Several types of grids and time window(s) need to be defined: (a) spectral grid, (b) spatial (geographic)
grids and time window(s) in case of nonstationary computations.

The **spectral** grid that need to be defined by the user is a __computational__ spectral grid on
which SWAN performs the computations.

SWAN has the option to make computations that can be nested in (coarse) SWAN, WAM or WAVEWATCH
III. In such cases, the spectral grid need not be equal to the spectral grid in the coarse SWAN, WAM or
WAVEWATCH III run.

The **spatial** grids that need to be defined by the user are (if required):

- a
__computational__spatial grid on which SWAN performs the computations, - one (or more) spatial
__input__grid(s) for the bottom, current field, water level, bottom friction and wind (each input grid may differ from the others) and - one (or more) spatial
__output__grid(s) on which the user requires output of SWAN.

For one-dimensional situations, i.e. /

If a uniform, rectangular computational spatial grid is chosen in SWAN, then all input and output grids must be uniform and rectangular too, but they may all be different from each other.

If a curvilinear computational spatial grid is chosen in SWAN, then

If an unstructured computational spatial grid is chosen in SWAN, then

SWAN has the option to make computations that are nested in (coarse) SWAN, WAM or WAVEWATCH III. In such runs, SWAN interpolates the spatial boundary of the SWAN, WAM or WAVEWATCH III grid to the (user provided) grid of SWAN (that needs to (nearly) coincide along the grid lines of WAM or WAVEWATCH III or the output nest grid boundaries of SWAN). Since, the computational grids of WAM and WAVEWATCH III are in spherical coordinates, it is recommended to use spherical coordinates in a nested SWAN when nesting in WAM or WAVEWATCH III.

SWAN using an

Nesting from a 2D model to a 1D model is possible although is should not be done by using the commands

Similarly, the wind fields may be available in different

- one
__computational time window__in which SWAN performs the computations, - one (or more)
__input time window(s)__in which the bottom, current field, water level, bottom friction and wind field (if present) are given by the user (each input window may differ form the others) and - one (or more)
__output time window(s)__in which the user requires output of SWAN.

During the computation SWAN obtains bottom, current, water level, wind and bottom friction information by tri-linear