[postgis-users] SRID confusion

[pcreso at pcreso.com]

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