[Proj] Implementation(s) and ensuing headaches ...

Clifford J Mugnier cjmce at lsu.edu
Tue Oct 25 16:45:38 EDT 2005

The generally accepted "standard" for computational accuracy (late 20th
century - 1990s) is to match a government's projection tables or government
transformation software to 0.1 mm in both components.

The equivalent "standard" for computational accuracy (late 19th century)
was to match a government's projection tables to 0.1 meters in both
components.  (Plenty good enuf' for controlling indirect artillery fire.)

When old formulae, based on double projections (Equivalent Spheres and
Latitude Functions - Authalic, Conformal, Rectifying, etc.), are used
nowadays ... it can get quite challenging to find an analytic expression to
match today's standards.

The classic work by Charles N. Claire, "Special Publication 65-1, State
Plane Coordinates by Automatic Data Processing Methods" was just such an
example of the extra hoops the U.S. Coast & Geodetic Survey had to jump
through in an attempt to match the ole-timey tables of the State Plane
Coordinate Systems of the United States.  John P. Snyder once wryly noted
that one of the dilemmas faced by Claire was that Oscar S. Adams had chosen
to use Geocentric Latitude rather than Conformal Latitude in his Lambert
Tables (to save time back then since it was 'good enuf' back then).  Only
Claire didn't know that at the time, just that he had to match the old
tables ... !

And so, history continues to repeat itself.


Clifford J. Mugnier
Chief of Geodesy and
Associate Director,
Department of Civil Engineering
CEBA 3223A
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic]
Voice and Facsimile:  (225) 578-4474 [Research]

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