use strict;

sub distance {
    my ( $lat1, $lon1, $lat2, $lon2, $unit ) = @_;
    my $theta = $lon1 - $lon2;
    my $dist
        = sin( deg2rad($lat1) ) * sin( deg2rad($lat2) )
        + cos( deg2rad($lat1) ) * cos( deg2rad($lat2) ) *
        cos( deg2rad($theta) );
    $dist = acos($dist);
    $dist = rad2deg($dist);
    my $miles = $dist * 60 * 1.1515;
    $unit = uc $unit;
    if ( $unit eq "K" ) {
        return ( $miles * 1.609344 );
    } ## end if ( $unit eq "K" )
    elsif ( $unit eq "N" ) {
        return ( $miles * 0.8684 );
    } ## end elsif ( $unit eq "N" )
    else {
        return $miles;
    } ## end else [ if ( $unit eq "K" )
} ## end sub distance

sub acos { atan2( sqrt( 1 - $_[0] * $_[0] ), $_[0] ) }

sub deg2rad { $_[0] * 0.0174532925 }

sub rad2deg { $_[0] * 57.2957795 }