| Subject: | Math::Trig::great_circle_destination |
| Date: | Thu, 20 Mar 2008 01:56:05 +0200 |
| To: | bug-Math-Complex [...] rt.cpan.org |
| From: | "Otto J. Makela" <om [...] iki.fi> |
It seems Math::Trig::great_circle_destination has some weirdness?
The following code is based on the manual page example, which work fine,
but my call to great_circle_destination ends up with a strange phi value.
To be exact, phi seems to be 90° wrong, maybe the inverse of substracting this
value done in the NESW function isn't done before returning, as just doing a
rad2deg of the value returned seems to give the right number?
---- code ----
#!/usr/bin/perl -w
use strict;
use Math::Trig qw(deg2rad rad2deg :pi :great_circle);
# Notice the 90 - latitude: phi zero is at the North Pole.
sub NESW { deg2rad($_[0]), deg2rad(90 - $_[1]) }
my @L = NESW( -0.5, 51.3);
my @T = NESW(139.8, 35.7);
printf("L=%.4f,%.4f\n",@L);
printf("T=%.4f,%.4f\n",@T);
my $dist = great_circle_distance(@L, @T);
# About 9600 km.
printf("dist=%.4f (%.0f km)\n",$dist,6378*$dist);
my $rad = great_circle_direction(@L, @T);
# About 0.547 or 0.174 pi.
printf("rad=%.3f (%.3f pi, %.1f deg)\n",$rad,$rad/pi,rad2deg($rad));
# What's this, we don't end up in Tokyo using the calculated $rad and $dist?
my @D=great_circle_destination(@L,$rad,$dist);
printf("D=%.4f,%.4f (%.4f) %.1f,%.1f\n",@D,rad2deg($D[0]),rad2deg($D[1]));
# It would seem that the 90 degree conversion done in NESW is neglected?
Show quoted text
---- output ----
L=-0.0087,0.6754
T=2.4400,0.9477
dist=1.5060 (9605 km)
rad=0.547 (0.174 pi, 31.3 deg)
D=2.4400,0.6231 (2.7006) 139.8,35.7
--
/* * * Otto J. Makela <om@iki.fi> * * * * * * * * * * * * * * * */
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