[Qgis-developer] Difference for transform reference system between QGIS and GDAL

[Luiz Motta]

Hi all,

Thank Jürgen for your  explanation about how QGIS set the reference system
from source.

I agreement with André Joost about the user should  select your specific
reference.

The source of my problem is the creating of shapefile by GDAL/OGR.

For creating shapefile, the OGR/GDAL not using  all parameters of reference
system.

I resolve my problem, creating the GML file, in this case, the refefence
system is identical of source.

How suggested Etienne i will raise this issue in gdal-dev list.

If someone want to see the script example:
http://pastebin.com/PbjwdrHR

Regards,
Luiz Motta



2014/1/17 Andre Joost <andre+joost at nurfuerspam.de>

> Am 17.01.2014 11:56, schrieb Luiz Motta:
>
>
>  The question is exact this, why the QGIS read the PRJ and understands the
>> 'towgs84', otherwise, the GDAL don't understands, where , the QGIS use the
>> GDAL/OGR provider ?
>>
>>
> This is an intended behaviour.
>
> Other software (like ESRI) don't write datum shifts in the .prj file, but
> leave it to the end user to select one of the available shifts. QGIS has to
> handle these files correctly, so it looks up the EPSG table and selects the
> best fitting code. If you think it has guessed wrong, you can assign
> another CRS to the layer.
>
> GDAL does no guessing. Unless there are not datum shifts provided on
> source and target CRS (using either +datum, +towgs84 or +nadgrids), it does
> no datum shift at all. You can specify -s_srs to override the source file's
> .prj file with an EPSG code that contains a datum shift. This should bring
> the same result as QGIS does automatically.
>
>
> HTH,
> André Joost
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-- 
Luiz Motta
Analista Ambiental - IBAMA/COTIG
Instituto Brasileiro do Meio Ambiente dos Recursos Naturais - IBAMA
IBAMA - SCEN Trecho 2 - Ed. Sede - Cx. Postal nº 09566
CEP 70818-900 - Brasília-DF
Tel: 61.3316-1807
Skype: ibama_luiz-motta
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