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Postgis多边形内的随机点

发布于 2024-09-11 18:01:08 字数 45 浏览 1 评论 0原文

如果我在 Postgis 中有一个多边形，我如何找到/计算多边形内的随机点？

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无边思念无边月 2024-09-18 18:01:08

@Mike 引用的链接没有代码，但 Dr.JTS 提供了很好的线索：
“点密度”地图...“本质上，这涉及创建一组位于给定多边形内的 N 个随机放置的点”。函数执行此操作：输入是多边形，输出是随机点。

这些链接具有相同的 SQL/PostGIS 函数 RandomPoint(Geometry)：sorokine 2011 和 osgeo.org/postgis/维基百科。第二个链接 (wiki) 更完整，解释并显示了示例，以及作为问题答案的函数 RandomPointsInPolygon(geometry,integer)。

扩展 solion 以输入“每个区域的点密度”，或点之间的平均距离：

 CREATE OR REPLACE FUNCTION RandomPointsInPolygon(
     geom geometry,                -- the polygon
     avg_dist float DEFAULT 20.0,  -- average of 20 units between points 
     min_pts integer DEFAULT 1,    -- min. of points
     max_pts integer DEFAULT 1000  -- max. of points
 ) RETURNS SETOF geometry AS 
 $
   SELECT CASE WHEN npts=1 THEN ST_Centroid($1) 
               ELSE RandomPointsInPolygon($1,npts) 
          END
   FROM (
     SELECT CASE WHEN d<$3 THEN $3 WHEN d>$4 THEN $4 ELSE d END AS npts
     FROM (SELECT (st_area($1)/(pi()*($2/2.0)^2))::integer AS d) AS t
   ) AS t2;
 $ LANGUAGE SQL;

The link cited by @Mike not have a code, but good clues from Dr.JTS:
"dot-density" maps... "Essentially this involves creating a set of N randomly-placed points which lie within a given polygon". A function do this: the input is the polygon, the output the random points.

These links have the same SQL/PostGIS function RandomPoint(Geometry): sorokine 2011 and osgeo.org/postgis/wiki. The second link (wiki) is more complete, explaning and showing examples, and a function RandomPointsInPolygon(geometry,integer) that is an answer to the problem.

Extending the solion to input "density of points per area", or average distance between points:

 CREATE OR REPLACE FUNCTION RandomPointsInPolygon(
     geom geometry,                -- the polygon
     avg_dist float DEFAULT 20.0,  -- average of 20 units between points 
     min_pts integer DEFAULT 1,    -- min. of points
     max_pts integer DEFAULT 1000  -- max. of points
 ) RETURNS SETOF geometry AS 
 $
   SELECT CASE WHEN npts=1 THEN ST_Centroid($1) 
               ELSE RandomPointsInPolygon($1,npts) 
          END
   FROM (
     SELECT CASE WHEN d<$3 THEN $3 WHEN d>$4 THEN $4 ELSE d END AS npts
     FROM (SELECT (st_area($1)/(pi()*($2/2.0)^2))::integer AS d) AS t
   ) AS t2;
 $ LANGUAGE SQL;

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