Sql的MakeValid与道格拉斯普克算法对比

本文主要是介绍Sql的MakeValid与道格拉斯普克算法对比，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Sql Server 的MakeValid

用途

主要用于对不符合地理实例的的空间对象或地理对象进行修正，有时会伴随着类型的变换。

示例

修改前

WKT：

POLYGON ((
108.624008 22.121124, 108.624001 22.121117, 108.623993 22.121109, 108.623993 22.121098,
108.623993 22.121084,
108.624008 22.121075, 108.624016 22.121065, 108.624023 22.121056, 108.624031 22.121046,
108.624039 22.121035,
108.624046 22.121023, 108.624054 22.121014, 108.624062 22.121004, 108.624077 22.120998,
108.624084 22.121,
108.624092 22.121008, 108.6241 22.121016, 108.624115 22.121021, 108.624123 22.121027,
108.62413 22.121033,
108.624146 22.121038, 108.624153 22.121046, 108.624161 22.12105, 108.624168 22.121052,
108.624176 22.121056,
108.624184 22.121061, 108.624184 22.121071, 108.624176 22.121077, 108.624168 22.12108,
108.624161 22.12109,
108.624153 22.121094, 108.624146 22.121105, 108.62413 22.121115, 108.624123 22.121124,
108.624123 22.12113,
108.624115 22.121138, 108.624107 22.121145, 108.6241 22.121155, 108.624092 22.121162,
108.624084 22.121168,
108.624069 22.121172, 108.624054 22.121168, 108.624054 22.121159, 108.624046 22.121149,
108.624039 22.12114,
108.624023 22.121132, 108.624023 22.121126, 108.624016 22.121124, 108.624016 22.12112,
108.624008 22.121119,
108.624008 22.121115, 108.624008 22.121124))

图形显示：

面积：0.31077113673110934 亩

修改后：

WKT：

POLYGON ((
108.624077000015 22.1209980000276, 108.62408400001 22.1209999999846,
108.624092000013 22.1210079999873, 108.624100000015 22.12101599999,
108.624115000013 22.1210210000281,
108.624123000016 22.1210270000156, 108.624130000011 22.1210330000031,
108.624146000016 22.1210379999829, 108.624153000012 22.1210459999857,
108.624161000014 22.1210500000161,
108.624168000009 22.1210519999731, 108.624176000012 22.1210560000036,
108.624184000015 22.1210609999835, 108.624184000015 22.1210710000014,
108.624176000012 22.1210769999889,
108.624168000009 22.1210800000117, 108.624161000014 22.1210899999714,
108.624153000012 22.1210940000019, 108.624146000016 22.1211050000275,
108.624130000011 22.1211149999872,
108.624123000016 22.1211239999975, 108.624123000016 22.121129999985,
108.624115000013 22.1211379999877, 108.624107000011 22.1211449999828,
108.624100000015 22.1211550000007,
108.624092000013 22.1211619999958, 108.62408400001 22.1211679999833,
108.624069000012 22.1211720000138, 108.624054000014 22.1211679999833,
108.624054000014 22.121158999973,
108.624046000012 22.1211490000132, 108.624039000017 22.1211400000029,
108.624023000011 22.1211320000002, 108.624023000011 22.1211260000127,
108.624016000016 22.1211239999975,
108.624016000016 22.1211200000253, 108.624008000013 22.1211190000176,
108.624008000013 22.1211239999975, 108.624001000018 22.1211170000024,
108.623993000016 22.1211089999997,
108.623993000016 22.1210979999742, 108.623993000016 22.121083999984,
108.624008000013 22.1210749999736, 108.624016000016 22.1210650000139,
108.624023000011 22.1210560000036,
108.624031000014 22.1210459999857, 108.624039000017 22.1210350000183,
108.624046000012 22.1210229999851, 108.624054000014 22.1210139999748,
108.624062000017 22.1210040000151,
108.624077000015 22.1209980000276))

图形显示：

面积：0.3107711356846611 亩

对比：可以看出图形经过修整，原本的重合线段已经抹去，但从坐标点的数值可以看出，坐标点有着轻微的移动。同时，经过面积的对比，也可看出面积上也有些许不同，至于能不能
达到精度，就见仁见智了。

道格拉斯普克（以openlayer为例）

用途

主要通过算法来减少冗余点，以方便加载。

原理

通过ABC三点，头尾连成线段，求中间点C到线段的垂线距离有没有超过自行设定的阈值，有则去掉C，没有则保留。

openlayer方法

主要用geometry下的simplify方法生成。

示例

WKT：

POLYGON ((107.8292574 22.8128866, 107.8293028 22.8129182, 107.8294356 22.8130177, 107.8295185 22.8130742, 107.8295963 22.8131402,107.8296349 22.8131766, 107.8296503 22.81319, 107.8296684 22.8132005, 107.8296777 22.8132041, 107.8296523 22.8132306, 107.8296389 22.8132449,107.8296216 22.8132589, 107.8296114 22.8132343, 107.8295876 22.8131918, 107.829567 22.8131709, 107.8295187 22.8131386, 107.8294279 22.813071,107.8293661 22.8130339, 107.8292824 22.8129801, 107.8292573 22.8129591, 107.8292406 22.8129352, 107.8292381 22.8129239, 107.8292374 22.8129042,107.8292384 22.8128895, 107.8292399 22.8128832, 107.8292425 22.8128813, 107.8292461 22.8128818, 107.8292574 22.8128866))