code: def antipode(lon, lat):
      
      x, y, z = sph2cart(lon, lat)
      return cart2sph(-x, -y, -z)
docs: Calculates the antipode (opposite point on the globe) of the given point or
      points. Input and output is expected to be in radians.
  
      Parameters
      ----------
      lon : number or sequence of numbers
          Longitude in radians
      lat : number or sequence of numbers
          Latitude in radians
  
      Returns
      -------
      lon, lat : arrays
          Sequences (regardless of whether or not the input was a single value or
          a sequence) of longitude and latitude in radians.