> > 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 >
Thank you Jim. Your module seems to be the solution I am looking for. Just one question. If the two sets of coordinates are the same I was expecting the distance to be 0 miles. Instead I get: 2.19558883102012e-013 For the following example. #!/usr/bin/perl use strict; use warnings; use feature qw(say); use Geo::Ellipsoid; my $lat1 = 39.316858; my $lat2 = 39.316858; my $lon1 = -94.963194; my $lon2 = -94.963194; my $ellipsoid = Geo::Ellipsoid->new(units=>'degrees', dist=>'miles'); say $ellipsoid->range($lat1,$lon1,$lat2,$lon2); If it is the expected outcome would you please explain why? Thank you, Chris -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
