[gdal-dev] Forget last message, I mess myself with shortcuts > PROJ8, GDAL, National grids

[Juan Pedro Pérez Alcántara]

Hi all,

I'm at a loss trying to understand the relationship between PROJ8, GDAL,
and how to use TIFF national grids PROJ8 data comes with. So far my
findings are the following.

PROJ8 is installed and cs2cs uses the grid to transform, performing an
extremely accurate shift.

GDAL, compiled on the above PROJ8, when running:

gdaltransform -s_srs epsg:23030 -t_srs epsg:25830

yields less accurate results, hinting the grid is not being used. However:

gdaltransform -s_srs "+proj=utm +zone=30 +ellps=intl +units=m +no_defs
+nadgrids=/usr/local/share/proj/es_ign_SPED2ETV2.tif" -t_srs "+proj=utm
+zone=30 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs"

explicitly detailing the use of the grid, nails it. It would be great,
however, to get these results using the -s_srs epsg:XXXX syntax.

So I would like if anyone can help me in carrying out these options:

- can PROJ be used directly in GDAL using the CRS definitions in it? My
hope is that GDAL, somehow, uses PROJ definitions and uses the grid without
any further config;

- if the above is not possible and/or makes no sense, how can I tweak the
SRS PROJ or WKT definitions in GDAL to use the grid?

Any light you can shed on this will be mostly welcome. Thanks in advance.

---

Juan Pedro Pérez Alcántara

jp.perez.alcantara at gmail.com


---

Juan Pedro Pérez Alcántara

jp.perez.alcantara at gmail.com
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