[postgis-users] Intersection - No GID
robe.dnd at cityofboston.gov
Tue Jun 3 12:31:53 PDT 2008
Just to add to some things that Robert said.
1) You can also add the serial after the fact with a
ALTER TABLE new_fields ADD COLUMN gid serial;
ALTER TABLE new_fields ADD CONSTRAINT pk_new_fields PRIMARY KEY(gid);
3) ST_Intersects is different from Intersects although ST_Intersection
is the same as Intersection. It includes the && operator so you can
leave out the && in it
CREATE TABLE new_fields AS
ST_Intersection(f.the_geom, c.the_geom) AS the_geom,
Hope that hleps,
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Sent: Tuesday, June 03, 2008 3:07 PM
To: marcuscengland at gmail.com; PostGIS Users Discussion; PostGIS Users
Subject: RE: [postgis-users] Intersection - No GID
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.
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
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.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
Optional questions for those feeling super-helpful:
(1) How should the above SQL be rewritten to include gid in the
(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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