dist.cpp

/*dist.cpp*/

//
// Computes the distance between 2 positions, given in
// (latitude, longitude) coordinates.
// 
// Mark Fortes
// Northwestern University
// CS 211: Winter 2023
// 

#include <iostream>
#include <cmath>

#include "dist.h"

using namespace std;


//
// DistBetween2Points
//
// Returns the distance in miles between 2 points (lat1, long1) and 
// (lat2, long2). Latitudes are positive above the equator and 
// negative below; longitudes are positive heading east of Greenwich 
// and negative heading west. Example: Chicago is (41.88, -87.63).
//
// NOTE: may get slightly different results depending on which 
// (lat, long) pair is passed as the first parameter.
// 
double distBetween2Points(double lat1, double long1, double lat2, double long2)
{
  //
  // Reference: http://www8.nau.edu/cvm/latlon_formula.html
  //
  double PI = 3.14159265;
  double earth_rad = 3963.1;  // statue miles:

  double lat1_rad = lat1 * PI / 180.0;
  double long1_rad = long1 * PI / 180.0;
  double lat2_rad = lat2 * PI / 180.0;
  double long2_rad = long2 * PI / 180.0;

  double dist = earth_rad * acos(
    (cos(lat1_rad) * cos(long1_rad) * cos(lat2_rad) * cos(long2_rad))
    +
    (cos(lat1_rad) * sin(long1_rad) * cos(lat2_rad) * sin(long2_rad))
    +
    (sin(lat1_rad) * sin(lat2_rad))
  );

  return dist;
}