[postgis-users] Intersection - No GID

Marcus C. England marcuscengland at gmail.com
Tue Jun 3 12:34:20 PDT 2008

Thanks, Robert. I thought I read that the newer functions beginning with
"ST_" allow you to simplify the expressions, but I am not sure how. When
you are new to this, I think simpler is better (at least easier to learn!).


Burgholzer,Robert wrote:
> Marcus,
> 1) You could create your table prior to populating it, and include a column that is type "SERIAL", this will create an autogenerated integer identifier that you could name "gid" if you so desired.
> 2) select area2d(Intersection(f.the_geom, c.the_geom)) ...
> NOTE: You will have to convert this area2d result from the units of your map projection into acres
> 3) ST_intersection and intersection are the same, the new (ST_*) naming convention was recently added, for reasons that I do not know but assume that they were good ones.
> HTH,
> Robert
> -----Original Message-----
> From:	postgis-users-bounces at postgis.refractions.net on behalf of Marcus C. England
> Sent:	Tue 6/3/2008 2:57 PM
> To:	PostGIS Users Discussion
> Cc:	
> Subject:	[postgis-users] Intersection - No GID
> Hi all,
> I figured out how to use Intersection and get a resulting table with 
> apparently correct results using the example from the PostGIS website:
> CREATE TABLE new_fields AS
>    Intersection(f.the_geom, c.the_geom) AS the_geom,
>    f.attr1,
>    f.attr2,
>    c.clu_name
>    fields f,
>    clu c
>    f.the_geom && c.the_geom
>  AND
>    Intersects(f.the_geom, c.the_geom)
> However, this example does not create a gid column and I therefore can 
> not view the results in a GIS program. Is there a way to create a gid 
> column after-the-fact?
> Optional questions for those feeling super-helpful:
> (1) How should the above SQL be rewritten to include gid in the 
> resulting table?
> (2) I know that eliminating the first line will simply give me a table 
> spit onto the SQL results in pgAdmin. How do I alter the SQL above to 
> give me the acreages rather then a list of the geometries? I can get the 
> acreages from the table resulting from the above, but I can't figure out 
> how to skip the step of creating a table.
> (3) What is the syntax using ST_Intersection rather than Intersection?
> thanks,
> Marcus
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