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

Gerald I. Evenden gerald.evenden at verizon.net
Wed Jun 14 21:38:06 EDT 2006

On Tuesday 13 June 2006 2:59 pm, Oscar van Vlijmen wrote:
> I checked my results with an on-line calculator from professor Schuhr,
> based on the Klotz algorithms.
> <http://gauss.fb1.fh-frankfurt.de/cgi-bin/cgi_gk>
> This calculator fails for difficult areas (very large lon-lon0, small lat).
> So I can only 'proof' my results in the difficult areas by doing a complete
> round-trip and getting nearly the original data back.

I finally cased out usage of the above site and agree that within the limits
of 6 degrees from the central meridian lproj agrees to about .1mm.  However, I 
did note that the above site's northing fails near the pole.  This is 
dependent upon the accuracy of the meridianal distance algorithm and where 
lproj's should be good to about 14 digits or about .1 nm.

Given the labor of hand keying test values on an online site, the test was not 
very rigorous.

I might have been able to push meridianal distance to IEEE 64 bit float limits 
but my interest in the project was began to wane.

With the exception of northing, lproj seems to agree to the .1mm of the site's 
display precision within the 3.5 degree range of UTM.  This range is certain 
the practical limits of TM.
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary

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