postgresql 如何使用 PostGIS 将多边形数据转换为线段
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How to convert polygon data into line segments using PostGIS
提问by gouse shaik
I have a polygon data table in PostgreSQL/PostGIS. Now I need to convert this Polygon data into its corresponding line segments. Can anybody tell me how to convert it using PostGIS queries.
我在 PostgreSQL/PostGIS 中有一个多边形数据表。现在我需要将此多边形数据转换为其相应的线段。谁能告诉我如何使用 PostGIS 查询转换它。
Thanks in Advance
提前致谢
回答by mloskot
Generally, converting polygon to line may be not straightforward because there is no one-to-one mappingand various elements of polygon map to different linestring (exterior ring, interior rings, etc.).
通常，将多边形转换为线可能并不简单，因为没有一对一映射，并且多边形的各种元素映射到不同的线串（外环、内环等）。
Considering that, you will need to split each of those separately following possible approach like this:
考虑到这一点，您需要按照如下可能的方法分别拆分每个部分：
SELECT ST_AsText( ST_MakeLine(sp,ep) )
FROM
-- extract the endpoints for every 2-point line segment for each linestring
(SELECT
ST_PointN(geom, generate_series(1, ST_NPoints(geom)-1)) as sp,
ST_PointN(geom, generate_series(2, ST_NPoints(geom) )) as ep
FROM
-- extract the individual linestrings
(SELECT (ST_Dump(ST_Boundary(geom))).geom
FROM mypolygontable
) AS linestrings
) AS segments;
depending on what polygon data are stored in mypolygontable, you may want to dump not only the boundary (as above using ST_Boundary) but also other elements. The code above with more detailed overview is taken from the postgis-users list: Split a polygon to N linestrings
根据存储在 中的多边形数据mypolygontable，您可能不仅要转储边界（如上所述使用ST_Boundary），还要转储其他元素。上面有更详细概述的代码取自 postgis-users 列表：Split a polygon to N linestrings
There is also a generic approach to the problem explained in Exploding a linestring or polygon into individual vectors in PostGIS
在 PostGIS 中将线串或多边形分解为单个向量中解释的问题还有一个通用方法
回答by D_C
This is the first hit on google when you search this problem. I don't know if so much time has passed a function has been created since, but for future googlers ST_ExteriorRings(geom) worked great for me. http://postgis.net/docs/ST_ExteriorRing.html
这是您搜索此问题时在 google 上的第一次点击。我不知道从那以后创建的函数是否已经过去了很长时间，但对于未来的 googlers ST_ExteriorRings(geom) 对我来说非常有用。 http://postgis.net/docs/ST_ExteriorRing.html
