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Distance computations between pairs of coordinates are complicated by the fact
that the earth is not flat.  A good approximation is found in
47 CFR Sec. 73.208 which is used by radio engineers.
 
    Sec. 73.208 Reference points and distance computations.
 
      (c) The method given in this paragraph shall be used to compute
    the distance between two reference points, except that, for
    computation of distance involving stations in Canada and Mexico,
    the method for distance computation specified in the applicable
    international agreement shall be used instead.  The method set
    forth in this paragraph is valid only for distances not exceeding
    475 km (295 miles).
      (1) Convert the latitudes and longitudes of each reference point
    from degree-minute-second format to degree-decimal format by
    dividing minutes by 60 and seconds by 3600, then adding the results
    to degrees.
      (2) Calculate the middle latitude between the two reference
    points by averaging the two latitudes as follows:
    ML=(LAT1 (INFERIOR dd)+LAT2 (INFERIOR dd)) () 2
      (3) Calculate the number of kilometers per degree latitude
    difference for the middle latitude calculated in paragraph (c)(2)
    as follows:
    KPD (INFERIOR lat)=111.13209-0.56605 cos(2ML)+0.00120 cos(4ML)
      (4) Calculate the number of kilometers per degree longitude
    difference for the middle latitude calculated in paragraph (c)(2)
    as follows:
    KPD (INFERIOR lon)=111.41513 cos(ML)-0.09455 cos(3ML)+0.00012
        cos(5ML)
      (5) Calculate the North-South distance in kilometers as follows:
    NS=KPD (INFERIOR lat) (LAT1 (INFERIOR dd)-LAT2 (INFERIOR dd))
      (6) Calculate the East-West distance in kilometers as follows:
    EW=KPD (INFERIOR lon) (LON1 (INFERIOR dd)-LON2 (INFERIOR dd))
      (7) Calculate the distance between the two reference points by
    taking the square root of the sum of the squares of the East-West
    and North-South distances as follows:
    DIST=(NS (SUPERSCRIPT 2+)EW (SUPERSCRIPT 2)) (SUPERSCRIPT 0.5)
      (8) Round the distance to the nearest kilometer.
      (9) Terms used in this section are defined as follows:
      (i) LAT1 (INFERIOR dd) and LON1 (INFERIOR dd)=the coordinates of
    the first reference point in degree-decimal format.
      (ii) LAT2 (INFERIOR dd) and LON2 (INFERIOR dd)=the coordinates of
    the second reference point in degree-decimal format.
      (iii) ML=the middle latitude in degree-decimal format.
      (iv) KPD (INFERIOR lat)=the number of kilometers per degree of
    latitude at a given middle latitude.
      (v) KPD (INFERIOR lon)=the number of kilometers per degree of
    longitude at a given middle latitude.
      (vi) NS=the North-South distance in kilometers.
      (vii) EW=the East-West distance in kilometers.
      (viii) DIST=the distance between the two reference points, in
    kilometers.
 
Simple, eh?
 
I have placed a Q-BASIC Text file, which is simple txt that will run on
Q-BASIC with this very formula on our server, which you may access
at:
     http://www.jmu.edu/wmra/dandb.txt
 
enjoy.
 
 
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Bill Fawcett                                 [log in to unmask]
James Madison University                       adm_wfawcett@jmuvax (bitnet)
821 S. Main Street, Harrisonburg, VA 22807           (703) 568-3809 voice
N. Lat. 38-26-27   W. Long. 78-52-33                 (703) 568-3814 fax
           - -  Virginia- The home of Matthew Fontaine Maury  - -
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formula is found on