I think what Lucas wants is actually the mirror statement:
UPDATE parcels SET landuse = land_use.type
FROM landuse WHERE
ST_Within(centroid(parcels.the_geom),land_use.the_geom);
-- Andy
On May 30, 2008, at 7:54 AM, Obe, Regina wrote:
Markus,
Rule of thumb for relation operations - I think you always read it A
function_name B
So A within B -> Within(A,B)
I think that holds true for all the spatial relation functions in
PostGIS.
Lucas - Markus gave you the correlated sub query approach. You can
also
do it without a subquery. Which one is faster depends on how big your
data sets are I think. The non-correlated I think generally works
better (especially for large data sets) (make sure to have indexes on
both geom fields).
I think the correlated sub query always forces a nested loop join.
Below is a non-sub query way of doing it. For the new versions of
PostGIS you can also replace the && Within with just ST_Within.
UPDATE land_use SET type = parcels.landuse
FROM parcels
WHERE
ST_Within(centroid(parcels.the_geom),land_use.the_geom);
Hope that helps,
Regina
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Markus Schaber
Sent: Friday, May 30, 2008 7:26 AM
To: postgis-users@postgis.refractions.net
Subject: Re: [postgis-users] Attributes update
Hi, Lucas,
"Lucas Mueller" <[EMAIL PROTECTED]> wrote:
I have two polygon layers (let's say Parcels and Land_use). I would
like to
assign the attribute Land_use.type to the Parcels.landuse column by a
query
that assigns a certain land use type to a parcel if the centroid of
the
parcel is within a certain land use polygon. I hope to be clear
enough...
Any idea on how to proceed?
Try something like:
update land_use set type=(select parcels.landuse FROM parcels where
land_use.the_geom && parcels.the_geom AND
within(centroid(parcels.the_geom),land_use.the_geom));
Btw, I tend to mix up the argument order of within and contains, so
please double-check.
Regards,
Markus
--
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf. | Software Development GIS
Fight against software patents in Europe! www.ffii.org
www.nosoftwarepatents.org
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