AW: [Proj] Re: wrong computation of meridinal distance / pj mlfn.
c
Albert Peter
Peter.Albert at dwd.de
Wed Jul 13 11:52:26 EDT 2005
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
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