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### Grid and bathymetry

The grid for this example was generated with GAMBIT and is shown in Figure 3 (for tips on using GAMBIT for SUNTANS please see
`http://suntans.stanford.edu/documentation/suntans_tutorial.pdf`). Grids like this can be generated by obtaining a coastline from the NOAA coastline extractor
`http://rimmer.ngdc.noaa.gov/coast/`
and reading it into a grid generation program after converting the coordinates to a Cartesian grid. Most grids in SUNTANS are obtained with a UTM projection, but for larger grids that cross over multiple UTM zones, the Mercator projection is also suitable. Upon running SUNTANS (with `-g -vv`), Voronoi distance statistics will be output as follows:

```Voronoi statistics:
Minimum distance: 1.97e+02
Maximum distance: 4.43e+03
Mean distance: 2.85e+03
Standard deviation: 4.14e+02
```
Note that while the minimum distance in this example is acceptable, the Voronoi distances do not indicate whether there are degenerate cells in the domain (i.e. obtuse triangles). In order to correct for any degenerate triangles, the parameter `CorrectVoronoi` is set to `-1`, and the parameter `VoronoiRatio` is set to `85` degrees (these parameters are in `suntans.dat`). This corrects any triangles with angles greater than 85 degrees by placing the Voronoi points at the triangle centroids. After correction, the statistics are displayed as
```Corrected 11 of 1534 cells with angles > 85.0 degrees (0.72%).
Voronoi statistics after correction:
Minimum distance: 9.49e+02
Maximum distance: 4.34e+03
Mean distance: 2.85e+03
Standard deviation: 3.95e+02
```
This highlights the fact that 11 cells in the grid were obtuse and were corrected. Also note that as a result of the correction the minimum distance between Voronoi points increased from 197 m to 949 m. This substantially raises the minimum allowable time step for stability of the nonlinear advection terms.
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For the bathymetry, 250 m resolution bathymetry is available in the file
`rundata/mbay_bathy.dat` which was obtained from the MBARI multibeam survey
`http://www.mbari.org/data/mapping/monterey/default.htm`
This file is specified by the `depth` variable in `suntans.dat`. The interpolated bathymetry is depicted in Figure 4. Upon running SUNTANS, bathymetry from this file is interpolated onto the (possibly corrected) Voronoi points. Because this procedure can take quite some time, it is a good idea to only run it when necessary and use the pre-interpolated bathymetry for subsequent runs. Each time SUNTANS interpolates bathymetry, it outputs the interpolated bathymetry into the file `mbay_bathy.dat-voro` (it appends ``-voro'' to the specified bathymetry file). This file is created when the variable `IntDepth` is set to 1 in `suntans.dat`. Otherwise, if this variable is set to 2, data is not interpolated but instead is read in from the `-voro` file. Note that any time changes are made to the Voronoi points, the bathymetry should be re-interpolated.

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Next: Initial conditions Up: Tidal forcing Previous: Tidal forcing   Contents
2014-08-06