303876974545, 0.2928932188134525 0.2928932188134524,
     0.1685303876974546 0.4444297669803978, 0.0761204674887133 0.6173165676349102,
     0.0192147195967696 0.8049096779838714, 0 0.9999999999999999,
     0.0192147195967696 1.1950903220161284, 0.0761204674887132 1.3826834323650896,
     0.1685303876974545 1.555570233019602, 0.2928932188134523 1.7071067811865475,
     0.4444297669803978 1.8314696123025453, 0.6173165676349097 1.9238795325112865,
     0.8049096779838714 1.9807852804032304, 0.9999999999999998 2,
     1.1950903220161284 1.9807852804032304, 1.38268343236509 1.9238795325112865,
     1.5555702330196017 1.8314696123025453, 1.7071067811865475 1.7071067811865477,
     1.8314696123025453 1.5555702330196022, 1.9238795325112865 1.3826834323650905,
     1.9807852804032304 1.1950903220161286, 2 1))
```