MATLAB NETCDF Quickstart

This document explains how to open and read a NETCDF file from MATLAB. Please note that MATLAB r2008 or later comes pre-built with NETCDF support.

Please check http://www.mathworks.com/access/helpdesk/help/techdoc/ref/f16-6011seg02.... or just google "netcdf matlab site:mathworks.com"

First, get a NETCDF file

[anand@leo ~]$ ls -lh atm.nc
-rw-r--r-- 1 anand anand 63M Feb 24 11:08 atm.nc
[anand@leo ~]$

Use a command on the linux prompt and check the structure and variables in the file:

[anand@leo ~]$ ncdump -h atm.nc
netcdf atm {
dimensions:
        lon = 198 ;
        lat = 93 ;
        level = 18 ;
        time = UNLIMITED ; // (4 currently)
variables:
        float lon(lon) ;
                lon:long_name = "Longitude" ;
                lon:units = "degrees_east" ;
                lon:actual_range = 88.5609f, 141.7089f ;
        float lat(lat) ;
                lat:long_name = "Latitude" ;
                lat:units = "degrees_north" ;
                lat:actual_range = -12.18246f, 12.44604f ;
        float level(level) ;
                level:long_name = "Height_Index" ;
                level:units = "level" ;
                level:actual_range = 1050.f, 0.f ;
        double time(time) ;
                time:long_name = "Time" ;
                time:units = "hours since 1900-1-1 00:00:0.0" ;
                time:actual_range = 885696., 885714. ;
        float U(time, level, lat, lon) ;
                U:long_name = "Zonal Wind" ;
                U:units = "m/s" ;
                U:missing_value = -1.e+30f ;
        float V(time, level, lat, lon) ;
                V:long_name = "Meridional Wind" ;
                V:units = "m/s" ;
                V:missing_value = -1.e+30f ;
        float OMEGA(time, level, lat, lon) ;
                OMEGA:long_name = "Omega" ;
                OMEGA:units = "hPa" ;
                OMEGA:missing_value = -1.e+30f ;
        float TK(time, level, lat, lon) ;
                TK:long_name = "Temperature" ;
                TK:units = "K" ;
                TK:missing_value = -1.e+30f ;
        float QD(time, level, lat, lon) ;
                QD:long_name = "Mixing Ratio" ;
                QD:units = "kg/kg" ;
                QD:missing_value = -1.e+30f ;
        float QC(time, level, lat, lon) ;
                QC:long_name = "Cloud Mixing Ratio" ;
                QC:units = "kg/kg" ;
                QC:missing_value = -1.e+30f ;
        float RH(time, level, lat, lon) ;
                RH:long_name = "Relative Humidity" ;
                RH:units = "fraction" ;
                RH:missing_value = -1.e+30f ;
        float HGT(time, level, lat, lon) ;
                HGT:long_name = "Geopotential Height" ;
                HGT:units = "m" ;
                HGT:missing_value = -1.e+30f ;
        float TH(time, level, lat, lon) ;
                TH:long_name = "Potential Temperatur" ;
                TH:units = "K" ;
                TH:missing_value = -1.e+30f ;
        float TD(time, level, lat, lon) ;
                TD:long_name = "Dew Point Temperatur" ;
                TD:units = "K" ;
                TD:missing_value = -1.e+30f ;
        float VOR(time, level, lat, lon) ;
                VOR:long_name = "Vorticity (Horizonta" ;
                VOR:units = "m/s" ;
                VOR:missing_value = -1.e+30f ;
        float DIV(time, level, lat, lon) ;
                DIV:long_name = ;
                DIV:units = "m/s" ;
                DIV:missing_value = -1.e+30f ;
        float PS(time, lat, lon) ;
                PS:long_name = "Surface Pressure" ;
                PS:units = "hPa" ;
                PS:missing_value = -1.e+30f ;
        float RT(time, lat, lon) ;
                RT:long_name = "Total Precip" ;
                RT:units = "mm/day" ;
                RT:missing_value = -1.e+30f ;
        float TGRND(time, lat, lon) ;
                TGRND:long_name = "Ground Temperature" ;
                TGRND:units = "K" ;
                TGRND:missing_value = -1.e+30f ;
        float SMT(time, lat, lon) ;
                SMT:long_name = "Total Soil Water" ;
                SMT:units = "mm" ;
                SMT:missing_value = -1.e+30f ;
        float RB(time, lat, lon) ;
                RB:long_name = "Base Flow" ;
                RB:units = "mm/day" ;
                RB:missing_value = -1.e+30f ;
        float SLP(time, lat, lon) ;
                SLP:long_name = "Sea Level Temperatur" ;
                SLP:units = "hPa" ;
                SLP:missing_value = -1.e+30f ;

// global attributes:
                :domxmin = 88.5609f ;
                :domxmax = 141.7089f ;
                :domymin = -12.18246f ;
                :domymax = 12.44604f ;
                :domzmin = 1050.f ;
                :domzmax = 0.f ;
}

Start MATLAB:

[anand@leo ~]$ matlab -nodisplay -nojvm

                                                          < M A T L A B (R) >
                                                Copyright 1984-2009 The MathWorks, Inc.
                                              Version 7.8.0.347 (R2009a) 64-bit (glnxa64)
                                                           February 12, 2009

To get started, type one of these: helpwin, helpdesk, or demo.
For product information, visit www.mathworks.com.

Open the NETCDF File:

>> ncid=netcdf.open('atm.nc','NOWRITE')

ncid =

Try some queries:

>> [ndims,nvars,ngatts,unlimdimid] = netcdf.inq(ncid)

ndims =

nvars =

ngatts =

unlimdimid =

Get the name of the first variable.

>> [varname, xtype, varDimIDs, varAtts] = netcdf.inqVar(ncid,0);
>> varname
varname =
lon
>> xtype
xtype =
     5
>> varDimIDs
varDimIDs =
     0
>> varAtts
varAtts =
     3

Get variable ID of the first variable, given its name.

>> varid = netcdf.inqVarID(ncid,varname);
>> varid
varid =
0

Get the value of the first variable, given its ID.

>> data = netcdf.getVar(ncid,varid)
data =
   88.5609
   88.8307
   89.1005
   89.3703
   89.6400
   89.9098
   90.1796

Also try:

>> varid = netcdf.inqVarID(ncid,'lat');
>> data = netcdf.getVar(ncid,varid);
>> data

data =

-12.1825