Output grids

SWAN can provide output on uniform, rectilinear spatial grids that are independent from the input grids and from the computational grid. In the computation with a curvilinear computational grid, curvilinear output grids are available in SWAN. This also holds for triangular meshes. An output grid has to be specified by the user with an arbitrary resolution, but it is of course wise to choose a resolution that is fine enough to show relevant spatial details. It must be pointed out that the information on an output grid is obtained from the computational grid by bi-linear interpolation (output always at computational time level). This implies that some inaccuracies are introduced by this interpolation. It also implies that bottom or current information on an output plot has been obtained by interpolating twice: once from the input grid to the computational grid and once from the computational grid to the output grid. If the input-, computational- and output grids are identical, then no interpolation errors occur.


In the regions where the output grid does not cover the computational grid, SWAN assumes output values equal to the corresponding exception value. For example, the default exception value for the significant wave height is $-$9. The exception values of output quantities can be changed by means of the QUANTITY command.


In nonstationary computations, output can be requested at regular intervals starting at a given time always at computational times.