[PROJ] Proposal for a geodetic deformation model format

[Martin Desruisseaux]

Hello Chris

Thanks for your reply.

Le 05/12/2019 à 19:00, Chris Crook a écrit :

> As you rightly say there is also a lot value in a standardisation 
> process with OGC, though of course that is a (much much) longer process.
>
Just for information, from the presentation we had at OGC, it seems that 
ESRI wants to go relatively fast too (1~3 years in my understanding).


> On HDF5 vs GeoTIFF.. As you rightly say apart from some details this 
> proposal is largely format agnostic. I know the ESRI GGXF initiative 
> is now proposing using HDF5, and certainly that could serve as well.
>
A possible approach could be to put table(s) mapping the document 
attributes to CF-Conventions attributes when a match exists (i.e. to 
draft what it would looks like if the data were in a HDF5 file). It may 
help to compare the formats. But I realize that it would require more 
work, this is not a request.


> Curiously I did propose HDF5 as an option for deformation models a 
> while ago, but at that time there wasn't much appetite for using it as 
> (IIRC) it wasn't so well suited to deploying with online web services.
>
Its seems that HDF5 viewers exist in JavaScript since 2016 [1], and 
other readers are yet more recent [2]. Maybe they were missing at time 
of your proposal. But I admit that HDF5 support in browsers is not as 
old as GeoTIFF supports.


> (…snip…) I found as I was developing this proposal that there seemed 
> to be more advantages to a multiple file implementation. Because 
> GeoTIFF provides the nested grid capability the number of files is not 
> excessive (unlike the LINZ publication format as individual grids). 
> One advantage is that different versions of the deformation model will 
> only differ in a few of the component files. Most would be common to 
> the versions, so using a multiple file implementation allows these to 
> be shared.
>
Thanks for the insight. Together with Even questions in his previous 
email it help me to understand better.

     Regards,

         Martin

[1] https://github.com/HDF-NI
[2] https://github.com/usnistgov/jsfive

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