如何在postgis中将许多点转换为多点

Question

I need to convert a table of points where i have those columns (id,the_geom) to a multipoints?

Why I need to do this? Because I want to create a buffer around each point, and if I work with point i will get one buffer for each point, but what i really nead is on polygone buffer for the whole table. The table countains more than 2000 records.

here is an image illustrating what i need to do (buffering a multi point):

many thanks

Answer 1

您要查找的函数是汇总形式的ST_Union：

SELECT ST_Multi(ST_Union(the_geom)) FROM myTable;

Answer 2

This might just be a display problem, if you are using pgAdmin III to view the query result. It seems that geometries with a large number of records (eg 2000 in this case) won't display in the data output pane.

You could check the result of your query by using:

SELECT ST_AsText(ST_ConcaveHull(ST_Collect(the_geom),0.90)) As cc_hull FROM mytable;

This should return the concave hull polygon as text in the data output pane.

Answer 3

我认为ST_ConvexHull是您想要的。

SELECT ST_Buffer(ST_ConvexHull(ST_Collect(the_geom)),0.01) FROM mytable;