[PROJ] Big grid files

[Kristian Evers]

> On 27 Apr 2025, at 14.57, Greg Troxel via PROJ <proj at lists.osgeo.org> wrote:
> 
> Javier Jimenez Shaw via PROJ <proj at lists.osgeo.org> writes:
> 
>> 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.
> 
> It's hard to believe that there is true accuracy to 1 mm; that seems
> state of the art for multi-year observations determining HAE at a
> national reference station.  But it might be nice to numerically match
> NGS tools ~exactly as a check.
> 

That would indeed be nice. Almost required, I’d say. But it sort of seems like
they have produced a grid file with a resolution that is too high. I get the feeling
that some of you are in contact with the americans about this, maybe recommend
them to reduce the resolution a bit. They won’t see much usage if they are
too big too handle. Remember how problematic the Australian GB-sized grid files
were before we found a way to compress them?

/Kristian