AW: [Proj] Re: wrong computation of meridinal distance / pj mlfn. c

[Albert Peter]

Gerald,

thanks for your answer.

> For the math involved see the section in the libproj4 manual (p. 24) 
> on the web site
> http://members.verizon.net/~vze2hc4d/proj4
<http://members.verizon.net/~vze2hc4d/proj4> 

that helped a bit further: when I plug your formula into MuPAD I can at
least reproduce proj's results, which is good. So it is not the mysterious
polynomial approximation anymore. I will go and try to understand where
"your" formula comes from. 

> Note that all references to latitude in the manual are to the geodetic 
> latitude.
> Geocentric is only of interest to satellite problems and I can't 
> imagine that substituting the geocentric form into the integral would 
> simplify the solution.

Well, I actually did not substitute it but rather started from the
definition of the ellipse as

x=a*cos(t) and y=b*sin(t),

where for t the geocentric latitude has to be taken.

Then the arc length ds id

ds = sqrt( (dx/dt)^2 + (dy/dt)^2 ) dt

which brought me to the formuala I used.

So, currently I don't see where the mistake in this approach lies.

Best regards,

   Peter