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Gerald I. Evenden | 2 Jun 2009 19:57
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NTv2 info

Kudos to the Swiss---so far they are the only ones that seem to have format 
information on the NTv2 correction files.

A slap on the face with cold, wet noodles to the Canadians because I cannot 
locate any format details on the Canadian NTv2 distribution file.  The only 
thing I can find is the documenation of a program to access the file, which 
deserves another slap for not being available in source form.

I seem to get the idea that the Canadians developed this format---comments 
please---and if they did then the designers deserve to be flogged for 8 days 
with wet noodles for "positive east longitude."  I can't believe it!!!!  What 
is unbelievable arrogance by whoever had that stupid---yes, *VERY* 
stupid---idea.  I was looking at the headers of a Swiss NTv2 file and sure 
enough, negative values for longitude.  What's in that Molson anyway?  The 
McKenzie brothers must have been co-chairing the development commitee.

An intersting aside demonstrated by the Swiss distribution: the compress ASCII 
version of the NTv2 file is slightly smaller than the binary version.  
Wouldn't it have been nice if the McKenzie brothers looked into this when 
spec'ing the output form and saved everyone from the curse of determining 
endian conversion?

There is a problem with the Swiss documentation: it is in German and the 
details of the data records is not as clear as the headers.

Obviously, I have not exhausted all possible 4,000 google hits in looking for 
documentation.  If someone is aware of a defining english pdf somewhere, 
please let me know.  Thanks.

--

--
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Brent Fraser | 2 Jun 2009 20:36

Re: NTv2 info

My government at work, *sigh*.  What they don't tell you is there is more information (including Fortran
source code) on $20 CD than available for download on their website (http://www.geod.nrcan.gc.ca/tools-outils/ntv2_e.php)

Best Regards,
Brent Fraser
GeoAnalytic Inc.

Gerald I. Evenden wrote:
> Kudos to the Swiss---so far they are the only ones that seem to have format 
> information on the NTv2 correction files.
> 
> A slap on the face with cold, wet noodles to the Canadians because I cannot 
> locate any format details on the Canadian NTv2 distribution file.  The only 
> thing I can find is the documenation of a program to access the file, which 
> deserves another slap for not being available in source form.
> 
> I seem to get the idea that the Canadians developed this format---comments 
> please---and if they did then the designers deserve to be flogged for 8 days 
> with wet noodles for "positive east longitude."  I can't believe it!!!!  What 
> is unbelievable arrogance by whoever had that stupid---yes, *VERY* 
> stupid---idea.  I was looking at the headers of a Swiss NTv2 file and sure 
> enough, negative values for longitude.  What's in that Molson anyway?  The 
> McKenzie brothers must have been co-chairing the development commitee.
> 
> An intersting aside demonstrated by the Swiss distribution: the compress ASCII 
> version of the NTv2 file is slightly smaller than the binary version.  
> Wouldn't it have been nice if the McKenzie brothers looked into this when 
> spec'ing the output form and saved everyone from the curse of determining 
> endian conversion?
>
(Continue reading)

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Cuinet Jérôme | 2 Jun 2009 21:14
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Re: NTv2 info

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

----- Original Message ----- 
From: "Gerald I. Evenden" <geraldi.evenden <at> gmail.com>
To: "PROJ.4 and general Projections Discussions" <proj <at> lists.maptools.org>
Sent: Tuesday, June 02, 2009 7:57 PM
Subject: [Proj] NTv2 info

> Kudos to the Swiss---so far they are the only ones that seem to have 
> format
> information on the NTv2 correction files.
>
> A slap on the face with cold, wet noodles to the Canadians because I 
> cannot
> locate any format details on the Canadian NTv2 distribution file.  The 
> only
> thing I can find is the documenation of a program to access the file, 
> which
> deserves another slap for not being available in source form.
>
> I seem to get the idea that the Canadians developed this format---comments
(Continue reading)

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Gerald I. Evenden | 2 Jun 2009 21:41
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Re: NTv2 info

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.  ;-)
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Frank Warmerdam | 2 Jun 2009 21:50
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Re: NTv2 info


Folks,

I would add that there is NTv2 reading and utilization code in the PROJ.4
code.  Search on "ntv2" in files like pj_gridinfo.c.

Byte swapping and axis orientation are really not a big issue as long as
they are unambiguous.

Best regards,
--

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam <at> pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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Gerald I. Evenden | 2 Jun 2009 23:07
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Re: NTv2 info

On Tuesday 02 June 2009 3:50:33 pm Frank Warmerdam wrote:
> Folks,
>
> I would add that there is NTv2 reading and utilization code in the PROJ.4
> code.  Search on "ntv2" in files like pj_gridinfo.c.
>
> Byte swapping and axis orientation are really not a big issue as long as
> they are unambiguous.
>
> Best regards,

How do you think I got involved with NTv2?

I never heard of NTv2 before because I have not been involved with datum 
stuff.

The bizarre material in pj_gridinfo.c meant that I had to research it out and 
try to get the whole story.  Or, at least, a bit more.

On a previous email I meant *binary* data transfer between different CPU's is 
a problem.

Some other material surfaced that shows that the NTv2 material much more 
whacky than just the positive west longitude.  It has to be the product of 
the McKenzie brother's R&D company.

--

-- 
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
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Clifford J Mugnier | 2 Jun 2009 23:08
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Re: NTv2 info

This phenomenon might be termed "hemispherical ethnocentric geodetics" complicated by ellipsoids ...
 
Once had to write a translator to get the extended character set to compile properly between Intel compilers and Unix compilers.
 
C. Mugnier
LOUISIANA STATE UNIVERSITY

From: proj-bounces <at> lists.maptools.org on behalf of Gerald I. Evenden
Sent: Tue 02-Jun-09 14:41
To: Cuinet Jérôme
Cc: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] NTv2 info

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
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Gerald I. Evenden | 3 Jun 2009 04:03
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Re: NTv2 info

We have our answer to the McKenzie brothers in the US and they go by the names 
of Larry, Mo and Curly.  Another one occasionally shows up called Shemp.

They were last seen in Redmond, Washington and rumorred to be in charge of a 
large software company's R&D unit.

As an aside: the first micros (68000 Motorola micros) that we installed in the 
computer room in Woods Hole circa the 80s were called Larry, Mo and Curley.  
They were all Unix systems and connected with an ethernet cable as thick as 
my thumb.

--

-- 
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
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stephane.poirier | 3 Jun 2009 07:38
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How to derive projections definitions from North American LCC and Polar Stereographic rendered maps rasters?

Hi All,
 
1) Is there a way to derive projection parameters strictly from the rendered raster information of 
 
2) Would this, here below, be a close enough proj4js definition for the polar stereographic here above?
Proj4js.defs["EPSG:CRCM"] = "+proj=stere +lat_0=90 +lat_ts=60 +lon_0=-97 +k=1 +x_0=3450000 +y_0=7450000 +ellps=WGS84 +datum=WGS84 +units=m" (CRCM being our own custom EPSG string tag).
 
Regards,
 
 
Stephane Poirier, M.Sc. Optics Physics
Remote Sensing Research Professional
University of Sherbrooke, QC, Canada
Stephane.Poirier <at> USherbrooke.ca
http://www.usherbrooke.ca/cartel 
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Paul Kelly | 3 Jun 2009 11:06
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Re: NTv2 info

See the below link for an account of my own naive experimentations with 
the NTv2 format a few years ago - perhaps not of great interest though as 
I too could not find any adequate documentation for the binary version of 
the file and indeed used some Windows software (Australian) to create a 
binary version from the ASCII.

Link: <http://www.stjohnspoint.co.uk/gis/france.htm>
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Gmane