[PROJ] NTV2 format

[Even Rouault]

On lundi 25 février 2019 21:16:47 CET Martin Desruisseaux wrote:
> Le 25/02/2019 à 21:12, Even Rouault a écrit :
> >> I thought it was a bug, since I also noticed that de code ignores the
> >> setting for GS_TYPE in the header of de NTv2 (.gsb) file: if this is
> >> not set to seconds, it still assumes seconds.
> > 
> > Yes, this field of the header is ignored. But out of curiousity, are
> > there other possible values ? Do you have a link to a specification of
> > the format ?
> 
> I do not remember where I got the specification, but on my side I have
> the following possible values for GS_TYPE: "SECONDS", "MINUTES" or "DEGREES"

Thanks. Actually I just found
https://github.com/Esri/ntv2-file-routines which documents this. The original 
documentation from the Canadian government seems to have disappeared.

Is anyone aware of .gsb files in the wild using GS_TYPE != SECONDS ?
The above link mentions "All published NTv2 files that we have seen have a 
GS_TYPE of "SECONDS". This has the advantage that the latitude, longitude,
and increment values in the sub-file records are then usually whole numbers."

Even

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