[postgis-users] st_transform, irreversible?

[Erik Rehn]

Hello Postgis Users!

This is my first post on this list so I will start by asking
a simple (and probably stupid) question. :)

While using ST_AsKml() to produce an overlay for Google Earth I
noticed that all my geometries where shifted slightly south-east.
I figured this had something to do with the transformation between
the projection that my geometries are stored in (SRID 3021) and WGS84 
(4326) that is outputted by ST_AsKml()

Just to test I ran this:

SELECT ST_AsText(
     ST_Transform(
         ST_Transform(
             ST_GeomFromText('POINT(59 18)',4326),
         3021),
     4326));

I input a point in WGS84 (59,18), transforms it to 3021 and then back to 
WGS84. The result I get is:
POINT(58.8672757036296 18.0394763349359)

Can anyone explain this? Am I missing something regarding ST_Transform()?

Im running Postgis 1.5 on Windows.

Thank you for any help!
/Erik

-- 
Erik Rehn
Slagkryssaren
erik at slagkryssaren.com
www.slagkryssaren.com