@classmethod
def HomogeneousWalthall(cls, param1, param2, param3, albedo):
    """Parameterisation for a surface BRDF based on the Walthall et al. model.

        The parameters are:

        - term in square ts*tv
        - term in square ts*ts+tv*tv
        - term in ts*tv*cos(phi) (limacon de pascal)
        - albedo

        """
    return (
        """0 Homogeneous surface
1 (directional effects)
4 (Walthall et al. model)
%f %f %f %f
"""
         % (param1, param2, param3, albedo))
