[postgis-users] Mixing SRID's

[Johan Wehtje]

Markus
Thanks your reply.
Given that I had already implemented a trigger to transform the data entered
at the front end I feel a little foolish for not having thought to take it
that step further. Where I am currently stuck though is in trying to pick
from the 26,761 SRID's available. I have already experienced the glitches
that result from trying to use Projected Geometry ( see an earlier thread on
trying to understand why my Scale's were all wrong), but I remain unclear on
how to pick the SRID I should use as the common standard. Much of my incoing
data is either in the form of shape files  or from Feild surveys conducted
using a Differential or even ordinary GPS. I have tried using SRID 4326, but
I run into the same scale problem i ran into earlier because apparently this
SRID is projected. But when I do a like search on WGS84 I get hundreds of
resuts, and reading the srtext and proj4 feilds to try and figure out which
SRID I should be using is not especially user freindly. Is there somewhere
where I can egt a list of the more common datums that I can check my
database agaoinst.

On 11/25/05, Markus Schaber <schabi at logix-tt.com> wrote:
>
> Hi, Johan,
>
> Johan Wehtje wrote:
> > Is it possible to store geometry with differing SRID's in one table?
> >
> > I want to keep track of a heterogenous collection of Geometry, sometimes
> > loaded from Shapefiles, or from GPS surveys - and would like to know if
> > I have to create a seperate Table for each SRID, or whther I have to
> > somehow convert all the geometry to a single standard.
>
> It is possible, but not OpenGIS standards compliant.
>
> You can simply drop the SRID constraint that was created by
> addGeometryColumn().
>
> Alternatively, you can use a "before insert" and "before update" trigger
> to transparently transform() all input geometries to a common SRID. This
> has the advantage that map display or index searches work better.
>
> If you need both the original data for exact reproduciton and the
> unified ones for efficient processing, you can use two geometry columns
> - the first one contains the original geometries with mixed SRIDs, and
> the second one is automatically populated by transform()ing the first
> one via triggers.
>
> Markus
>
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