Calculate distance between all Lat-Lons saved in GPX file.

gpx_distance.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

module GpxDistance
  def calc_gpx_distance(gpx_file)
    gpx = File.open(gpx_file) { |f| f.read }
    latlons = []

    gpx.each_line { |line| latlons << [$1.to_f, $2.to_f] if line =~ /<trkpt lat="([0-9.]+)" lon="([0-9.]+)">/ }

    distance = calc_distance(latlons)
    distance / 1000 # kilometers
  end

  private
  def calc_distance(latlons)
    latlons.map! { |latlon| deg_to_rad(latlon) }
    distance = (0...latlons.length - 1).inject(0) { |dist, i| dist + hubeny(latlons[i], latlons[i + 1]) }
    distance # meters
  end

  def deg_to_rad(latlng)
    latlng.map { |deg| deg * Math::PI / 180 }
  end

  # http://yamadarake.jp/trdi/report000001.html
  # WGS84 (GPS)
  A = 6378137.000
  B = 6356752.314245

  def hubeny(latlng_1, latlng_2)
    pow_e = 1 - B ** 2 / A ** 2

    ave = (latlng_1[0] + latlng_2[0]) / 2
    dp = latlng_1[0] - latlng_2[0]
    dr = latlng_1[1] - latlng_2[1]
    sin_ave = Math.sin(ave)
    cos_ave = Math.cos(ave)
    w = Math.sqrt(1 - pow_e * sin_ave ** 2)
    m = A * (1 - pow_e) / w ** 3
    n = A / w

    distance = Math.sqrt((m * dp) ** 2 + (n * cos_ave * dr) ** 2)
    distance #meters
  end
end


include GpxDistance

exit 1 if ARGV.length < 1
gpx_file = ARGV[0]
distance = calc_gpx_distance(gpx_file)

puts sprintf("%.3f km", distance)

Nor sure this is still supported (it rocks, BTW...) but the matches in line 8 should be

([0-9.\-]+)

...to cater for minus lat/longs - my files (in the UK) have minuses in them.