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Re: Alternatives To Geo::Distance (hack)

by tye (Sage)
on Oct 21, 2010 at 19:22 UTC ( #866624=note: print w/replies, xml ) Need Help??


in reply to Alternatives To Geo::Distance

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)

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%.

- tye        

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Re^2: Alternatives To Geo::Distance (hack)
by BrowserUk (Pope) on Oct 22, 2010 at 09:59 UTC

    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)

    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.
      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.

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