/[MITgcm]/MITgcm_contrib/netcdf_matlab_examples/README.txt
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Contents of /MITgcm_contrib/netcdf_matlab_examples/README.txt

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Sat Jan 3 19:46:51 2004 UTC (14 years, 11 months ago) by edhill
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 o notes about Ingrid's "X", "Y" variable naming oddities
 o add the latlon_2d example of non-lat-lon-aligned grids
 o add simple worldbath example

1
2 Examples: NetCDF & MatLAB
3 ==========================
4
5 These directories contain examples of MatLAB commands for reading,
6 creating, and modifying NetCDF files. All the scripts use Chuck
7 Denham's MatLAB package which can be obtained at:
8
9 "MexCDF and NetCDF Toolbox For Matlab-5&6"
10 http://woodshole.er.usgs.gov/staffpages/cdenham/public_html/MexCDF/nc4ml5.html
11
12 and must first be installed.
13
14
15 The NetCDF files generated here are intended for use with Ingrid:
16
17 http://ingrid.mit.edu/
18
19 As a result, they approximately follow the simple COARDS convention
20 which is described at:
21
22 http://www.unidata.ucar.edu/packages/netcdf/conventions.html
23 http://ferret.wrc.noaa.gov/noaa_coop/coop_cdf_profile.html
24
25
26 The key items for the use of NetCDF files within Ingrid are:
27
28 1) Although coordinate names such as "lat", "lon", "latitude",
29 etc. will work without any problems for plotting data, it seems
30 that the names "X" and "Y" sould be preferred for the coordinate
31 names so that calculations (eg. curl) can be applied to those
32 data sets. For an example see:
33
34 TRENBERTH_tau_mask/EH3_notes_mask.txt
35
36 where both naming styles are used but the latter "X", "Y" naming
37 scheme should be preferred.
38
39 2) In order to work with the Ingrid "plot land" option, dimensions
40 should have units of "degree_east" and "degree_north" as, for
41 example, specified by:
42
43 nc{'X'}.units = 'degree_east';
44 nc{'Y'}.units = 'degree_north';
45
46 The actual dimension names (eg. "lat" or "Y") are unimportant.
47
48 3) It is generally a good idea to set the "gridtype" to 1 or 0 to
49 indicate that the coordinate "wraps" or not. The gridtype
50 attribute allows Ingrid to, for instance, plot longitudinal data
51 over "wrapped" ranges such as -100 to 500deg. The attribute can
52 be set using commands such as:
53
54 nc{'X'}.gridtype = ncint(1);
55 nc{'Y'}.gridtype = ncint(0);
56
57 4) Ingrid does seem to correctly handle the "_FillValue" attribute
58 and it can be set using a MatLAB command such as:
59
60 nc{ idu }.FillValue_ = ncdouble(-9999.0);
61
62 [ Note how the "_" character is moved to the end of the attribute
63 name since MatLAB cannot correctly handle variable names with a
64 leading underscore. ]

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