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1\newpage
2\appendix
3\chapter{The grid types for the transformations}
4\label{subsec_gridtypes}
5
6As described in section \ref{sec_transformations}, the different
7transformations in OASIS3 support different types of grids. The
8characteristics of these grids are detailed here.
9
10\begin{enumerate}
11
12\item Grids supported for the {\tt INTERP}
13    interpolations (see section \ref{subsec_interp})
14
15\begin{itemize}
16 
17\item {\tt `A' grid}: this is a regular Lat-Lon grid covering either
18      the whole globe or an hemisphere, going from South to North and
19      from West to East.  There is no grid point at the
20      pole and at the equator, and the first latitude has an offset of
21      0.5 grid interval. The first longitude is 0$^o$ (the Greenwhich
22      meridian) and is not repeated at the end of the grid ({\tt
23      \$CPER} = P and {\tt \$NPER}= 0).  The latitudinal grid length
24      is 180/NJ for a global grid, 90/NJ otherwise. The longitudinal
25      grid length is 360/NI.
26
27\item {\tt `B' grid}: this is a regular Lat-Lon grid covering either
28      an hemisphere or the whole globe, going from South to North and
29      from West to East. There is a grid point at the
30      pole and at the equator (if the grid is hemispheric or global
31      with NJ odd). The first longitude is 0$^o$ (the Greenwhich
32      meridian), and is repeated at the end of the grid ({\tt \$CPER}
33      = P and {\tt \$NPER}= 1).  The latitudinal grid length is
34      180/(NJ-1) for a global grid, 90/(NJ-1) otherwise. The
35      longitudinal grid length is 360/(NI-1).
36
37 
38\item {\tt `G' grid}: this is a irregular Lat-Lon Gaussian grid
39covering either an hemisphere or the whole globe, going from South to
40North and from West to East. This grid is used in spectral models. It
41is very much alike the A grid, except that the latitudes are not
42equidistant. There is no grid point at the pole and at the
43equator. The first longitude is 0$^o$ (the Greenwhich meridian) and is
44not repeated at the end of the grid ({\tt \$CPER} = P and {\tt
45\$NPER}= 0).  The longitudinal grid length is 360/NI. 
46
47
48\item {\tt `L' grid}: this type covers regular Lat-Lon grids in
49      general, going from South to
50North and from West to East.. The grid can be described by the latitude and the
51      longitude of the southwest corner of the grid, and by the
52      latitudinal and longitudinal grid mesh sizes in degrees.
53
54\item {\tt `Z' grid}: this is a Lat-Lon grid with non-constant
55      latitudinal and longitudinal grid mesh sizes, going from South to
56North and from West to East. The deformation of
57      the mesh can be described with the help of 1-dimensional
58      positional records in each direction. This grid is periodical
59      ({\tt \$CPER} = P) with {\tt \$NPER} overlapping grid points.
60
61\item {\tt `Y' grid}: this grid is like `Z' grid except that it is
62      regional ({\tt \$CPER} = R and {\tt \$NPER} = 0).
63 
64 \end{itemize}
65
66\item Grids supported for the {\tt SCRIPR} interpolations
67
68\begin{itemize}
69
70\item {\tt `LR' grid}: The longitudes and the latitudes of
71  2D Logically-Rectangular (LR) grid points can be described by two arrays
72  {\tt longitude(i,j)} and {\tt latitude(i,j)}, where i and j
73  are respectively the first and second index dimensions. Streched
74  or/and rotated grids are LR grids. Note that A, B, G, L, Y, or Z
75  grids are all particular cases of LR grids.
76
77\item {\tt `U' grid}: Unstructured (U) grids do have any particular
78      structure. The longitudes and the latitudes of 2D Unstructured
79      grid points must be described by two arrays {\tt
80      longitude(nbr\_pts,1)} and {\tt latitude(nbr\_pts,1)}, where nbr\_pts
81      is the total grid size.
82
83\item {\tt `D' grid} The Reduced (D) grid is composed of a certain
84number of latitude circles, each one being divided into a varying
85number of longitudinal segments. In OASIS3, the grid data (longitudes,
86latitudes, etc.) must be described by arrays dimensioned {\tt
87(nbr\_pts,1)}, where {\tt nbr\_pts} is the total number of grid
88points. There is no overlap of the grid, and no grid point at the
89equator nor at the poles. There are grid points on the Greenwich
90meridian.
91 
92\end{itemize}
93
94\end{enumerate}
95
96
97
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