code: def bottom(self, z=0, radius=0, degrees=0, reference=None):
          
          coordinates = self.from_center(
              r=radius,
              theta=(degrees / 180) * math.pi,
              h=-1,
              reference=reference)
          return (self, coordinates + (0, 0, z))
docs: Returns (:Placeable, :Vector:) tuple where :Vector:
          corresponds to the bottom of a :Placeable:
  
          If :reference: :Placeable: is provided, returns
          the :Vector: within :reference: coordinate system