[Proj] NTv2 info

[Gerald I. Evenden]

On Tuesday 02 June 2009 3:14:37 pm Cuinet Jérôme wrote:
> We can see the existence of a NTV2 Developer's Guide Junkins and Farley,
> 1995, but any link is broken. The closest document is a NTV2 User's Guide
> that you have pointed.
>
> This developper guide must be on some computers...
>
>
> How silly we are, using a canadian built-in format. Fortunately it wasn't
> an Autralian format ! By talking australians, they noticed that NTv2 format
> had seemed to be compiler dependant, although it is finally not compiler
> dependant : http://www.geom.unimelb.edu.au/gda94/NTv2_Binary.pdf
>

It is what seems to be most commonly call "endian" dependent.  That is; if a 
character string of 8 bytes is overlayed on a type double word, is the first 
byte of the string at the begining of the float word or at the end.  That is, 
the byte string might be in reverse order.

In the case of reading the NTv2 format one must reverse order the bytes of the 
float and double words in the file before they make sense to an Intel or 
clone CPU (read "Microsoft").

In the case of the NGS NADCON files, an Intel machine can process them without 
byte flipping.

Data transfer among different CPUs can be a *REAL* headache!

If it was an Australian format, latitude would be positive south of the 
equator.  ;-)

-- 
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist