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Diffstat (limited to 'contrib/perl5/lib/Math/Trig.pm')
| -rw-r--r-- | contrib/perl5/lib/Math/Trig.pm | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/contrib/perl5/lib/Math/Trig.pm b/contrib/perl5/lib/Math/Trig.pm index b7b5d5d..924286d 100644 --- a/contrib/perl5/lib/Math/Trig.pm +++ b/contrib/perl5/lib/Math/Trig.pm @@ -314,9 +314,11 @@ known as the I<radial> coordinate. The angle in the I<xy>-plane coordinate. The angle from the I<z>-axis is B<phi>, also known as the I<polar> coordinate. The `North Pole' is therefore I<0, 0, rho>, and the `Bay of Guinea' (think of the missing big chunk of Africa) I<0, -pi/2, rho>. +pi/2, rho>. In geographical terms I<phi> is latitude (northward +positive, southward negative) and I<theta> is longitude (eastward +positive, westward negative). -B<Beware>: some texts define I<theta> and I<phi> the other way round, +B<BEWARE>: some texts define I<theta> and I<phi> the other way round, some texts define the I<phi> to start from the horizontal plane, some texts use I<r> in place of I<rho>. @@ -374,13 +376,25 @@ by importing the C<great_circle_distance> function: use Math::Trig 'great_circle_distance' - $distance = great_circle_distance($theta0, $phi0, $theta1, $phi, [, $rho]); + $distance = great_circle_distance($theta0, $phi0, $theta1, $phi1, [, $rho]); The I<great circle distance> is the shortest distance between two points on a sphere. The distance is in C<$rho> units. The C<$rho> is optional, it defaults to 1 (the unit sphere), therefore the distance defaults to radians. +If you think geographically the I<theta> are longitudes: zero at the +Greenwhich meridian, eastward positive, westward negative--and the +I<phi> are latitudes: zero at the North Pole, northward positive, +southward negative. B<NOTE>: this formula thinks in mathematics, not +geographically: the I<phi> zero is at the North Pole, not at the +Equator on the west coast of Africa (Bay of Guinea). You need to +subtract your geographical coordinates from I<pi/2> (also known as 90 +degrees). + + $distance = great_circle_distance($lon0, pi/2 - $lat0, + $lon1, pi/2 - $lat1, $rho); + =head1 EXAMPLES To calculate the distance between London (51.3N 0.5W) and Tokyo (35.7N @@ -394,8 +408,8 @@ To calculate the distance between London (51.3N 0.5W) and Tokyo (35.7N $km = great_circle_distance(@L, @T, 6378); -The answer may be off by up to 0.3% because of the irregular (slightly -aspherical) form of the Earth. +The answer may be off by few percentages because of the irregular +(slightly aspherical) form of the Earth. =head1 BUGS |
