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[netCDF #COH-743209]: problems reading NetCDF files using Matlab 2010a

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  • Subject: [netCDF #COH-743209]: problems reading NetCDF files using Matlab 2010a
  • Date: Mon, 15 Mar 2010 22:30:41 -0600
Hi Dr. Segal,

> I am trying to read NCEP reanalysis files (for example air.1987.nc )
> 
> I am using 64 bit Matlab on 64bit windows 7 machine.
> 
> The procedure I have wrote is:
> 
> ncid =
> netcdf.open('C:\Users\user\Documents\Wales\Regional\1987\air.1987.nc','NC_NOWRITE');
> [varname, xtype, varDimIDs, varAtts] = netcdf.inqVar(ncid,4);
> varid = netcdf.inqVarID(ncid,varname);
> air = netcdf.getVar(ncid,varid');
> 
> air is expected to contain temperatures in int16 variable, however when
> I check the values they don't come in K units, for example:
> >> air(1,1,1,1)
> 
> ans =
> 
> -24166
> 
> which is expected to be something about 250K.
> 
> It is important to note that other variables, for example:
> 
> [varname, xtype, varDimIDs, varAtts] = netcdf.inqVar(ncid,0);
> varid = netcdf.inqVarID(ncid,varname);
> level = netcdf.getVar(ncid,varid);
> 
> and here the data is accurate
> 
> level
> 
> level =
> 
> 1000
> 925
> 850
> 700
> 600
> 500
> 400
> 300
> 250
> 200
> 150
> 100
> 70
> 50
> 30
> 20
> 10

Does the "air" variable have the attributes "scale_factor" or "add_offset"?
If so, it would indicate that the data is packed, and should be unpacked
by applying the formula

  unpacked_data_value = packed_data_value * scale_factor + add_offset

If that doesn't explain the problem, try using the "ncdump" program to see
the values of the air variable.  If ncdump gets the right values but your Matlab
program doesn't, then that indicates a problem in your program or Matlab.  If
ncdump shows the wrong values, we might be able to determine the problem
by looking at the air.1987.nc file, if you could make it available.

--Russ

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: COH-743209
Department: Support netCDF
Priority: Normal
Status: Closed