[Qgis-user] using EPSG:1662 transformation

[Michele Beneventi]

Hi Giovanni,
your answer sounds very good.
Both gdalwarp and OGR work fine for me with +towgs84 declaration (like
+towgs84=0,0,0), but in Qgis there isn't the possibility to adjust the
reprojection with that tranformation parameter.

Thank you very much
Michele



On Tue, Jan 18, 2011 at 7:04 PM, Giovanni Manghi
<giovanni.manghi at gmail.com> wrote:
> Hi,
>
> I don't know if it can help, but I usually do Datum transformations (of
> both vectors and rasters) using datum transformation grids and the CLI
> interface (gdalwarp, ogr2ogr) or QGIS.
>
> When defining the -s_srs crs it is needed to add the "+nadgrids"
> parameter and the "+wktext" parameter (the latter should not be
> necessary if you use +towgs84 parameters instead of a grid file).
>
> In the -t_srs crs it is always needed to add a "dummy" +towgs84
> declaration (like +towgs84=0,0,0) otherwise the transformation will not
> work. This is true for both the grid transformations (using +nadgrids in
> s_srs) and transformations using +towgs84=... (in s_srs).
>
> In QGIS at the moment this means creating two custom CRSs.
>
> In QGIS, the "warp" interface as long as the interfaces that allow to
> save a vector in a new projection, should soon alloow to choose/add
> +towgs84 parameters or transformation grids "on the fly" in order to
> avoid the user to create custom CRSs.
>
> cheers
>
> -- Giovanni --
>
>
>
>
> On Fri, 2011-01-14 at 16:58 +0100, Michele Beneventi wrote:
>> Hi all,
>> I'm using Qgis 1.6 release on windows xp pro 64-bit and in particulary
>> "export to new projection" (ftools).
>>
>> I need to reprojct a layer from WGS84 / UTM zone 32N (EPSG:32632) to
>> Monte Mario / Italy zone 1 (EPSG:3003) with  the transformation 1662
>> (EPSG code).
>> I try to insert the value of the transformation in "custom CRS" with
>> proj4 syntax (+proj=tmerc +lat_0=0.0 +lon_0=9.0 +k=0.9996
>> +x_0=1500000.0 +y_0=0.0 +ellps=intl +units=m
>> +towgs84=-168.6,-34,38.6,-0.374,-0.679,-1.379,-9.48 +units=m +no_defs)
>> and create a new CRS target, but it seems doesn't work properly..
>>
>> With gdalwarp I can put this value in the "-t_srs" parameter and run
>> the command with execellent results.
>>
>> There is another way to customize the reprojection tool with the value
>> of local parameters?
>>
>> Thanks in advance
>> regards
>>
>> Michele
>> _______________________________________________
>> Qgis-user mailing list
>> Qgis-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/qgis-user
>
>
>