Re: [Proj] wrong computation of meridinal distance / pj mlfn.c
Peter Albert
peter.albert at gmx.de
Wed Jul 13 02:09:58 EDT 2005
Hi Noel,
> Don't have a solution for you, but I have duplicated your
> MuPAD computations
> with similar numerical integrations in Matlab. So, that's cool.
I also duplicated the computations in IDL, but this is very similar to
Matlab, so that's no wonder.
> also dusted off a meridional arc function from an old
> TM code and duplicated
> Proj.4's computation as well. So, that's cool, too.
I don't know what TM is, but if I understand you correctly you did the
elliptical integral here, not the polynomial approximation as in Proj? In
that case a look at the code would probably be helpful. Could you provide me
with this?
> Rather, my intuition suggests that either MuPAD and Matlab are
> integrating over a prolate (egg-shaped) ellipsoid (not oblate)
Hm, I am lost here; my english-german dictionary gives the same translation
for both "oblate" and "prolate"... is there a way you could illustrate the
difference between both?
> or that the
> zero latitude is interpreted differently (vertically?).
> Don't know why that
> would be so, but worth investigating. Too late tonight, however.
Well, in the MuPAD calculations I for sure interpreted latitude as being 0°
at the equator and 90° at the pole, the elliptical integral I used for the
calculations is based on the definition of the ellipse x=a*cos(t) and
y=b*sin(t), so zero latitude is on the equator with x=a and y=0.
Regards,
Peter
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