[OSRS-PROJ] Donald Elliptic Projection for AT&T V&H Coordinates?

Clifford J Mugnier cjmce at lsu.edu
Mon Dec 2 11:41:52 EST 2002

It was the U.S. Coast & Geodetic Survey that had the WWI faux pas; AMS was
not in existence then.

In regard to accuracy, the published specification for NAD83
transformations is "better than 0.1 mm."  (re: Jim Stem, NGS) For the
NAD27, generally 0.01 ft is more than adequate; the original tables would
only yield about 0.05 ft computational accuracy.  (That's because they used
a "short-cut" for latitude - geocentric). (re: John Snyder)

Most foreign stuff published BEFORE WWII was considered adequate to 0.1
meters (computational) accuracy by the British.  The French were not much

I agree that it's particularly knotty to scrounge "test points," and it is
of critical importance nowadays with two different direction conventions
for rotation angles being used in 7-parameter datum shift transformations.
The Americans & Australians do it one way, the Europeans do it the other
way, naturally.

Cliff Mugnier
I couldn't agree more with your message and it was inexcusably sloppy of
USAMS to not verify their projection with the existing charts/numbers of

One of the biggest problems I've had in coding projections is to find
to compare the execution of my code.  Once you leave the area of the 20 odd
projections supplied by the USGS GCTP, making comparisons is very, very

Secondly, how close should the comparison be?  For conformal projections
and any involved in plane coordinate system usage, projections should agree
to 1 mm.  Some of my codings are more accurate than alternate
source code simply because I have found it trivial to extend the precision
of some series to the ~15 digit limits of type double.

Clifford J Mugnier wrote:

> Mr. Evenden,
> I was not upset, just pointing out historical facts on projection math.
> The French could not "correct their maps.  :-)" because the maps were
> already printed and the "Bosch" were occupying their country.  The work
> that the C&GS tried to interceed with was with the estranged French
> Topographic Corps residing in London.
> The French only "corrected" their math in 1948 after WWII.  It took the
> U.S. Army Map Service to (mathematically and figuratively) "bop" them in
> between the eyes with a ball peen hammer before they changed to a fully
> conformal Lambert conic.  By that time, the rest of Europe was on the
> European Datum, UTM Grid.  Some prior French colonies (in North Africa)
> still cling to that old artifact of the French Army Truncated Cubic
> Conic.
> Screwy or not, it's what's implemented is what counts for the locals.
> Cliff Mugnier


PROJ.4 Discussion List
See http://www.remotesensing.org/proj for subscription, unsubscription
and other information.

PROJ.4 Discussion List
See http://www.remotesensing.org/proj for subscription, unsubscription
and other information.

More information about the Proj mailing list