[Proj] Lambert Conformal Conic
Clifford J Mugnier
cjmce at lsu.edu
Mon Apr 27 10:24:32 EST 2009
The GeoTrans maintainers are keeping Warfighters alive. Period. If hundreds of weapons systems are currently programmed for a particular constant, say "81.114528," what is the effect (of a change in GeoTrans) going to be on each and every one of those weapon systems? Based on what some obscure programmer did 15-20 years ago for one system's coordinate transformation utility ... who can guarantee that there will be absolutely no possible chance of an untested error creeping in now and resulting in "friendly fire?"
Frozen-in approximate constants remain frozen-in for a reason, especially when using coordinates for indirect artillery fire and air support.
On a less serious (not involving life and death), application, specific truncations kept over from 19th-century mathematical developments may not be computationally elegant or "correct" in the strictest sense, but they are the absolutely necessary truncations that must be maintained for a particular country's legal system. Offshore Leases for hydrocarbon exploration and production are worth billions of dollars each, and truncations define areas that would change if the transformations were arbitrarily changed for the sake of elegance.
P.S. A rumor has circulated in the Military Geodetic circles for decades that 0.994 in the UPS is actually an old "typo," and should really be 0.9994. However, it can never be changed because it has been hard-wired into everything (weapon systems) as well as into thousands of editions of paper maps. Mathematical elegance comes second to Warfighter's lives.
From: proj-bounces at lists.maptools.org on behalf of Karney, Charles
Sent: Sun 26-Apr-09 19:01
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Lambert Conformal Conic
Another example of frozen-in approximate constants...
geotrans (thru at least version 2.4.2) defines the latitude of true
scale for the UPS projection as 81.114528 (see definition of
MAX_ORIGIN_LAT in ups/ups.c). However, if we assume that UPS is defined
as having a scale of 0.994 at the pole, then the latitude of true scale
is really 81.11451786859362545 or so.
I reported this to the geotrans maintainers in July of last year and
they declined to fix it because doing so would cause their (presumably
incorrect) tests to fail!
Charles Karney <ckarney at sarnoff.com>
Sarnoff Corporation, Princeton, NJ 08543-5300
Tel: +1 609 734 2312
Fax: +1 609 734 2662
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