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Examples: NetCDF & MatLAB |
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========================== |
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These directories contain examples of MatLAB commands for reading, |
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creating, and modifying NetCDF files. All the scripts use Chuck |
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Denham's MatLAB package which can be obtained at: |
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"MexCDF and NetCDF Toolbox For Matlab-5&6" |
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http://woodshole.er.usgs.gov/staffpages/cdenham/public_html/MexCDF/nc4ml5.html |
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and must first be installed. |
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The NetCDF files generated here are intended for use with Ingrid: |
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http://ingrid.mit.edu/ |
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As a result, they approximately follow the simple COARDS convention |
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which is described at: |
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http://www.unidata.ucar.edu/packages/netcdf/conventions.html |
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http://ferret.wrc.noaa.gov/noaa_coop/coop_cdf_profile.html |
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The key items for the use of NetCDF files within Ingrid are: |
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1) Although coordinate names such as "lat", "lon", "latitude", |
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etc. will work without any problems for plotting data, it seems |
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that the names "X" and "Y" sould be preferred for the coordinate |
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names so that calculations (eg. curl) can be applied to those |
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data sets. For an example see: |
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TRENBERTH_tau_mask/EH3_notes_mask.txt |
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where both naming styles are used but the latter "X", "Y" naming |
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scheme should be preferred. |
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2) In order to work with the Ingrid "plot land" option, dimensions |
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should have units of "degree_east" and "degree_north" as, for |
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example, specified by: |
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nc{'X'}.units = 'degree_east'; |
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nc{'Y'}.units = 'degree_north'; |
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The actual dimension names (eg. "lat" or "Y") are unimportant. |
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3) It is generally a good idea to set the "gridtype" to 1 or 0 to |
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indicate that the coordinate "wraps" or not. The gridtype |
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attribute allows Ingrid to, for instance, plot longitudinal data |
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over "wrapped" ranges such as -100 to 500deg. The attribute can |
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be set using commands such as: |
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nc{'X'}.gridtype = ncint(1); |
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nc{'Y'}.gridtype = ncint(0); |
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4) Ingrid does seem to correctly handle the "_FillValue" attribute |
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and it can be set using a MatLAB command such as: |
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nc{ idu }.FillValue_ = ncdouble(-9999.0); |
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[ Note how the "_" character is moved to the end of the attribute |
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name since MatLAB cannot correctly handle variable names with a |
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leading underscore. ] |