[postgis-users] how to select points outside polygons?

[Stephen Woodbridge]

Did you try:

select powerplants.gid, plantname
   from powerplants, pca_huc
  where state = 'CA'
        AND NOT st_contains(pca_huc.geom,powerplants.geom)
  order by powerplants.gid;

This should give you all power plants in CA and not in your contains 
clause. What is the coverage of pca_huc table? If this covers all of CA 
then there is not possible result. The would be like say where a=1 and 
not a=1.

-Steve W

On 9/29/2011 1:21 PM, Vishal Mehta wrote:
> I have a point layer and a polygon layer. How do I select points that
> are NOT contained within polygons?
>
> For example, this query correctly selects points contained by polygons
>
> --
>
> select powerplants.gid, plantname
>
> from powerplants, pca_huc
>
> where state = 'CA'
>
> AND
>
> st_contains(pca_huc.geom,powerplants.geom)
>
> order by powerplants.gid;
>
> --
>
> I tried to get the inverse selection using st_disjoint instead of
> st_contains , but that did not work. I also tried using NOT and EXCEPT
> without success (although I may not have constructed the latter queries
> correctly..)
>
> Thanks!
>
> Vishal
>
> //
>
> //
>
>
>
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