[Proj] Re: Discovery: libproj4 stmerc = French Gauss-Laborde projection

Gerald I. Evenden gerald.evenden at verizon.net
Mon Jun 26 16:16:04 EDT 2006

On Wednesday 14 June 2006 1:12 am, Strebe at aol.com wrote:
> You might contact Dr. David E. Wallis. He devised a much simpler method
> than Dozier's. I've implemented it for the full-ellipsoid. You can see a
> plot of an earth-like ellipsoid here:
> http://mapthematics.com/Projection%20Images/Cylindrical/Transverse%20Mercat
>or. GIF
> The method works for arbitrary eccentricities. Contact me privately if
> you're interested. Since it is Dr. Wallis's invention, I'll put you in
> contact with him.

I wrote to the address on the web site but letter was returned undeliverable.  
I suspect that the web page is several years old and not maintained.

Not to beat a dead horse of several years ago, I have stared at the above gif 
and it still bothers me and it does not seem real.  The cusps at the ends of 
the equator seem unnatural.  Also, why does both of the other procedures that 
we have looked at all contain discontinuities at the limits---most commonly, 
they require isometric latitude which fails at 90 degrees.  What magic twist 
allows Wallis to come up with the above map when all others want to extend to 
infinity?  Is it truly a normal transverse mercator where the scale factor is 
1. along the central meridian?  Has that been checked?  Sorry, I am still a 
skeptic until I see the math and a functional program that can demonstrate 
the conformal properties of the projection.

The cusps at the ends of the equator sure look like violations of conformality 
to me.

As previously noted, the French TM has been added to libproj4 and the Dozier 
procedure has also been pretty well conquered and will be add to 
libproj4---probably as dtmerc.  Neither of these routines will do |lat|=90 
nor |lon|=90.
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary

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