[Proj] Grown error if re-projecting from 4269 to LCC (2285) and backward multiple times

Clifford J Mugnier cjmce at lsu.edu
Fri Nov 3 09:54:17 EST 2017

The French Army Truncated Cubic Lambert (partially conformal) Conic projection is the Legal system for the projection in France between the late 1800s and 1948 when the French Legislature changed the law to recognize the fully conformal version.  It was (might still be in one or two North African prior French Colonies) used in North Africa in Algeria, Tunisia, & Morocco, as well as in Syria during the Levant.

Last time I have seen it used was about 30+ years ago in Algeria when it was used to define Lease Block boundaries for Petroleum Exploration & Production.

Clifford J. Mugnier, c.p., c.m.s.

Chief of Geodesy

LSU Center for GeoInformatics (ERAD 266)

Dept. of Civil Engineering (P.F. Taylor 3531)


Baton Rouge, LA  70803

Academic: (225) 578-8536

Research: (225) 578-4578

Cell:             (225) 328-8975

honorary lifetime member, lsps

fellow emeritus, asprs

member, apsg

From: proj-bounces at lists.maptools.org <proj-bounces at lists.maptools.org> on behalf of vanadovv at hetnet.nl <vanadovv at hetnet.nl>
Sent: Friday, November 3, 2017 6:25 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Grown error if re-projecting from 4269 to LCC (2285) and backward multiple times

I completely forgot about the LCCA projection, discussed some years ago.
But, LCCA is not LCCA.
The discussion around the PJ_lcca.c code seems to refer to the Lambert Conic Near-Conformal projection, fully documented in the EPSG Guidance Note 7-2.
This projection is also fully documented in the Libproj4 manual from Gerald Evenden, as the Lambert Conformal Conic Alternative Projection.
The code from Libproj is used in PROJ. The libproj/proj algorithms are completely different from the EPSG algorithms.
Eitherway: indeed, do not use this code for regular LCC projections!

 Oscar van Vlijmen

----Origineel Bericht----
Van : knudsen.thomas at gmail.com
Datum : 02/11/2017 22:55
Aan : proj at lists.maptools.org
Onderwerp : Re: [Proj] Grown error if re-projecting from 4269 to LCC (2285) and backward multiple times

Hi Dmitry,

I googled around for the “alternative” Lambert, without luck, but then this afternoon, I accidentally misspelled Lambert as “Lamber”, and ran into this thread: http://lists.maptools.org/pipermail/proj/2003-March/000644.html where PROJ.4 founder Gerald Evenden, and long time PROJ.4 maintainer Frank Warmerdam discusses the LCCA, and Gerald mentions that it is a truncated series, only introduced to be compatible with some legacy French/North African systems, that were defined using the truncated series.

Gerald explicitly states that it should not be used for new work, so my recommendation of looking at it was terribly bad advice. Also, I had not realized that LCCA does not support the secant (“2 parallel”) case, and hence lat_0 and not lat_1 & lat_2 are used for parameterizing the projection.

So enough about LCCA - it should not be used for anything but to maintain interoperability with legacy reference systems.


[more: see original message]

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