id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,must_fix,platform,platform_version,status_info 2913,"add support for ntv2 grids and +towgs84 parameters in the ""save as..."" dialogs",lutra,nobody,"QGIS is great because offer many ways/tools to save copies of vectors and change their projection along the process. But what about if you want to do the following (example)? {{{ ogr2ogr -f ""ESRI Shapefile"" -s_srs ""+proj=tmerc +lat_0=39.66666666666666 +lon_0=-8.131906111111112 +k=1 +x_0=200000 +y_0=300000 +ellps=intl +units=m +towgs84=-282.1,-72.2,119.95,-1.53,0.14,-0.89,-4.5"" -t_srs ""+proj=tmerc +lat_0=39.6682583333474 +lon_0=-8.133108333465099 +k=1 +x_0=0 +y_0=0 +ellps=GRS80 +towgs84=0,0,0 +units=m +no_defs"" test.shp acid.shp }}} The problem is that there is no interface in QGIS that allows you to define manually the ""-s srs"" or ""-t srs"" parameters (just for vectors, because the ""gdal tools"" tools do allow you to do so). You may think ""so, what is the deal?"". [[BR]] The other problem is that QGIS does not allow either to choose/define the ""+towgs84"" or ""+nadgrids"" parameters so to make things work you will basically have to: *) define a custom CRS, probably a clone of one already available but with the necessary ""+towgs84"" or ""+nadgrids"" parameters. *) save a copy of your vector giving to him the custom CRS with ""+towgs84"" or ""+nadgrids"" parameters *) save this vector in a new one with the -t srs coordinate system This is not really straightforward, but it works. So maybe until things will remain this way it would be useful to document this steps. [[BR]] The proposed ogr2ogr interface would be a very simple ""plugin"", and as a starting point you may want to have a look to the warp tool in the gdal tools plugin. Basically what is needed is a GUI that allows to: *) choose the input vector *) choose the output vector *) choose the input srs *) choose the output srs AND, if necessary *) choose/define +towgs84/+nadgrids parameters [[BR]] A few important notes: *) when the -t srs is a projected one, it must be defined with a ""+towgs84=0,0,0"" parameter, otherwise ogr2ogr will ignore the -s srs +towgs84/+nadgrids parameters. This is important because actually in QGIS you need ALSO to define a custom CRS (for the -t srs parameter) that holds the ""+towgs84=0,0,0"" string. *) NTV2 grids are pretty much more accurate than towgs84 parameters for large scale areas. Are binary files (*.gsb) and are freely available for many countries. To work with ogr2ogr they need to be copied to the appropriate system directory, under linux is {{{ /usr/share/proj/ }}} once there you can use them like this: {{{ ogr2ogr -f ""ESRI Shapefile"" -s_srs ""+proj=tmerc +lat_0=39.66666666666666 +lon_0=-8.131906111111112 +k=1 +x_0=0 +y_0=0 +ellps=intl +units=m +no_defs +nadgrids=ptLX_e89.gsb +wktext"" -t_srs ""+init=epsg:4326"" area_wgs84.shp area.shp }}} So for this interface I would also suggest a dropdown to show the already available .gsb files, and a way to let the users choose new .gsb files to be copied to the proper system location. [[BR]] Another important note: *) when you use the +nadgrids parameter you must also add the ""+wktext"" one, otherwise ""+nadgrids"" will be ignored/stripped. ",enhancement,closed,major: does not work as expected,Version 1.7.0,Data Provider,Trunk,wontfix,,otto.dassau@…,Yes,All,,0