[PROJ] Big grid files

[Javier Jimenez Shaw]

What I did is using int16. The max error is 1.2 mm (if I did the maths
correctly). The size with that change is about 24 MB
If anybody wants even more accuracy, they can use int32. The reduction is
smaller, but still less than 100 MB.
(any benefit between uint16 vs int16? the positive and negative ranges are
almost the same, so I do not need offset with int16)

I was just telling it to take into consideration when those files become
official.

On Sun, 27 Apr 2025 at 14:43, Even Rouault <even.rouault at spatialys.com>
wrote:

>
> Le 24/04/2025 à 21:51, Mike Taves via PROJ a écrit :
>
> There is Git Large File Storage (Git LFS), which has a limit of 2GB.
>
> Yes, but there are billing / bandwidth implications. I remember we had it
> enabled, but CI cloning typically exhausted the allowed free bandwidth.
>
> Javier, maybe you can try using gdal_translate -scale X X X X -ot UInt16
> -co COMPRESS=DEFLATE -co TILED=YES -co PREDICTOR=2 with the appropriate
> scaling values ?
>
> Or gdal_translate -co DISCARD_LSB=X -co COMPRESS=DEFLATE -co TILED=YES -co
> PREDICTOR=3  to nullify least signifcant bits of the mantissa.
>
>
>
> On Fri, 25 Apr 2025, 04:37 Javier Jimenez Shaw via PROJ, <
> proj at lists.osgeo.org> wrote:
>
>> Hi
>>
>> I am playing with the new American geoid model SGEOID2022
>>
>> After compressing with this command (can I do it better?)
>> gdal_translate sgeoid2022.tif sgcomp.tif -co COMPRESS=DEFLATE -co
>> TILED=YES -co PREDICTOR=3
>> I get a 110 MB file (and it is only one band. No velocities).
>>
>> GitHub has a limit of 100MB:
>>
>> https://docs.github.com/en/repositories/working-with-files/managing-large-files/about-large-files-on-github
>>
>> Just to let you know.
>>
>> Cheers,
>> Javier.
>> _______________________________________________
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>> PROJ at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/proj
>>
>
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