[gdal-dev] Geocentric 9603

[mario santos serrano]

----I HAVE OBTAINED THE SOLUTION----
Hello everybody:

I had one problem (read below) with a Geographic Transformation. I tried multiple choices but anything worked.

I thought that I get the solution when tried this way: 
ogr2ogr -s_srs "+proj=utm +zone=30 +ellpse=intl +towgs84=-84,-107,-120,5,6,3,18 +units=m +no_defs +wktext" -t_srs EPSG:3035 OUT.shp IN.shp
but the adjustment between SHP and the map was still wrong. I get the Seven-parameter transformation from: http://www.colorado.edu/geography/gcraft/notes/datum/datum_f.html

Ultimately I read some advice and I tried a grid:
ogr2ogr -s_srs "+init=epsg:23030 +nadgrids=./PENR2009.gsb +wktext" -t_srs EPSG:3035 OUT.shp IN.shp
This grid are in NTV2 format and contains the longitude and latitude increase between ED50 and ETRS89 datums.

I get this grid from: http://www.ign.es/ign/layoutIn/herramientas.do

Thank you everybody for your advice. Hope this helps.







----INITIAL PROBLEM----




Hello everyone!!

I converted a DXF file to a shapefile using 'ogr2ogr' command. When I use the "-t_srs" parameter the system tells me: "Can't transform coordinates, source layer has no coordinate system. Use -s_srs to set one."

The command '-s_srs' override source SRS.  What is the difference between '-s_srs' and '-a_srs' command? What is the exact meaning of "Assign an output SRS"? I don't understand that.

I use the '-s_srs' command and when I overlay the shapefile over a map,the adjustment isn´t very good with the map, so I must make a geographic transformation. I get that transformation thanks to 'ProjectionUtility' (ArcView). Its name is Geocentric[9603], ED_1950_TO_WGS_1984_13, POSC Code:8045.

I need to make this transformation automatically. How can I make this transformation using 'ogr2ogr'? Is it possible?

Thank you very much

 		 	   		  
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