[PROJ] NTv2 grid file from Bessel ellipsoid to Bessel ellipsoid

[Even Rouault]

> > For what you describe in your needs, you'd better use PROJ 5.2 or the
> > nearly released PROJ 6.0 and use PROJ pipelines
> 
> I know, but I would like to be able to do the same with Proj.4, to share it
> with the many users that still use this version.

By the way, you can use PROJ 6 with the "proj-dev" package of OSGeo4W.

> 
> > given what the code does (which of course is true of any bug :-)).
> 
> 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'm not sure if PROJ and GDAL implementations have been done from reverse 
engineering of examples or from a format description.

> Anyway, thanks for the explanation. Now I am able to get what I need like
> this with Proj.4:

Clearly good candidates to use multistep pipeline :-)

Even

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