ST_CHAIKINSMOOTHING

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功能描述

使用 Chaikin 算法平滑线性或多边形几何体。

语法格式

GEOMETRY ST_CHAIKINSMOOTHING(GEOMETRY geom, INTEGER nIterations = 1, BOOLEAN preserveEndPoints = false);

参数说明

• geom：目标 GEOMETRY 对象；
• nIterations：迭代次数，可选。最大值为 5，默认为 1。
• preserveEndPoints：是否保留端点，只对多边形有意义，可选，默认为 FALSE。

函数返回类型

GEOMETRY 类型

使用说明

1. LINESTRINGS 的端点始终被保留。
2. 每次迭代顶点数量都会加倍，因此结果几何图形的点可能比输入多得多。 要减少点数，请对结果使用简化函数（请参阅 ST_SIMPLIFY、ST_SIMPLIFYPRESERVETOPOLOGY 和 ST_SIMPLIFYVW）。
3. 结果具有 Z 和 M 维度（如果存在）的插值。
4. 该函数支持 3d 并且不会丢失 z-index。

示例

平滑 TRIANGLE（三角形）：

SQL> SELECT ST_AsText(ST_ChaikinSmoothing(geom)) smoothed
     FROM (SELECT  'POLYGON((0 0, 8 8, 0 16, 0 0))'::geometry geom) AS foo;

+-------------------------------------------+
|                 SMOOTHED                  |
+-------------------------------------------+
| POLYGON((2 2,6 6,6 10,2 14,0 12,0 4,2 2)) |
+-------------------------------------------+

(1 row)

3 次迭代平滑 POLYGON：

SQL> SELECT ST_AsText(ST_ChaikinSmoothing(
                 'POLYGON ((20 20, 60 90, 10 150, 100 190, 190 160, 130 120, 190 50, 140 70, 120 10, 90 60, 20 20))',3 ));

+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            EXPR1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| POLYGON((37.5 50.625,42.5 59.375,46.09375 67.96875,48.28125 76.40625,49.0625 84.6875,48.4375 92.8125,46.40625 100.78125,42.96875 108.59375,38.125 116.25,31.875 123.75,27.8125 130.9375,25.9375 137.8125,26.25 144.375,28.75 150.625,33.4375 156.5625,40.3125 162.1875,49.375 167.5,60.625 172.5,71.875 176.40625,83.125 179.21875,94.375 180.9375,105.625 181.5625,116.875 181.09375,128.125 179.53125,139.375 176.875,150.625 173.125,159.53125 169.21875,166.09375 165.15625,170.3125 160.9375,172.1875 156.5625,171.71875 152.03125,168.90625 147.34375,163.75 142.5,156.25 137.5,150.625 132.03125,146.875 126.09375,145 119.6875,145 112.8125,146.875 105.46875,150.625 97.65625,156.25 89.375,163.75 80.625,169.53125 73.28125,173.59375 67.34375,175.9375 62.8125,176.5625 59.6875,175.46875 57.96875,172.65625 57.65625,168.125 58.75,161.875 61.25,156.09375 62.5,150.78125 62.5,145.9375 61.25,141.5625 58.75,137.65625 55,134.21875 50,131.25 43.75,128.75 36.25,126.09375 30.46875,123.28125 26.40625,120.3125 24.0625,117.1875 23.4375,113.90625 24.53125,110.46875 27.34375,106.875 31.875,103.125 38.125,98.75 42.96875,93.75 46.40625,88.125 48.4375,81.875 49.0625,75 48.28125,67.5 46.09375,59.375 42.5,50.625 37.5,43.59375 34.21875,38.28125 32.65625,34.6875 32.8125,32.8125 34.6875,32.65625 38.28125,34.21875 43.59375,37.5 50.625)) |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

(1 row)