proj-datumgrid git repository

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proj-datumgrid git repository

Sebastiaan Couwenberg
To help create proj-datumgrid distributions (tarballs & zip files) I've
imported the releases since 1.0 into a git repository and added a simple
CMake build system to create the tarballs & zip files from the source
directory.

 http://git.linuxminded.nl/?p=OSGeo/proj-datumgrid

The .lla files were no longer included in 1.6RC1 so I've added the ones
from 1.5 to the lla/ directory. The directory was included in the zip
file but did not contain anything.

nad2bin -f ctable2 ... is used to convert the .lla files as part of the
cmake invocation, and a dist target is added to call the package_source
target for convenience.

Unfortunately the resulting grid shift files are not identical to the
ones included in proj-datumgrid-1.6. I haven't been able to figure out
what causes that difference, the .lla sources may have changed for 1.6
or it may just be some system dependent metadata (timestamp?), or
something else entirely. I need to investigate this more thoroughly.

I would like for the proj-datumgrid project to collect the various
freely redistributable national grid shift files to have these available
out-of-the-box when installing PROJ.4. The biggest hurdle currently is
the tendency to prevent modification of the correction values making the
grids non-free and not suitable for inclusion in Free Software projects.

Does this proj-datumgrid repository look like a viable option to help
maintain the proj-datumgrid releases in the future? If so, I can mirror
it on GitHub where it can be taken over by OSGeo organization.

The work on this repository was triggered by the earlier discussion on
this list about the promotion of proj-datumgrid-1.6.RC1, see:

 http://lists.maptools.org/pipermail/proj/2016-August/007459.html

Kind Regards,

Bas

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Re: proj-datumgrid git repository

Sebastiaan Couwenberg
On 10/29/2016 04:10 PM, Sebastiaan Couwenberg wrote:
> Unfortunately the resulting grid shift files are not identical to the
> ones included in proj-datumgrid-1.6. I haven't been able to figure out
> what causes that difference, the .lla sources may have changed for 1.6
> or it may just be some system dependent metadata (timestamp?), or
> something else entirely. I need to investigate this more thoroughly.

The reason for the non-identical grid shift files is that the nad2bin
output was not reproducible prior to PROJ.4 4.9.3, see:

 https://github.com/OSGeo/proj.4/pull/381

The ID is now zero padded instead of containing random data, and the ID
field is the only difference between the grid shift files in
proj-datumgrids-1.6 and those created from the .lla files included in
1.5 and earlier. See for example the diff for the hexdumps of the null
datum grid.

Kind Regards,

Bas

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