Introduction to the calculation domain

This module handles all tasks related to the definition of the computational domain - except reading in variables from file. The required information depends on the $ grid\_type$ and also on the complexity of the model simulation to be done.
The mandatory varible $ grid\_type$ read from the file containing the bathymetry and coordinate information (presently only NetCDF is supported) is guiding subsequent tasks. $ grid\_type$ can take the following values:

equi-distant plane grid - $ dx$, $ dy$ are constant - but not necessarily equal
equi-distant spherical grid - $ dlon$, $ dlat$ are constant - and again not necessarily equal
curvilinear grid in the plane - $ dx$, $ dy$ are both functions of (i,j). The grid must be orthogonal

For all values of $ grid\_type$ the bathymetry given on the T-points (see the GETM manual for definition) must be given.

Based on the value of $ grid\_type$ the following additional variables are required:

proper monotone coordinate informtion in the xy-plane with equidistant spacing. The name of the coordinate variables are $ xcord$ and $ ycord$.
proper monotone coordinate informtion on the sphere with equidistant spacing in longitude and latitude. The names of the coordinate variables are $ xcord$ and $ ycord$.
position in the plane of the grid-vertices. These are called X-points in GETM. The names of these two variables are $ xx$ and $ yx$.

In addition to the above required grid information the following information is necessary for specific model configurations:

$ latu$ and $ latv$
If $ f\_plane$ is false information about the latitude of U- and V-points are required for calculating the Coriolis term correctly. For $ grid\_type=1$ $ latu$ and $ latv$ are calculated based on an additional field $ latc$ i.e. the latitude of the T-points. For $ grid\_type=3$ $ latx$ i.e. the latitude of the X-points will have to be provided in order to calculate $ latu$ and $ latv$.
$ lonc$, $ latc$ and $ convc$
The longitude, latitude positions of the T-points are required when using forcing from a NWP-model. $ lonc$ and $ latc$ are used to do spatial interpolation from the meteo-grid to the GETM model and $ convc$ is the rotation of the local grid from true north.

In addition to the information above a few files are optionally read in $ init\_domain()$. Information about open boundaries, modifications to the bathymetry and the calculation masks are are done via simple ASCII files.

kklingbe 2017-10-02