code: def remove_observations_below_value(x, y, z, val=0):
      r
      x_ = x[z >= val]
      y_ = y[z >= val]
      z_ = z[z >= val]
  
      return x_, y_, z_
docs: r"""Remove all x, y, and z where z is less than val.
  
      Will not destroy original values.
  
      Parameters
      ----------
      x: array_like
          x coordinate.
      y: array_like
          y coordinate.
      z: array_like
          Observation value.
      val: float
          Value at which to threshold z.
  
      Returns
      -------
      x, y, z
          List of coordinate observation pairs without
          observation values less than val.