[Proj] Problems with Pittman geodesic??
Gerald I. Evenden
geraldi.evenden at gmail.com
Thu Jan 22 15:40:40 EST 2009
On Monday 19 January 2009 1:16:38 pm OvV_HN wrote:
> Some time ago I referred to 2 articles by Saito.
> He computes the geodesic problems by numerical integration. There are some
> errors in the formulae, but his second article gives correct results for
> 'normal' values. Saito attends much detail to borderline situations, but
> there are probably some errors in his descriptions.
> Anyhow, he gives a couple of test points which everybody with geodesics
> code definitively should try to replicate. You might be surprised!
I did not find any surprises here because where problems do show up are for
the near apodal points which Vincenty (and others) usually flunk.
I have more problems with failures with Pittman and some non-apodal points.
> Saito article 2 examples.
>
> Using the formulas and the procedure described in the article, with an
> equatorial radius of 6378388 meters and an inverse flattening of 297, the
> following results were obtained. The computation was made in double
> precision arithmetic - through twenty significant digits.
"double precision" --- "through twenty significant digits." ??? What kind of
hardware is being used? "double" on most 64bit systems is about 15 digits
+-. With so much significance, why are the following tables showing 12 at
best?
> Line lat1 lat2 delta lon
> 1. 37d 19' 54.95367" 26d 07' 42.83946" 041d 28' 35.50729"
> 2. 35 16 11.24862 67 22 14.77638 137 47 28.31435
> 3. 01 00 00.00000 -00 59 53.83076 179 17 48.02997
> 4. 01 00 00.00000 01 01 15.18952 179 46 17.84244
> 5. 41 41 45.88000 41 41 46.20000 000 00 00.56000
> 6. 30 00 00.00000 37 53 32.46584 116 19 16.68843
> 7. 30 19 54.95367 -30 11 50.15681 179 58 17.84244
> 8. 00 39 49.12586 -00 45 14.13112 179 58 17.84244
> 9. 00 00 54.95367 00 00 42.83946 179 28 17.84244
>
> Line dist. azim. back azim.
> 1. 4085966.7026 m 095d 27' 59.630899" 118d 05' 58.961609"
> 2. 8084823.8383 015 44 23.748498 114 55 39.921473
> 3. 19959999.9998 088 59 59.998971 091 00 06.118356
> 4. 19780006.5588 004 59 59.999957 174 59 59.884800
> 5. 16.2839751 052 40 39.390671 052 40 39.763172
> 6. 10002499.9999 045 00 00.000004 129 08 12.326009
> 7. 19989590.5480 002 23 52.108130 177 36 19.670109
> 8. 19994529.4446 177 39 39.010104 002 20 21.153036
> 9. 19977290.7711 054 08 27.731619 125 51 32.272327
>
> From:
> THE COMPUTATION OF LONG GEODESICS ON THE ELLIPSOID
> THROUGH GAUSSlAN QUADRATURE
> Tsutomu SAITO
Using Gaussian Quadrature is not a big thing as long as one has the integrals
to evaluate---one does not need to use gsl to do that. ;-) I am surprised
that he can get away with just using that method---or does he?
Lastly, the Saito source is apparently available though "Springer --
something" that charges $35(presumably US) for a pdf copy of Vincenty that
you can get for free from NOAA.
--
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist
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