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:

1:	equi-distant plane grid - $dx$, $dy$ are constant - but not necessarily equal
2:	equi-distant spherical grid - $dlon$, $dlat$ are constant - and again not necessarily equal
3:	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:

1:	proper monotone coordinate informtion in the xy-plane with equidistant spacing. The name of the coordinate variables are $xcord$ and $ycord$.
2:	proper monotone coordinate informtion on the sphere with equidistant spacing in longitude and latitude. The names of the coordinate variables are $xcord$ and $ycord$.
3:	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:

A:	$latu$ 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 $latv$.
B:	$lonc$, $latc$ 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.