That is you simply multiply the 2 D spectrum which already we have seen under random waves by a directional spread that is how the energy can be distributed. How the distribution of energy distribution of the energy in terms of direction can be described? So, that is obtained by D (f comma theta) which is directional distribution as a function of frequency and eta is that clear. So, now later we will see as we have seen here there are some standard spectra like Bretschneider spectrum, Jonswap spectrum, Pierson Moskowitz spectrum, Scott spectrum so many spectrums are there and we have also seen the usefulness of looking at presentation which can follow some kind of a standard distribution. In a similar way we also have some standard distribution for directional spread.