Just for reference, here is the quick and dirty implementation I threw together after consulting several pages at Wikipedia:

    sub acos { atan2( sqrt(1-$_[0]*$_[0]), $_[0] ) }
    sub asin { atan2( $_[0], sqrt(1-$_[0]*$_[0]) ) }
    my $pi= atan2(0,-1);
    my @c= ( 33.943603, -118.408189, 39.17965, -76.668824 );
    my $lat1= $c[0]/180*$pi;
    my $lat2= $c[2]/180*$pi;
    my $dlong= ($c[1]-$c[3])/180*$pi;
    my $ang= acos( sin($lat1)*sin($lat2)
        + cos($lat1)*cos($lat2)*cos($dlong) );
    my $max= $ang * 3_963.19059;
    my $min= $ang * 3_949.90257;
    printf "%.1f .. %.1f miles (%.2f range)\n", $min, $max, $max-$min;
    my $h1= sin(($lat1-$lat2)/2);
    my $h2= sin($dlong/2);
    $ang= 2*asin( sqrt( $h1*$h1 + cos($lat1)*cos($lat2)*$h2*$h2 ) );
    $max= $ang * 3_963.19059;
    $min= $ang * 3_949.90257;
    printf "%.1f .. %.1f miles (%.2f range)\n", $min, $max, $max-$min;
__END__
2318.6 .. 2326.4 miles (7.80 range)
2318.6 .. 2326.4 miles (7.80 range)
[download]

And if somebody tells you that a >10% error is due to Earth being an oblate spheroid, tell them that such a discrepancy would be less than 0.34%.

It seems to rapidly screw up as you move north.

The distance from (0,0)-(10,10) should be the same as from (80,0)-(90,10) as shown by the Geo::Distance output. Or should it?

[0,0][10,10]
geo: 974.731395416589
972.5 .. 975.7 miles (3.27 range)
972.5 .. 975.7 miles (3.27 range)
[10,0][20,10]
geo: 974.731395416589
957.7 .. 960.9 miles (3.22 range)
957.7 .. 960.9 miles (3.22 range)
[20,0][30,10]
geo: 974.731395416589
929.4 .. 932.5 miles (3.13 range)
929.4 .. 932.5 miles (3.13 range)
[30,0][40,10]
geo: 974.731395416589
889.9 .. 892.9 miles (2.99 range)
889.9 .. 892.9 miles (2.99 range)
[40,0][50,10]
geo: 974.731395416589
842.7 .. 845.5 miles (2.84 range)
842.7 .. 845.5 miles (2.84 range)
[50,0][60,10]
geo: 974.731395416589
792.8 .. 795.5 miles (2.67 range)
792.8 .. 795.5 miles (2.67 range)
[60,0][70,10]
geo: 974.731395416589
746.2 .. 748.7 miles (2.51 range)
746.2 .. 748.7 miles (2.51 range)
[70,0][80,10]
geo: 974.731395416589
709.6 .. 712.0 miles (2.39 range)
709.6 .. 712.0 miles (2.39 range)
[80,0][90,10]
geo: 974.731395416589
689.4 .. 691.7 miles (2.32 range)
689.4 .. 691.7 miles (2.32 range)
[download]

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

RIP an inspiration; A true Folk's Guy

The distance should go down closer to the pole. (90,10) and (90,0) are the same point.

If you start at the north pole and walk one mile to the south and then one mile to the west you are still one mile to the south of the north pole. At the equator you will get a hypotenuse.

Speaking as the author of Geo-Distance-XS, I consider it to be actively developed. Even though Geo-Distance might be considered decommissioned by it's author, he probably will accept patches via its github repo. As will I for Geo::Distance::XS at its its repo.

A good reason to use Geo::Distance::XS:

---- [ Formula: hsin ] ------------------------------------
perl      - distance from BWI to LAX: 2324.06319758555 miles
xs        - distance from BWI to LAX: 2324.06319758555 miles
gis::fast - distance from BWI to LAX: 2324.06319758555 miles

Benchmark: running gis::fast, perl, xs for at least 1 CPU seconds...
 gis::fast:  1 wallclock secs ( 1.05 usr +  0.01 sys =  1.06 CPU) @ 23
+866.04/s (n=25298)
      perl:  1 wallclock secs ( 1.05 usr +  0.00 sys =  1.05 CPU) @ 78
+019.05/s (n=81920)
        xs:  2 wallclock secs ( 1.12 usr + -0.01 sys =  1.11 CPU) @ 12
+45236.94/s (n=1382213)
               Rate gis::fast      perl        xs
gis::fast   23866/s        --      -69%      -98%
perl        78019/s      227%        --      -94%
xs        1245237/s     5118%     1496%        --

---- [ Formula: polar ] ------------------------------------
perl      - distance from BWI to LAX: 2652.59252292455 miles
xs        - distance from BWI to LAX: 2652.59252292455 miles
gis::fast - distance from BWI to LAX: 2652.59252292455 miles

Benchmark: running gis::fast, perl, xs for at least 1 CPU seconds...
 gis::fast:  1 wallclock secs ( 1.08 usr +  0.00 sys =  1.08 CPU) @ 18
+962.96/s (n=20480)
      perl:  1 wallclock secs ( 1.07 usr +  0.00 sys =  1.07 CPU) @ 80
+736.45/s (n=86388)
        xs:  2 wallclock secs ( 1.14 usr +  0.00 sys =  1.14 CPU) @ 15
+09051.75/s (n=1720319)
               Rate gis::fast      perl        xs
gis::fast   18963/s        --      -77%      -99%
perl        80736/s      326%        --      -95%
xs        1509052/s     7858%     1769%        --

---- [ Formula: cos ] ------------------------------------
perl      - distance from BWI to LAX: 2324.06319758555 miles
xs        - distance from BWI to LAX: 2324.06319758555 miles
gis::fast - distance from BWI to LAX: 2324.06319758555 miles

Benchmark: running gis::fast, perl, xs for at least 1 CPU seconds...
 gis::fast:  1 wallclock secs ( 1.07 usr +  0.00 sys =  1.07 CPU) @ 23
+642.99/s (n=25298)
      perl:  1 wallclock secs ( 1.06 usr +  0.00 sys =  1.06 CPU) @ 77
+282.08/s (n=81919)
        xs:  0 wallclock secs ( 1.00 usr +  0.00 sys =  1.00 CPU) @ 13
+10719.00/s (n=1310719)
               Rate gis::fast      perl        xs
gis::fast   23643/s        --      -69%      -98%
perl        77282/s      227%        --      -94%
xs        1310719/s     5444%     1596%        --

---- [ Formula: gcd ] ------------------------------------
perl      - distance from BWI to LAX: 0 miles
xs        - distance from BWI to LAX: 2324.06319758555 miles
gis::fast - distance from BWI to LAX: 0 miles

Benchmark: running gis::fast, perl, xs for at least 1 CPU seconds...
 gis::fast:  1 wallclock secs ( 1.07 usr +  0.00 sys =  1.07 CPU) @ 18
+270.09/s (n=19549)
      perl:  2 wallclock secs ( 1.07 usr +  0.00 sys =  1.07 CPU) @ 73
+080.37/s (n=78196)
        xs:  1 wallclock secs ( 1.05 usr +  0.01 sys =  1.06 CPU) @ 12
+98354.72/s (n=1376256)
               Rate gis::fast      perl        xs
gis::fast   18270/s        --      -75%      -99%
perl        73080/s      300%        --      -94%
xs        1298355/s     7006%     1677%        --

---- [ Formula: mt ] ------------------------------------
perl      - distance from BWI to LAX: 2324.06319758555 miles
xs        - distance from BWI to LAX: 2324.06319758555 miles
gis::fast - distance from BWI to LAX: 2324.06319758555 miles

Benchmark: running gis::fast, perl, xs for at least 1 CPU seconds...
 gis::fast:  1 wallclock secs ( 1.12 usr +  0.01 sys =  1.13 CPU) @ 17
+300.00/s (n=19549)
      perl:  1 wallclock secs ( 1.06 usr +  0.00 sys =  1.06 CPU) @ 67
+621.70/s (n=71679)
        xs:  2 wallclock secs ( 1.07 usr +  0.01 sys =  1.08 CPU) @ 12
+74311.11/s (n=1376256)
               Rate gis::fast      perl        xs
gis::fast   17300/s        --      -74%      -99%
perl        67622/s      291%        --      -95%
xs        1274311/s     7266%     1784%        --

---- [ Formula: tv ] ------------------------------------
perl      - distance from BWI to LAX: 2328.95218785171 miles
xs        - distance from BWI to LAX: 2324.51147636132 miles
gis::fast - distance from BWI to LAX: 2328.95218785171 miles

Benchmark: running gis::fast, perl, xs for at least 1 CPU seconds...
 gis::fast:  2 wallclock secs ( 1.09 usr +  0.01 sys =  1.10 CPU) @ 21
+720.91/s (n=23893)
      perl:  1 wallclock secs ( 1.09 usr +  0.00 sys =  1.09 CPU) @ 16
+439.45/s (n=17919)
        xs:  2 wallclock secs ( 1.05 usr +  0.00 sys =  1.05 CPU) @ 77
+1011.43/s (n=809562)
              Rate      perl gis::fast        xs
perl       16439/s        --      -24%      -98%
gis::fast  21721/s       32%        --      -97%
xs        771011/s     4590%     3450%        --
[download]

#!/usr/bin/env perl
use strict;
use warnings;

use Benchmark qw(cmpthese timethese);
use Geo::Distance::XS;
use GIS::Distance;

# When benchmarking, need to have it call import/unimport before the
# code is executed.
my $orig_timethis_sub = \&Benchmark::timethis;
{
    no warnings 'redefine';
    *Benchmark::timethis = sub {
        my $sub = ('perl' eq $_[2] ? 'un' : '') . 'import';
        Geo::Distance::XS->$sub();
        $orig_timethis_sub->(@_);
    };
}

# Lon, Lat
my @coord = (-76.668851, 39.179689, -118.408618, 33.943532);

my $geo = Geo::Distance->new;
my $gis = GIS::Distance->new;

my %gis_formula = (
    hsin  => 'Haversine',
    polar => 'Polar',
    cos   => 'Cosine',
    gcd   => 'GreatCircle',
    mt    => 'MathTrig',
    tv    => 'Vincenty',
);

sub geo {
    my $d = $geo->distance(mile => @coord);
}
sub gis {
    my $d = $gis->distance(@coord[ 1, 0, 3, 2 ]);
    return $d->mile;
}

for my $formula (qw(hsin polar cos gcd mt tv)) {
    print "---- [ Formula: $formula ] --------------------------------
+----\n";

    $geo->formula($formula);
    $gis->formula($gis_formula{$formula});

    Geo::Distance::XS->unimport;
    printf "perl      - distance from BWI to LAX: %s miles\n", geo();
    Geo::Distance::XS->import;
    printf "xs        - distance from BWI to LAX: %s miles\n", geo();
    printf "gis::fast - distance from BWI to LAX: %s miles\n", gis();
    print "\n";

    my $benchmarks = timethese - 1, {
        perl        => \&geo,
        xs          => \&geo,
        'gis::fast' => \&gis,
    };

    cmpthese $benchmarks;
    print "\n";
}
[download]

gray,
...he probably will accept patches via

I have emailed the author. I would like to offer a patch but I am not sure what the problem is. I was in a hurry to get my project complete so I could go to sleep.

A good reason to use Geo::Distance::XS

First, thanks! I admit that I didn't try it for a few reasons. The first is that I assumed one was just an XS implementation of the other to include the bug. The second reason is that in the environment where this needed to run, XS is not an easy option. Without going into a lot of detail - local politics have created technical hurdles I didn't want to jump through (I was tired). It is also the reason I didn't use GIS::Distance. I was pretty sure (and you confirmed) that it produces correct results but the litany of dependencies without an internet connection was unreasonable.

I am happy that there are working solutions out there. I guess after reflecting on my lamentation, what I really should have asked is: Does anyone know of a Geo::Distance::Lite that works?

Regarding your benchmark. First, I suspect you didn't "You can stick with the pure Perl version by setting the GEO_DISTANCE_PP environment variable before using this module" This is because Geo::Distance gave the correct answer which it I know it doesn't (the point of this thread). Second, it would only be fair to add tye's version which avoids the whole OO overhead.

Cheers - L~R

Regarding your benchmark. First, I suspect you didn't "You can stick with the pure Perl version by setting the GEO_DISTANCE_PP environment variable before using this module" This is because Geo::Distance gave the correct answer which it I know it doesn't (the point of this thread).

$ENV{GEO_DISTANCE_PP} just triggers Geo::Distance::XS->unimport(), which my benchmark script calls directly. I also checked the results by hiding Geo::Distance::XS with Test-Without-Module and they were consistent. Note also the results for the 'gcd' formula- both Geo::Distance and GIS::Distance::Fast failed, whereas Geo::Distance::XS produced a reasonable result. Perhaps if you posted your test script we could dig further.

#!/usr/bin/perl

use strict;
use warnings;
use Geo::Ellipsoid;

my @ellipsoids = (
    'AIRY',
    'AIRY-MODIFIED',
    'AUSTRALIAN',
    'BESSEL-1841',
    'CLARKE-1880',
    'EVEREST-1830',
    'EVEREST-MODIFIED',
    'FISHER-1960',
    'FISHER-1968',
    'GRS80',
    'HOUGH-1956',
    'HAYFORD',
    'IAU76',
    'KRASSOVSKY-1938',
    'NAD27',
    'NWL-9D',
    'SOUTHAMERICAN-1969',
    'SOVIET-1985',
    'WGS72',
    'WGS84'
);

foreach my $ellipsoid(@ellipsoids) {
    my $geo = Geo::Ellipsoid->new(
       ellipsoid => $ellipsoid, 
       units     => 'degrees',
       distance_units  => 'mile',
       longitude => 1,
       bearing   => 1,
   );
    my @origin = ( 37.619002, -122.374843 );
    my @dest   = ( 33.942536, -118.408074 );
    my ( $range,  $bearing ) = $geo->to( @origin, @dest );
    my ($lat, $lon) = $geo->at( @origin, 2000, 45.0);
    my ($x, $y)     = $geo->displacement( @origin, $lat, $lon );
    my @pos         = $geo->location( $lat, $lon, $x, $y ); 
    print my $dist  = $geo->range( @origin, @dest ), "\n";
}
[download]