Brent,
Which version of PostGIS are you using? I'm guessing an older version.
If I do this
SELECT AsText('SRID=4326;POLYGON((1 2 3, 4 5 6, 7 8 9, 1 2 3))')
I get this
"POLYGON((1 2,4 5,7 8,1 2))"
Which observe has no SRID information.
If I do this
SELECT AsEWKT('SRID=4326;POLYGON((1 2 3, 4 5 6, 7 8 9, 1 2 3))')
I get
"SRID=4326;POLYGON((1 2 3,4 5 6,7 8 9,1 2 3))"
(which observe maintains the SRID info)
So maybe an earlier version included an SRID which would obviously be 0 or
-1 since it basically throws that information away so is for all intents and
purposes is forced to unknown now.
So I guess my only suggestion - stay away from AsText if you care about SRID
And Use ST_AsEWKT or AsEWKT instead and ST_GeomFromEWKT or GeomFromEWKT.
Hope that helps,
Regina
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
[EMAIL PROTECTED]
Sent: Thursday, October 30, 2008 5:37 PM
To: PostGIS Users Discussion
Subject: RE: [postgis-users] SRID confusion
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 <[EMAIL PROTECTED]> wrote:
> From: Paragon Corporation <[EMAIL PROTECTED]>
> Subject: RE: [postgis-users] SRID confusion
> To: "'PostGIS Users Discussion'"
> <postgis-users@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: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of
> [EMAIL PROTECTED]
> Sent: Thursday, October 30, 2008 4:53 PM
> To: postgis-users@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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