Two types of discretisation are available; 360 degree rose and directional sector. The 360 degrees compass rose is typically chosen for varying wind/wave/swell directions. However, if the expected wind/wave/swell directions fall within a predefined range of directions, the choice of a directional sector type of discretisation is recommended as it reduce the computational time.
The number of discrete directions should be large enough to resolve the directional variation of the waves. For swell with a relative narrow directional distribution of the wave action/energy a relatively small directional resolution is needed, Dq < 2°-10° (the first number (2°) corresponds to coastal areas and the last number (10°) to offshore areas. For wind waves with a wider directional distribution of the action/energy a resolution of about Dq < 10°-30° is usually sufficient.