[postgis-users] Intersection - No GID

Burgholzer,Robert rwburgholzer at deq.virginia.gov
Tue Jun 3 12:06:33 PDT 2008

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.


-----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
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,
   fields f,
   clu c
   f.the_geom && c.the_geom
   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?


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