Calculate distance between two GPS point

haversine.ino

// Calculate distance between two points
float distanceCoordinates(float flat1, float flon1, float flat2, float flon2) {

  // Variables
  float dist_calc=0;
  float dist_calc2=0;
  float diflat=0;
  float diflon=0;

  // Calculations
  diflat  = radians(flat2-flat1);
  flat1 = radians(flat1);
  flat2 = radians(flat2);
  diflon = radians((flon2)-(flon1));

  dist_calc = (sin(diflat/2.0)*sin(diflat/2.0));
  dist_calc2 = cos(flat1);
  dist_calc2*=cos(flat2);
  dist_calc2*=sin(diflon/2.0);
  dist_calc2*=sin(diflon/2.0);
  dist_calc +=dist_calc2;

  dist_calc=(2*atan2(sqrt(dist_calc),sqrt(1.0-dist_calc)));
  
  dist_calc*=6371000.0; //Converting to meters

  return dist_calc;
}