[PROJ] Gridshift files

[Javier Jimenez Shaw]

PROJ 9.2.1 has included many grid files, including the ones that you mention
https://github.com/OSGeo/PROJ/blob/master/data/sql/grid_alternatives.sql#L314
https://github.com/OSGeo/PROJ/blob/master/data/sql/grid_alternatives.sql#L144
You can see them all in cdn.proj.org
Check that you have these files included via PROJ-data package (they are
tiff files, properly covered from the original files). Try letting PROJ to
use them automatically, without adding them in the wkt.
To check the transformation used projinfo and cs2cs are good helper tools

By the way, it is strange that using epsg:2207 from Turkey with a grid file
from Spain you can get any meaningful result.

Cheers


On Mon, 25 Sept 2023, 11:56 Mladen Mijatovic via PROJ, <proj at lists.osgeo.org>
wrote:

> Dear,
>
> We are trying to substitute old Proj 5.1 in our project and use new Proj
> 9.2.1.
>
> When crs is defind with proj4string or wkt, we do not have issue with
> transforming coordinates from/to EPSG:4326, except when we are using
> grid files e.g.
>
> +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000
> +datum=OSGB36 +units=m +ellps=airy +no_defs
> +nadgrids=OSTN15_NTv2_OSGBtoETRS.gsb  +type=crs
>
> PROJCS["ED50 / 3-degree Gauss-Kruger zone 10",
>      GEOGCS["ED50",
>          DATUM["European_Datum_1950",
>              SPHEROID["International 1924",6378388,297],
>              EXTENSION["PROJ4_GRIDS","SPED2ETV2.gsb"]],
>          PRIMEM["Greenwich",0,
>              AUTHORITY["EPSG","8901"]],
>          UNIT["degree",0.0174532925199433,
>              AUTHORITY["EPSG","9122"]],
>          AUTHORITY["EPSG","4230"]],
>      PROJECTION["Transverse_Mercator"],
>      PARAMETER["latitude_of_origin",0],
>      PARAMETER["central_meridian",30],
>      PARAMETER["scale_factor",1],
>      PARAMETER["false_easting",10500000],
>      PARAMETER["false_northing",0],
>      UNIT["metre",1,
>          AUTHORITY["EPSG","9001"]],
>      AUTHORITY["EPSG","2207"]]
>
> Conversion fails with (HUGE_VAL, HUGE_VAL) coordinates.
>
> If we allow user to define crs by proj4string or wkt and use gridshift
> files:
>
> - How proj4string/wkt need to looks like?
>
> - What c++ functions we need to call to get these coordinates converted
> without any errors?
>
> Best regards,
> Mladen.
> _______________________________________________
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> PROJ at lists.osgeo.org
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>
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