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Hello,

I'm using a customized projection system that is exported to other official projection (Lambert 93, Lambert zone 2...) and I would like to run these transformation within FME. For ex, here are the steps going from 2154 to my custo projection:

Prime Meridian Paris to Greenwich then:

{LambertConformalConic: a=6378249.2 f=293.4660212936269 lat0=46.799999999999955 lon0=2.337229169999998 k=0.99987742 (inv)}

{GridShiftTransform(NTv2:rgf93_ntf.gsb (Inv))}

{LambertConformalConic: a=6378137 f=298.257222101 lat0=46.49999999999996 lon0=2.999999999999997 k=1 }

{AffineTransform2D(ScaleXY(1,1) Rotate(0) Translate(700000,6600000))}

How to define this in FME?

You should check out this article Adding a Custom Transformation (safe.com)

Yes thanks but what are the matching fields/value?

There are a lot of implications in the parameters you posted.

There might be a custom elipsoid definition followed by a custom datum definition and then a custom transformation via an NTv2 grid.

The grid file appears to correspond to an EPSG 4275 transformation to something. I can't figure to which CRS you are trying to reproject.

I think your transformation is already implemented in either CSMapReprojector or PROJReprojector. You just have to specify the gsb file to use as FME might be missing it.

Hi @relativite1905​,

The rgf93_ntf.gsb grid is included with FME, if you download and install the Reprojection Grid Files from the bottom of https://engage.safe.com/support/downloads/#official. However, there is a little setup required to make use of it:

  • In FME Workbench, pick Tools - FME Options from the top menu bar
  • Select the Coordinate Systems option, then scroll down the Maintain Grid Transformations to find RGF93_to_NTF-G-Grid-ClrkIGN
  • Edit RGF93_to_NTF-G-Grid and click the + button to add a grid file
  • Navigate to C:\\Program Files\\FME\\Reproject\\EsriPEGridData\\ntv2\\france to find the rgf93_ntf.gsb file and select it
  • Set direction to Forward and Type to NTv2
  • Click on the entry above it and then click the '-' button to remove it. This ensures that only the rgf93_ntf.gsb grid will be used.
  • Click OK to save

Now the transformation between the RGF93 and NTF-G-Grid-ClrkIGN datums has been set up. The next step is to use the Create Custom Coordinate System tool to create your coordinate system. Be sure to use the 'Nouvelle Triangulation Francaise, RGF93 Grid files, Clarke IGN' Datum in the definition.

After installing the new coordinate system, you will be able to use the CsmapReprojector to convert from EPSG:2154 to your new coordinate system. Set the source and destination coordinate systems, then click the Geographic Transformation drop-down and pick RGF93_to_NTF-G-Grid-ClrkIGN as the transformation.

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