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

[Etienne Tourigny]

Hi, you should probably raise this on the gdal-dev mailing list...


On Fri, Jan 17, 2014 at 8:56 AM, Luiz Motta <motta.luiz at gmail.com> wrote:

> Andre,
>
> Thank for quickly response.
>
> 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 ?
>
> File PRJ:
>
> PROJCS["SAD69_UTM_zone_21S",GEOGCS["GCS_SAD69",DATUM["D_South_American_1969",SPHEROID["GRS_1967_Truncated",6378160,298.249999999996]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-57],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",10000000],UNIT["Meter",1]]
>
> Proj4 for QGIS:
> +proj=utm +zone=21 +south +ellps=aust_SA +towgs84=-57,1,-41,0,0,0,0
> +units=m +no_defs
>
> Proj4 for GDAL:
> +proj=utm +zone=21 +south +ellps=aust_SA +units=m +no_defs
>
> Regards,
> Luiz Motta
>
>
> 2014/1/17 Andre Joost <andre+joost at nurfuerspam.de>
>
>> Am 17.01.2014 03:01, schrieb Luiz Motta:
>>
>>  Hi all,
>>>
>>> I had differences for transform the reference system of geometries
>>> between
>>> GDAL and QGIS.
>>>
>>> I made the transform using GDAL into geometry with reference system  SAD
>>> 69
>>> UTM (EPSG 29191) to WGS 84 (EPSG 4326) .
>>>
>>> When i add in QGIS the geometries with WGS84 and SAD 69  using 'on the
>>> fly'
>>> (WGS84), has diferences positions of coordinate (see picture).
>>>
>>> The QGIS reads the reference system of shapefile different than GDAL (see
>>> layer property).
>>>
>>> I would like understand how using GDAL for transform geometries this
>>> reference system of this shapefile ?
>>>
>>> How can difference reading shapefile by QGIS and GDAL ?
>>>
>>
>> The shapefiles .prj file has no +towgs84 parameters, so GDAL sets them to
>> zero.
>>
>> QGIS assigns the EPSG:29191 to the file, which has +towgs84 parameters.
>>
>> 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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