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

[Gerald I. Evenden]

On Thursday 15 June 2006 3:10 am, Melita Kennedy wrote:
> > Cliff Mugnier wrote:
> > Melita Kennedy of ESRI informed me a couple years ago that they
> > successfully programmed Jeff Dozier's TM equations and have incorporated
> > that routine into one of the ESRI packages, I don't remember which one.
>
> David Burrows implemented a complex math version of transverse Mercator
> working from Dozier's equations. On a brief stop in the office today (he's
> on vacation), he couldn't remember any errors in Dozier's equations
> off-hand. He did mention that he could not make it work out to 90 degrees
> from the central meridian as the paper states. I think we ended up limiting
> it to 85 or 87 degrees. Next week he'll take a look at  his copy of the
> paper to see if he wrote any notes down.
>
> Melita

I managed to dig out my old work with the Dozier package---dates on the files 
are 2003.

I AGAIN compared my original copy of his original paper code and noted a few  
problems I detected several years ago:

1. I had to add a header file to all files to define the complex declaration:
typedef struct {
        double re, im;
} complex;

2. Three files did not declare complex functions---which were added.

3. Around line 70 in file tmw.c I did the following change:
/* old
     70     ms.re *= m;
     71     ms.im *= m;
     72   new */
     73     ms.re *= k_tran;
     74     ms.im *= k_tran;
     75 /* end change */
At the moment I would have to dig for my reason.

I did get the code to run but could not get it to agree with tmerc to better 
than about .1%.  Obviously, not very good.  (also in the lon < 3degree 
range).

There are a number of questionable code practices but most are unlikely to 
produce errors.  The code is VERY early K&R and would be GREATLY improved 
with updating to modern declarative standards.  Most, if not all, of the 
basic complex routines are available in either C99 library or GSL (Gnu 
Scientific Library).

After I hopefully solve my problems with the French version I will try to 
regress to my 2003 problems with Dozier.  If anyone has any news of Dozier's 
reexamining this material I would be greatly appreciative of learning of any 
errata.
-- 
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary