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

[Luiz Motta]

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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