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Fri Jun 30 05:58:03 2006 UTC (19 years ago) by edhill
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add initial description of SPGrid

1 edhill 1.1 % $Header: $
2     % $Name: $
3    
4     \section{Grid Generation}
5     \label{sec:pkg:grid_gen}
6     \begin{rawhtml}
7     <!-- CMIREDIR:package_grid_gen: -->
8     \end{rawhtml}
9    
10    
11     The horizontal discretizations within MITgcm have been written to work
12     with many different grid types including:
13     \begin{itemize}
14     \item cartesian coordinates
15     \item spherical polar (``latitude-longitude'') coordinates
16     \item general curvilinear orthogonal coordinates
17     \end{itemize}
18     The last of these, especially when combined with the domain
19     decomposition capabilities of MITgcm, allows a great degree of grid
20     flexibility. To date, general curvilinear orthogonal coordinates have
21     been used primarily (in fact, almost exclusively) in conjunction with
22     so-called ``cube-sphere'' grids. However, it is important to observe
23     that cube-sphere arrangements are only one example of what is possible
24     with domain-decomposed logically rectangular tiles each containing
25     curvilinear orthogonal coordinate systems. Much more sophisticated
26     domains can be imagined and constructed.
27    
28     In order to explore the possibilities of domain-decomposed curvilinear
29     orthogonal coordinate systems, a suite of grid generation software
30     called ``SPGrid'' (for SPherical Gridding) has developed. SPGrid is a
31     relatively new facility and papers detailing its algorithms are in
32     preparation. Althogh SPGrid is new and still rapidly developing, it
33     has already demonstrated the ability to generate some useful and
34     interesting grids.
35    
36     This section provides a very brief introduction to SPGrid and shows
37     some early results. For further information, please contact the
38     MITgcm support list:
39     \begin{center}
40     \begin{rawhtml} <A href="mailto:MITgcm-support@mitgcm.org"> \end{rawhtml}
41     MITgcm-support@mitgcm.org
42     \begin{rawhtml} </A> \end{rawhtml}
43     \end{center}
44    
45    
46     \subsection{Using SPGrid}
47    
48     The SPGrid software is not a single program. Rather, it is a
49     collection of \CC code and MatLAB scripts that can be used as a
50     framework or library for grid generation. Currently, grid creation is
51     accomplished by writing a \CC ``driver'' program that specifies the
52     shape and connectivity of tiles and the preferred grid sizes (in the
53     sense of the number of grid cells) and edge locations of the cells at
54     the edges of grid faces. The driver program then passes this
55     information to the SPGrid library which generates the actual grid and
56     produces the output files that describe it.
57    
58     Currently, driver programs are available for a few examples including
59     cubes, ``lat-lon caps'' (cube topologies that have conformal caps at
60     the poles and are exactly lat-lon channels for the remainder of the
61     domain), and some simple ``embedded'' regions that are meant to be
62     used within typical cubes or traditional lat-lon grids.
63    
64     To create new grids, one may start with an existing driver program and
65     modify it to describe a domain that has a different arrangement. The
66     number, location, size, and connectivity of grid ``faces'' (the name
67     used for the logically rectangular regions) can be readily changed.
68     Further, the number of grid cells within faces and the location of
69     the grid cells at the face edges can also be specified.
70    
71    
72     \subsubsection{SPGrid Requirements}
73    
74     The following programs and libraries are required to build and/or run
75     the SPGrid suite:
76     \begin{itemize}
77     \item MatLAB is a run-time requirement since many of the generation
78     algorithms have been written as MatLAB scripts: \\
79     \begin{rawhtml} <A href="http://www.mathworks.com"> \end{rawhtml}
80     \texttt{http://www.mathworks.com}
81     \begin{rawhtml} </A> \end{rawhtml}
82    
83     \item the Wild Magic graphics engine (a \CC library) is needed for the
84     main ``driver'' code: \\
85     \begin{rawhtml} <A href="http://geometrictools.com/"> \end{rawhtml}
86     \texttt{http://geometrictools.com/}
87     \begin{rawhtml} </A> \end{rawhtml}
88    
89     \item the NetCDF library is needed for file I/O: \\
90     \begin{rawhtml} <A href="http://www.mathworks.com"> \end{rawhtml}
91     \texttt{http://www.mathworks.com}
92     \begin{rawhtml} </A> \end{rawhtml}
93    
94     \item the BOOST Serialization library is used for I/O: \\
95     \begin{rawhtml} <A href="http://www.boost.org"> \end{rawhtml}
96     \texttt{http://www.boost.org}
97     \begin{rawhtml} </A> \end{rawhtml}
98    
99     \item a typical Unix/Linux build environment including the make
100     utility (preferably Gnu Make) and a \CC compiler (SPGrid was
101     developed with g++ v3.x and v4.x).
102     \end{itemize}
103    
104    
105     \subsubsection{Obtaining SPGrid}
106    
107     The latest version can be obtained from:
108     \begin{center}
109     \begin{rawhtml} <A href="http://mitgcm.org/eh3/grids/spgrid_releases/>
110     \end{rawhtml}
111     \texttt{http://mitgcm.org/eh3/grids/spgrid\_releases/}
112     \begin{rawhtml} </A> \end{rawhtml}
113     \end{center}
114    
115    
116     \subsubsection{Building SPGrid}
117    
118     The procedure for building is similar to many open source projects:
119     \begin{verbatim}
120     tar -xf spgrid-0.9.4.tar.gz
121     cd spgrid-0.9.4
122     export CPPFLAGS="-I/usr/include/netcdf-3"
123     export LDFLAGS="-L/usr/lib/netcdf-3"
124     ./configure
125     make
126     \end{verbatim}
127     where the \texttt{CPPFLAGS} and\texttt{LDFLAGS} environment variables
128     can be edited to reflect the locations of all the necessary
129     dependencies. SPGrid is known to work on Fedora Core Linux and is
130     likely to work on most any Linux distribution that provides the needed
131     dependencies.
132    
133    
134     \subsubsection{Using SPGrid}
135    
136     Within the \texttt{src} sub-directory, various example programs
137     exist. These example programs describe small but complete domains and
138     can generate the input (formatted as either binary ``mitgrid'' or
139     netCDF) files required by MITgcm.
140    
141     One such example is called ``SpF\_test\_cube\_cap'' and it can be run
142     with the following sequence of commands:
143     \begin{verbatim}
144     cd spgrid-0.9.4/src
145     mkdir SpF_test_cube_cap.d
146     ( cd SpF_test_cube_cap.d && ln -s ../../scripts/*.m . )
147     ./SpF_test_cube_cap
148     \end{verbatim}
149     which should create a series of output files of the form
150     \begin{verbatim}
151     SpF_test_cube_cap.d/grid_*.mitgrid
152     SpF_test_cube_cap.d/grid_*.nc
153     SpF_test_cube_cap.d/std_topology.nc
154     \end{verbatim}
155     which describe each face of the domain and how the faces are
156     connected.
157    
158    
159     \subsection{Example Grids}
160    
161     The following grids are various examples created with SPGrid.

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