docs: def sort_points(self, points):
          """Take points (z,x,q) and sort by increasing z"""
          new_points = []
          z_lookup = {}
          for z, x, Q in points:
              z_lookup[z] = (z, x, Q)
  
          z_keys = z_lookup.keys()
          z_keys.sort()
  
          for key in z_keys:
              new_points.append(z_lookup[key])
  
          return new_points