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I need to be able to replicate with ogr2ogr a coordinate transformation that was executed in ArcGIS for Desktop.

Both ArcGIS and ogr2ogr are based on EPSG standard definition.

There's not only one way to transform data from a reference system A to a reference system B, but many transformations are possible (T1, T2 ... Tn).

After a lot of reading i understood that EPSG codes define, among many other things, CRS (coordinate reference systems, A and B in the previous example), and possible transformation between them (T1...Tn).

When in gis one performs a coordinate transformation ArcGIS prompts the user with the choice of a transformation. On the other side ogr2ogr simply works specifying the source and destination CRS.

two questions then arise:

  • what kind of transformation does ogr2ogr performs? is it still based on the transformation defined within the epsg standard?
  • Is it possible to force ogr2ogr to use a transformation specified via an epsg code?

please keep in mind that my goal is to replicate a transformation executed in gis (thus identified by an epsg code), with a call to ogr2ogr.

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ogr2ogr provides 3 command line options dealing with coordinate systems

-a_srs srs_def:
    Assign an output SRS
-t_srs srs_def:
    Reproject/transform to this SRS on output
-s_srs srs_def:
    Override source SRS

The one you are looking for it -t_srs to transform, though you may also need -s_srs if your source data does not have it's coordinate system set correctly

To specify a coordinate system by an EPSG code you can use the format EPSG:nnnn

for example to transform a shapefile to EPSG 4326

ogr2ogr -f "ESRI Shapefile" output.shp input.shp -t_srs EPSG:4326 
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