code: func (t T) HaversineDistance(c1, c2 kml.Coordinate) float64 {
  	lat1 := c1.Lat * radians
  	lat2 := c2.Lat * radians
  	deltaLat := lat2 - lat1
  	deltaLon := (c1.Lon - c2.Lon) * radians
  	a := math.Sin(deltaLat/2)*math.Sin(deltaLat/2) + math.Cos(lat1)*math.Cos(lat2)*math.Sin(deltaLon/2)*math.Sin(deltaLon/2)
  	c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
  	return t.R * c
  }
docs: // HaversineDistance returns the great circle distance beween c1 and c2 using
  // the Haversine formula. Altitude is ignored.