code: public double distance3D(final Coordinate c) {
          final double dx = getX() - c.getX();
          final double dy = getY() - c.getY();
          final double dz = getZ() - c.getZ();
          return Math.sqrt(dx * dx + dy * dy + dz * dz);
      }
docs: Computes the 3-dimensional Euclidean distance to another location.
  
  @param c
  a coordinate
  @return the 3-dimensional Euclidean distance between the locations