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I used gdalwarp to convert a raster file in EPSG:4326 to one EPSG:28409 I believe that using this method doesn't apply a full transformation as there is no option to select between the numerous transformation options available for 28409 so the output is shifted from what I am expecting. Does anyone know about this and if there isn't a way to do it using gdalwarp is there a way to do this using another gdal tool?

  • What if you transformed 4326 into one of the transformation options available for 28409, and then converted from there? I would expect a shift if there isn't a transformation that is defined. There is some serious scientific calculations behind transformations. – enolan Jul 25 '18 at 15:01
  • Gdal uses the proj library and the source is available for inspection which will solve your problem – Ian Turton Jul 25 '18 at 15:59
  • As @IanTurton says, there should be a look-up table that maps 28409 to a PROJ string. Check the string for a +TOWGS84 parameter. – mkennedy Jul 25 '18 at 16:48
  • Thanks for the comments ok so I am relatively new to GDAL, how would I write something to identify the LUT its using for 28409 to be run is OSGeo for example? @enolan from what I can see there is no way to easily select a transformation option for a particular projection using GDAL. I am guessing it must be possible but I am afraid I don't know how. What I do know is that I want to use the epsg 1303 transformation of epsg 28409 - how I write that into osgeo is a little beyond me at this stage! – charlieb Jul 26 '18 at 7:26

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