[Proj] Terminology for origins

[Clifford J Mugnier]

Sorry you find it contradictory, but it remains a fact.  When you get to zero and still need to go further south to use the same grid system, they add an additional number to that zero for a significant "jump."  I have not ever seen it used for False Easting; just for False Northing.  
 
The French Lambert Sud Algerie Grid has a False Northing of 300 km at the origin of 33º 18' North.  ("South of the False Origin add 1,000,000 meters to the northings").  The original grid tables are Tables de Projeciton Systeme Lambert Nort Maroc.  The EPSG has an interesting database for such things, however I consider my personal holdings as authoritative in most cases that differ.  This is one of those common cases.  
 
Regards,
 
Clifford J. Mugnier, C.P., C.M.S.
Past National Director (2006-2008),
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American Society for Photogrammetry and Remote Sensing 
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________________________________

From: proj-bounces at lists.maptools.org on behalf of Mikael Rittri
Sent: Mon 06-Oct-08 02:03
To: PROJ.4 and general Projections Discussions
Subject: RE: [Proj] Terminology for origins


Clifford J Mugnier wrote ( http://lists.maptools.org/pipermail/proj/2008-October/003865.html ):
 
> In North Africa, several of the Grids also have a False Northing at the False Origin in order to avoid negative northings.
> Really!
> :-) 
 
Sorry, I don't understand.  In what sense are you using the term "False Origin" here?  
 
If you are using it as EPSG does (at least for Lambert Conformal Conic 2SP 
and Polar Stereographic Variant C), then your statement is not surprising, since 
that's how such a False Origin works: it does have a False Northing and a 
False Easting. 
 
If you are using it in the other sense, as the point where False Easting and False Northing
are both zero, then your statement is contradictory (that's a little too surprising). 
 
So, you must be using the term "False Origin" in some third, more general way.  
Could you give a concrete numerical example? 
 
Best regards,
 
--
Mikael Rittri
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