PostGIS函数将几何线连接在一起？ [英] PostGIS function to connect geometry LINE together?

问题描述

（注意：the_geom是一个几何值（类型：LINESTRING），在这种情况下，我随机选择它们以供读取）

  gid | kstart |肯德| ctrl_sec_no | the_geom | the_sum_geom 
 626 | 238 | 239 | 120802 | 123456 | NULL 
 638 | 249 | 250 | 120802 | 234567 | NULL 
 4037 | 239 | 249 | 120802 | 345678 | NULL 
  

<实践描述]对于那些不介意这个目的的人来说，可以跳过这个

我想做'this'（来自我过去的问题的一组查询，链接
位于这篇文章的末尾）表B中的每一行（又名
land_inventory）。这两个表格通过'ctrl_sec_no'
（也就是道路的控制部分号码）相关，这意味着::在一个
ctrl_sec_no - 120802（实际上，这是一条相当于3
几何LINESTRINGs（the_geom）连接在一起，从kstart 238（从238公里开始）到kend 250）

[ PostGIS问题]

问题是如何将这3行{aka gid（626,638,4037）从表}连接在一起并导致'the_sum_geom'（最初为NULL）通过使用PostGIS功能（无论）。之后我们将使用这个'the_sum_geom'来找到这个几何体上的POINT LINESTRING

（

解决方案

您正在寻找的功能是

 更新mytable集合rel =nofollow> ST_Union ，您需要使用它： the_sum_geom = 
 ST_LineMerge（（从mytable中选择ST_Union（the_geom），其中ctrl_sec_no = 120802））
其中ctrl_sec_no = 120802; 
  

使用 ST_LineMerge 你可以从Multiline转换为LineString，但是有一个警告，如果多行不能合并，它将返回多行而不做任何修改。请参阅 ST_LineMerge 文档，以了解ST_LineMerge可以或不可以执行的操作。

(note: the_geom is a geometry value (TYPE: LINESTRING), in this case i random them for readability)

gid | kstart  | kend    | ctrl_sec_no | the_geom | the_sum_geom
626 | 238     | 239     | 120802      | 123456   | NULL
638 | 249     | 250     | 120802      | 234567   | NULL
4037| 239     | 249     | 120802      | 345678   | NULL

[Real Practice Description] just skip this for those who don't mind the purpose

I would like to do 'this' (a set of queries from my past question, link located on the end of this post) for every row in Table B (aka. land_inventory). These two tables are related by 'ctrl_sec_no' (aka. control section number of a road) which means :: in ONE ctrl_sec_no -- 120802 (in fact, it is a road which is equivalent to 3 geometry LINESTRINGs (the_geom) connected together, from kstart 238 (start at kilometre of 238) to kend 250)

[PostGIS question]

the question is how to connect this 3 lines {aka gid(626,638,4037) from the table} together and result in 'the_sum_geom' (initially NULL) by using PostGIS functions (whatever). after that we will use this 'the_sum_geom' to find the POINT on this geometry LINESTRING

(How calculate things from many tables by using a few queries?).

解决方案

The function you are looking for is ST_Union, you need to use it with the aggregate form:

update mytable set the_sum_geom = 
ST_LineMerge( ( select ST_Union(the_geom) from mytable where ctrl_sec_no  = 120802 ) )
where ctrl_sec_no = 120802;

With ST_LineMerge you can convert from Multiline to LineString but there is a caveat, if the multi line cant be merged it will return the multiline without any modification. See the ST_LineMerge docs to understand what ST_LineMerge can or can't do.

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