[Proj] Libproj4 manual opinion poll

Gerald I. Evenden geraldi.evenden at gmail.com
Mon Sep 29 16:05:32 EDT 2008

On Monday 29 September 2008 1:34:56 pm Clifford J Mugnier wrote:
> Normal Mercator can indeed have "2 standard parallels," but they are always
> symmetric about the Equator.  I have done one that is legally recognized in
> Ecuador for the city of Guayaquil to cover a larger area of interest
> outside of the old city limits (for the greater Metro area), with minimal
> scale distortion.  It is simply done by having a scale factor at origin
> less than 1.0 at the Equator.
> Watch your blood pressure.
> C. Mugnier
> Louisiana State University

Obviously one has symmetrical reflection of the latitude of true scale across 
the equator and "two standard parallels" but the context that was used in one 
of the sources of information about projections was that the second standard 
parallel was denoted as being the latitude of the projection origin---lat_0.  
This would actually generate 4 standard parallels considering sysmmetry. I do 
not remember whether Ecuador uses lat_ts or k_0---two means to the same end.  
Hmmm.  Looks like Ecuador normally uses k_0 which make sense for a grid 
system at the equator.

For navigation maps I have seen, lat_ts used most frequently.

What I objected to was the shifting of origin by the so-called second parallel 
and believe that in the case of Mercator shifting of origin is most easily 
taken care of by y_0 or false-northing.  I think is was the EPSG that had the 
funky spec entry but at the moment I can't find it.  This is where my blood 
boils.  ;-)

I once acquiesced to doing such nonsense of adding a lat_0 for another 
cylindrical but have kicked myself ever  since.
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist

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