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Units and coordinate systems

SWASH expects all quantities that are given by the user to be expressed in S.I. units: m, kg, s and composites of these with accepted compounds, such as Newton (N) and Pascal (Pa). Consequently, the water level and water depth are in m, flow velocity in m/s, etc. For wind, (incident) wave and flow direction both the Cartesian and a nautical convention can be used (see below). Directions and spherical coordinates are in degrees (0) and not in radians.


SWASH operates either in a Cartesian coordinate system or in a spherical coordinate system, i.e. in a flat plane or on a spherical Earth. In the Cartesian system, all geographic locations and orientations in SWASH, e.g. for the bottom grid or for output points, are defined in one common Cartesian coordinate system with origin (0,0) by definition. This geographic origin may be chosen totally arbitrarily by the user. In the spherical system, all geographic locations and orientations in SWASH, e.g. for the bottom grid or for output points, are defined in geographic longitude and latitude. Both coordinate systems are designated in this manual as the problem coordinate system.


In the input and output of SWASH the direction of wind, (incident) wave and current are defined according to either

All other directions, such as orientation of grids, are according to the Cartesian convention!


For regular grids, i.e. uniform and rectangular, Figure 4.1 (in Section 4.5) shows how the locations of the various grids are determined with respect to the problem coordinates. All grid points of curvilinear grids are relative to the problem coordinate system.


next up previous index
Next: Choice of grids and Up: General description and instructions Previous: Internal scenarios, shortcomings and   Index
The SWASH team 2017-04-06