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 <[email protected]> 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 >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/qgis-user > > > _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
