From: Earl F. Glynn (73257.3527@CompuServe.COM)
Subject: Re: how to determine distance between lat/long points?
Newsgroups: sci.math
Date: 1996/01/29


  FUNCTION arcos (x:  REAL):  REAL;
  BEGIN
    IF   x = 1.0
    THEN arcos := 0.0
    ELSE
      IF   x = 0.0
      THEN arcos := 0.5*pi
      ELSE arcos := 0.5*pi - ARCTAN( x / SQRT(1.0 - x*x) )
  END {arcos};

  FUNCTION GreatCircle (lat1,lng1, lat2,lng2:  REAL {degrees}):
    REAL {miles};
  VAR
    RadiansPerDegree:  REAL;
  BEGIN
    RadiansPerDegree := pi/180;
    lat1 := RadiansPerDegree * lat1;
    lng1 := RadiansPerDegree * lng1;
    lat2 := RadiansPerDegree * lat2;
    lng2 := RadiansPerDegree * lng2;
    GreatCircle := 3956.67 {miles or 6367.650 km} *
      arcos( SIN(lat1)*SIN(lat2) +
      COS(lat1)*COS(lat2)*COS(lng1-lng2) )
  END {GreatCircle};

--
Earl F. Glynn
Staff Scientist
E for M Corporation, Cardiology Products Division
73257.3527@compuserve.com