On Aug 29, 2012, at 2:08 PM, Chris Stinemetz wrote: > Hello List, > > I'm tyring to find the distance in miles between two sets of > coordinates by using the module Math::Trig > > I'm expecting the return distance to be around 16.91 miles. > > Any help is greatly appriciated. > > Chris > > #!/usr/bin/perl > > use strict; > use warnings; > use Math::Trig qw(pi great_circle_distance); > > my $LAT1 = 39.316858; > my $LAT2 = 39.243556; > my $LONG1 = -94.963194; > my $LONG2 = -94.6617; > print great_circle_distance($LONG1, pi/2 - $LAT1, $LONG2, pi/2 - $LAT2);
The Math::Trig routines all work with radians. Therefore, you are going to have to convert your locations from degrees to radians. You can use the Math::Trig::deg2rad function. Note that pi/2 is radians, so you are subtracting degrees from radians, which never works. The great_circle_distance function returns radians by default, so you are going to have to convert the return values into miles using the approximate radius of the earth in miles (~3963mi). Note that the earth is not a perfect sphere, so it doesn't have just one radius, but varies from pole to equator. If you want to do latitude, longitude, and distance calculations, there are modules available from CPAN. I can mention Geo::Distance, GIS::Distance, and Geo::Ellipsoid (which I wrote). These modules take into account the fact that the earth not perfectly spherical. Here is your program modified to compare results from Geo::Ellipsoid and Math::Trig::great_circle_distance. #!/usr/bin/perl use strict; use warnings; use feature qw(say); use Math::Trig qw(pi great_circle_distance deg2rad); use Geo::Ellipsoid; my $earth_meters = 6378137.0; my $meters_per_mile = 1609.34; my $earth_miles = $earth_meters / $meters_per_mile; say "The radius of the earth is $earth_miles miles"; my $lat1 = 39.316858; my $lat2 = 39.243556; my $lon1 = -94.963194; my $lon2 = -94.6617; my $latrad1 = deg2rad($lat1); my $latrad2 = deg2rad($lat2); my $lonrad1 = deg2rad($lon1); my $lonrad2 = deg2rad($lon2); my $dist = great_circle_distance($lonrad1, pi/2 - $latrad1, $lonrad2, pi/2 - $latrad2); say $dist * $earth_meters / $meters_per_mile; my $ellipsoid = Geo::Ellipsoid->new(units=>'degrees', dist=>'miles'); say $ellipsoid->range($lat1,$lon1,$lat2,$lon2); Results: The radius of the earth is 3963.20044241739 miles 16.9202528447011 16.9368500188459 -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
