# [Proj] Info on proj4 formulas

Clifford J Mugnier cjmce at lsu.edu
Fri May 9 12:59:47 EST 2014

```Variations in projection formulae can be an academic exercise or a catastrophe, depending on the application.  Most GIS applications can use practically any truncation of the infinite series (4th order, 5th order, 6th order, etc.) with little to no effect to day-to-day work.  There are two exceptions:

1.)	Military.  Always use whatever is currently promulgated by NGA for NATO/SEATO applications.  This helps avoid “friendly fire” incidents among units that provide indirect fire support.

2.)	Oil and Gas.  Exploration and Production concessions leased by national governments use map projections for Grid Systems as legal coordinate systems sometimes based on specific truncations.  When that is in effect, the use of other truncations (especially in offshore areas) can produce catastrophic errors in positioning.

Sometimes, mathematical distortions at various distances from the projection origin are on purpose!

Cliff Mugnier
LOUISIANA STATE UNIVERSITY
________________________________________
From: proj-bounces at lists.maptools.org <proj-bounces at lists.maptools.org> on behalf of Hermann Peifer <peifer at gmx.eu>
Sent: Friday, May 9, 2014 12:47 PM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Info on proj4 formulas

On 2014-05-09 16:31, Nick Ves wrote:
> Intresting,
>
> But now I'm wondering if the OGP's "Geomatics Guidance Note Number 7,
> part 2 Coordinate Conversions and Transformations including Formulas"
> [0] has been taken into account in the realizations of the formulas.
>
> [0] http://www.ogp.org.uk/pubs/373-07-2.pdf
>

At least Thomas Flemming mentions an earlier version of the guidance
note, see http://trac.osgeo.org/proj/browser/trunk/proj/src/PJ_krovak.c

Hermann

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