<HTML dir=ltr><HEAD><TITLE>Re: [Proj] NTv2 info</TITLE>
<META http-equiv=Content-Type content="text/html; charset=unicode">
<META content="MSHTML 6.00.6000.16825" name=GENERATOR></HEAD>
<BODY>
<DIV id=idOWAReplyText19877 dir=ltr>
<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=2>This phenomenon might be termed "hemispherical ethnocentric geodetics" complicated by ellipsoids ...</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>Once had to write a translator to get the extended character set to compile properly between Intel compilers and Unix compilers.</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>C. Mugnier</FONT></DIV>
<DIV dir=ltr><FONT size=2>LOUISIANA STATE UNIVERSITY</FONT></DIV></DIV>
<DIV dir=ltr><BR>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> proj-bounces@lists.maptools.org on behalf of Gerald I. Evenden<BR><B>Sent:</B> Tue 02-Jun-09 14:41<BR><B>To:</B> Cuinet Jérôme<BR><B>Cc:</B> PROJ.4 and general Projections Discussions<BR><B>Subject:</B> Re: [Proj] NTv2 info<BR></FONT><BR></DIV>
<DIV>
<P><FONT size=2>On Tuesday 02 June 2009 3:14:37 pm Cuinet Jérôme wrote:<BR>> We can see the existence of a NTV2 Developer's Guide Junkins and Farley,<BR>> 1995, but any link is broken. The closest document is a NTV2 User's Guide<BR>> that you have pointed.<BR>><BR>> This developper guide must be on some computers...<BR>><BR>><BR>> How silly we are, using a canadian built-in format. Fortunately it wasn't<BR>> an Autralian format ! By talking australians, they noticed that NTv2 format<BR>> had seemed to be compiler dependant, although it is finally not compiler<BR>> dependant : <A href="http://www.geom.unimelb.edu.au/gda94/NTv2_Binary.pdf">http://www.geom.unimelb.edu.au/gda94/NTv2_Binary.pdf</A><BR>><BR><BR>It is what seems to be most commonly call "endian" dependent. That is; if a<BR>character string of 8 bytes is overlayed on a type double word, is the first<BR>byte of the string at the begining of the float word or at the end. That is,<BR>the byte string might be in reverse order.<BR><BR>In the case of reading the NTv2 format one must reverse order the bytes of the<BR>float and double words in the file before they make sense to an Intel or<BR>clone CPU (read "Microsoft").<BR><BR>In the case of the NGS NADCON files, an Intel machine can process them without<BR>byte flipping.<BR><BR>Data transfer among different CPUs can be a *REAL* headache!<BR><BR>If it was an Australian format, latitude would be positive south of the<BR>equator. ;-)<BR><BR>--<BR>The whole religious complexion of the modern world is due<BR>to the absence from Jerusalem of a lunatic asylum.<BR>-- Havelock Ellis (1859-1939) British psychologist<BR>_______________________________________________<BR>Proj mailing list<BR>Proj@lists.maptools.org<BR><A href="http://lists.maptools.org/mailman/listinfo/proj">http://lists.maptools.org/mailman/listinfo/proj</A><BR></FONT></P></DIV></BODY></HTML>