[PROJ] Is your the geoid model from your country in PROJ?

[Lesparre, Jochem]

> Are we completely sure that nobody no longer use nl_nsgi_naptrans2018.tif ?
No, but I think there has never been a reason to use nl_nsgi_naptrans2018.tif. The only difference between nl_nsgi_naptrans2018.tif and nl_nsgi_nlgeo2018.tif is the interpolation CRS. In theory somebody could use nl_nsgi_naptrans2018.tif in a PROJ pipeline, e.g.:


cct +proj=pipeline

+step +proj=hgridshift +inv +grids=nl_nsgi_rdtrans2018.tif

+step +proj=vgridshift +grids=nl_nsgi_naptrans2018.tif

+step +proj=sterea +lat_0=52.156160556 +lon_0=5.387638889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel

However, we never published such a PROJ pipeline, since the need for a interpolation CRS other than ETRS89 could always be avoided in a pipeline, e.g.:


cct +proj=pipeline

+step +proj=vgridshift +grids=nl_nsgi_nlgeo2018.tif

+step +proj=hgridshift +inv +grids=nl_nsgi_rdtrans2018.tif

+step +proj=sterea +lat_0=52.156160556 +lon_0=5.387638889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel

The only reason we created nl_nsgi_naptrans2018.gtx is that PROJ4-style strings in older PROJ versions (that did not yet support GeoTIFF) needed it:

+proj=sterea +lat_0=52.156160556 +lon_0=5.387638889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +nadgrids=nl_nsgi_rdtrans2018.gsb +wktext +geoidgrids=nl_nsgi_naptrans2018.gtx +no_defs

With PROJ 6 and newer this grid is no longer needed for PROJ4-style strings either:

+proj=sterea +lat_0=52.156160556 +lon_0=5.387638889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +nadgrids=nl_nsgi_rdtrans2018.tif +geoidgrids=nl_nsgi_nlgeo2018.tif +geoid_crs=WGS84 +type=crs

So the conversion from VDatum (.gtx) to GeoTIFF (.tif) was never needed for nl_nsgi_naptrans2018.gtx, but should we keep it now is there?

Jochem



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