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Lat/Long distance calculator

by jcwren (Prior)
on Nov 07, 2000 at 20:53 UTC ( #40354=sourcecode: print w/ replies, xml ) Need Help??

Category: Miscellaneous
Author/Contact Info jcwren@jcwren.com
Description: This code takes a latitude/longtitude pair and returns the distance and heading between them. As a practical (hah!) demonstration, it calculates how far your PM T-shirt has to travel to get from vroom to you (assuming you change the location, otherwise it's vroom to jcwren)
#!/usr/local/bin/perl -w

use strict;
use POSIX qw(atan acos floor);

#
#  Use www.mapblast.com, or your coordinates from the MonkMap page if 
+you're already there.
#  Latitude and longtitude are expressed in decimal notation.  North a
+nd east values are
#  positive, South and west are negative.
#
{
   my @location_of_me    = qw(34.172500 -84.001667);  # latitude=34.17
+2500, longitude=-84.001667 of jcwren
   my @location_of_vroom = qw(42.763333 -86.110556);  # latitude=42.76
+3333, longitude=-86.110556 of vroom

   print sprintf ("\nMy T-shirt has to travel %0.f miles, on a heading
+ of %.1f degrees, to get from vroom to me\n\n",
                  range_and_bearing (@location_of_vroom, @location_of_
+me));
}

#
#  Returns range (in miles), and angle (relative to $latitude1/$longti
+tude1)
#
#  Uses basic great circle route calculation.  Output compares favorab
+ly with www.mapblast.com
#  www.mapquest.com, and Delorme Street Atlas.  Minor deviations since
+ the earth is not a true
#  sphere, but bulges slighty at the equator.  Accurate enough for com
+mon distance calculations, 
#  do not use to calculate fuel usage for cruise missiles targetting (
+0.2% error seems to be 
#  typical worst case, though)
#
sub range_and_bearing
{
   my ($latitude1, $longitude1, $latitude2, $longitude2) = @_;

   my $pi = 3.1415926535897;
   my $radToDeg = 180.0 / $pi;
   my $degToRad = $pi / 180.0;
   my $earthRadius = 3958.9;              # Use 3958.9=miles, 6371.0=K
+m;

   my $distance = 0;
   my $azimuth = 0;
   my $beta = 0;
   my $cosBeta = 0;
   my $cosAzimuth = 0;

   $latitude1  = $latitude1  * $degToRad;
   $longitude1 = $longitude1 * $degToRad;
   $latitude2  = $latitude2  * $degToRad;
   $longitude2 = $longitude2 * $degToRad;

   if (abs ($latitude1) < 90.0)
   {
      $cosBeta = (sin ($latitude1) * sin ($latitude2)) + ((cos ($latit
+ude1) * cos ($latitude2)) * cos ($longitude2 - $longitude1));
   
      if ($cosBeta >= 1.0)
      {
         return (0.0, 0.0);
      }
   
      #
      #  Antipodes  (return miles, 0 degrees)
      #
      if ($cosBeta <= -1.0)
      {
         return (floor ($earthRadius * $pi * 100.0) / 100.0, 0.0);
      }
   
      $beta = acos ($cosBeta);
      $distance = $beta * $earthRadius;
      $cosAzimuth = (sin ($latitude2) - sin ($latitude1) * cos ($beta)
+) / (cos ($latitude1) * sin ($beta));
   
      if ($cosAzimuth >= 1.0)
      {
         $azimuth = 0.0;
      }
      elsif ($cosAzimuth <= -1.0)
      {
         $azimuth = 180.0;
      }
      else
      {
         $azimuth = acos ($cosAzimuth) * $radToDeg;
      }
   
      if (sin ($longitude2 - $longitude1) < 0.0)
      {
         $azimuth = 360.0 - $azimuth;
      }
   
      return (floor ($distance * 100.0) / 100.0, floor ($azimuth * 100
+.0) / 100.0);
   }

   #
   #  If P1 Is North Or South Pole, Then Azimuth Is Undefined
   #
   if (sgn ($latitude1) == sgn ($latitude2))
   {
      $distance = $earthRadius * ($pi / 2 - abs ($latitude2));
   }
   else
   {
      $distance = $earthRadius * ($pi / 2 + abs ($latitude2));
   }

   return (floor ($distance * 100.0) / 100.0, 0.0);
}

#
#  Why is there no intrinsic sign function in Perl?
#
sub sgn
{
   return $_[0] == 0 ? 0 : $_[0] < 0 ? -1 : 1;
}

Comment on Lat/Long distance calculator
Download Code
RE: Lat/Long distance calculator
by Fastolfe (Vicar) on Nov 07, 2000 at 20:59 UTC
    Also see Math::Trig's great_circle_distance function. From the documentation:
    # To calculate the distance between London (51.3N 0.5W) # and Tokyo (35.7N 139.8E) in kilometers: use Math::Trig qw(great_circle_distance deg2rad); # Notice the 90 - latitude: phi zero is at the North Pole. @L = (deg2rad(-0.5), deg2rad(90 - 51.3)); @T = (deg2rad(139.8),deg2rad(90 - 35.7)); $km = great_circle_distance(@L, @T, 6378);
      Typical. I searched CPAN for latitude, longitude, Geo, and a few others, but not Math::Trig. Hardly an intuitive place to look.

      --Chris

      e-mail jcwren
        I agree. I only happened to remember it because I had examined Math::Trig for unrelated functions in the past and noticed it was in there.
RE: Lat/Long distance calculator
by chromatic (Archbishop) on Nov 08, 2000 at 10:02 UTC
      Hmm, I smell rewrite from cgi? That bit may have had a bunch of html and commas around it. =)

      --
      $you = new YOU;
      honk() if $you->love(perl)

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