distance calculation code

## {{{ http://code.activestate.com/recipes/576779/ (r2)
#coding:UTF-8
"""
  Python implementation of Haversine formula
  Copyright (C) <2009>  Bartek Górny <bartek@gorny.edu.pl>

This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
"""

import math

def recalculate_coordinate(val,  _as=None):
  """
    Accepts a coordinate as a tuple (degree, minutes, seconds)
    You can give only one of them (e.g. only minutes as a floating point number) 
    and it will be duly recalculated into degrees, minutes and seconds.
    Return value can be specified as 'deg', 'min' or 'sec'; default return value is 
    a proper coordinate tuple.
  """
  deg,  min,  sec = val
  # pass outstanding values from right to left
  min = (min or 0) + int(sec) / 60
  sec = sec % 60
  deg = (deg or 0) + int(min) / 60
  min = min % 60
  # pass decimal part from left to right
  dfrac,  dint = math.modf(deg)
  min = min + dfrac * 60
  deg = dint
  mfrac,  mint = math.modf(min)
  sec = sec + mfrac * 60
  min = mint
  if _as:
    sec = sec + min * 60 + deg * 3600
    if _as == 'sec': return sec
    if _as == 'min': return sec / 60
    if _as == 'deg': return sec / 3600
  return deg,  min,  sec

def points2distance(start,  end):
  """
    Calculate distance (in kilometers) between two points given as (long, latt) pairs
    based on Haversine formula (http://en.wikipedia.org/wiki/Haversine_formula).
    Implementation inspired by JavaScript implementation from 
    http://www.movable-type.co.uk/scripts/latlong.html
    Accepts coordinates as tuples (deg, min, sec), but coordinates can be given 
    in any form - e.g. can specify only minutes:
    (0, 3133.9333, 0) 
    is interpreted as 
    (52.0, 13.0, 55.998000000008687)
    which, not accidentally, is the lattitude of Warsaw, Poland.
  """
  start_long = math.radians(recalculate_coordinate(start[0],  'deg'))
  start_latt = math.radians(recalculate_coordinate(start[1],  'deg'))
  end_long = math.radians(recalculate_coordinate(end[0],  'deg'))
  end_latt = math.radians(recalculate_coordinate(end[1],  'deg'))
  d_latt = end_latt - start_latt
  d_long = end_long - start_long
  a = math.sin(d_latt/2)**2 + math.cos(start_latt) * math.cos(end_latt) * math.sin(d_long/2)**2
  c = 2 * math.atan2(math.sqrt(a),  math.sqrt(1-a))
  return 6371 * c

if __name__ == '__main__':
 warsaw = ((22,  0,  30),  (52, 13, 56))
 cracow = ((19, 56, 18),  (50, 3, 41))
 print points2distance(warsaw,  cracow)
## end of http://code.activestate.com/recipes/576779/ }}}

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