[postgis-devel] Reprojection issues

[Nico Mandery]

Hi Kevin,

I also have no porblems with the query on another machine with nearly 
the same configuration -  so it seems rather unexplainable to me.
I will try to downgrade to an earlier version of libproj and recompile 
postgis as a next step.

thanks,
nico

Kevin Neufeld schrieb:
> I can run your query several times, transforming the point to your 
> supplied 3785 srid, without error. (Pg8.3.3, PGIS 1.3.3, Proj4.4.9)
>
> I'm not sure what to suggest, except remove and cleanup your Proj 
> library and re-install.  Perhaps it's an issue with how the library is 
> getting loaded by Postgres and some funny business with your dynamic 
> linker.
>
> -- Kevin
>
> Mark Cave-Ayland wrote:
>> Nico Mandery wrote:
>>> Hello list,
>>>
>>> I got a problem reprojecting geometries from EPSG:3785 (the Google 
>>> or Web Mercator projection) to WGS84 (EPSG:4236).
>>> For example when I try to transform one point postgis gives me the 
>>> following - correct - result:
>>>
>>> projects=# select 
>>> astext(st_transform(GeomFromText('POINT(879650.162980923 
>>> 6108535.16589579)',3785),4326));
>>>                  astext
>>> ------------------------------------------
>>> POINT(7.90203186083991 48.0100993171653)
>>> (1 row)
>>>
>>> When I try it again with exactly the same query, I get a wrong 
>>> result and an error from libproj:
>>>
>>> projects=# select 
>>> astext(st_transform(GeomFromText('POINT(879650.162980923 
>>> 6108535.16589579)',3785),4326));
>>> WARNING:  transform: -38 (failed to load NAD27-83 correction file)
>>>                      astext
>>> --------------------------------------------------
>>> POINT(1.23892476139034e-06 7.52729195068025e-06)
>>> (1 row)
>>>
>>> Every following query will also return wrong results, until I close 
>>> the connection to the database. The first query after establishing a
>>> new connection to postgresql returns a correct result again, every 
>>> following raises the error again.
>>> The NAD correction files exist. Transforming coordinates with cs2cs 
>>> from libproj works without any problems.
>>>
>>> I tried it with Postgresql 8.2.4 and 8.3.3 and postgis 1.3.2 and 
>>> 1.3.3. The proj4text in spatial_ref_sys for EPSG:3785 is
>>> "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 
>>> +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs"
>>>
>>> Thanks a lot,
>>> Nico
>>
>>
>> Hi Nico,
>>
>> I'm not sure about the +wktext part of your proj4text as I've never 
>> seen that before - so maybe it is an invalid PROJ.4 string? What 
>> happens if you try the transformation using the standard proj 
>> executable?
>>
>>
>> ATB,
>>
>> Mark.
>>
> _______________________________________________
> postgis-devel mailing list
> postgis-devel at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-devel