[gdal-dev] Apply Vertical Grid Shift to coordinate

[Matthias Kuhn]

Hi Even,

On Thu, Oct 22, 2020 at 10:41 AM Even Rouault <even.rouault at spatialys.com>
wrote:

> Hi Matthias,
>
> (would be more a topic for proj mailing list)
>

(noticed just after sending, but immediately after figured that the
audience will likely be similar)


> > I am trying to apply a vertical grid shift to a coordinate. I am
> > extrapolating from the example in the documentation at
> > https://proj.org/operations/transformations/vgridshift.html
> >
> > The command I am entering is
> >
> > echo 46.9480 7.4474 590 2020 | cct +proj=vgridshift
> > +grids=./geoid+HTRANS_ETRS2020.gtx
> >
> > the result is:
> >
> >  46.9480000000    7.4474000000          -inf     2020.0000
> >
> > I was hoping for the altitude being corrected by roughly 50 meters
> (instead
> > of being -inf).
>
> If the coordinate is located at Kornhausplatz in Bern, Switzerland, rather
> than at Dollo in Ethiopia, you'd better switch your 2 first figures ;-)
>

Fair point, I am indeed more interested in Bern results than in Ethiopian
results.
Unfortunately The result doesn't change significantly

echo 7.4474 46.9480 590 2020 | cct +proj=vgridshift
+grids=./geoid+HTRANS_ETRS2020.gtx
  7.4474000000   46.9480000000          -inf     2020.0000


>
> When using PROJ pipelines, the coordinate order is longitude,latitude /
> easting,northing , unless there are +proj=axisswap operations changing
> that.
> When using higher level PROJ interfaces like cs2cs or projinfo with EPSG
> code,
> then you'll have to comply with EPSG axis order.
>

Thanks for the context, good to know !
Matthias


>
> Even
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
>
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