[postgis-users] SRID confusion

[pcreso at pcreso.com]

Hi Regina...

To add to my confusion:

I'm using AsText, as in the original example below.

If I try to open this multipolygon with QGIS (v1 pre or v0.11) it crashes.

However:

If I do the following in a shell script:

GEOM=`psql -d $DB -Atc "select astext(hole) from hole_multi;"`
GEOM=`echo "$GEOM" | sed 's/SRID=0;//g'`
psql -d $DB -c "update hole_multi set hole=geometryfromtext('$GEOM',4326);"

ie: remove any internal reference to the SRID & update the geomtery value from the revised text string, then everything works perfectly.

Is this a bug in how geomunion() write the geometry? Does it include the constituent SRID's when it shouldn't?


Thanks

   Brent


--- On Fri, 10/31/08, Paragon Corporation <lr at pcorp.us> wrote:

> From: Paragon Corporation <lr at pcorp.us>
> Subject: RE: [postgis-users] SRID confusion
> To: "'PostGIS Users Discussion'" <postgis-users at postgis.refractions.net>
> Date: Friday, October 31, 2008, 10:14 AM
> Brent,
> 
> Are you using AsText or ST_AsEWKT.
> 
> AsText to my knowledges doesn't output SRID so it would
> always be 0.
> 
> Hope that helps,
> Regina 
> 
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On
> Behalf Of
> pcreso at pcreso.com
> Sent: Thursday, October 30, 2008 4:53 PM
> To: postgis-users at postgis.refractions.net
> Subject: [postgis-users] SRID confusion
> 
> Hi guys, 
> 
> I'm not sure what is going on here:
> 
> I am working with some strata boundaries for a fisheries
> survey, mostly
> depth based strata. SRID=4326
> 
> I also have some polygons of areas of untrawlable seabed
> & want to generate
> these cropped by stratum. SRID=4326
> 
> Aas a step in this process I create a new table with a
> single multipolygon
> comprising the geomunion of all the hole polygons.
> SRID=4326
> 
> insert into hole_multi
>                 select 1, geomunion(geom) from holes;
> 
> 
> If I run a query on this table:
> 
> select srid(hole), astext(hole) from hole_multi;
> 
> I get:
> 
>  4326 | MULTIPOLYGON(SRID=0;((55.78 ....
> 
> 
> So the SRID of the column is 4326, but each constituent
> polygon of the
> multipolygon, despite coming from a 4326 dataset, seems to
> be set internally
> to SRID=0.
> 
> The result is the same with:
>  insert into hole_multi
>                 select 1, setsrid(geomunion(geom),4326)
> from holes;
> 
> 
> Any ideas?
> 
> 
> Thanks,
> 
>    Brent Wood
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