Extract wave watch III significant wave height data

[lzh...@mail.usf.edu]

Hi, Rich,

I download wave watch III significant height data "multi_1.at_4m.hs.201412.grb2'.  Then I used the following matlab code to extract longitude, latitude, time, and significant height data:

fname='multi_1.at_4m.hs.201412.grb2';
nc=ncgeodataset(fname);
%  using nc.variables to check the variable names in this grb2 file.

lon=nc{'lon'}(:);
lat=nc{'lat'}(:);
ttt=nc{'time'}(:);
param='Significant_height_of_combined_wind_waves_and_swell_surface';
hss=nc{param}(:);

The longitude, latitude, and time can be correctly extracted, but significant wave height cannot and the following error message is shown:

Error using ncdataset/readdata (line 501)
Java exception occurred:
java.lang.OutOfMemoryError: Java heap space

Error in ncdataset/data (line 165)
                    d = obj.readdata(variable, first, last, stride);

Error in ncgeodataset/subsref (line 378)
                            B = builtin('subsref',obj,g);


Error in ncvariable/somedata (line 353)
                data = obj.dataset.data(name, first, last, stride);

Error in ncvariable/data (line 174)
                d = somedata(obj, 1, first, last, stride);

Error in ncgeovariable/subsref (line 1028)
                                        sref = obj.data(first, last, stride);


Error in ncgeodataset/subsref (line 408)
                        B = v.data(s(2).subs{:});

I know the array size of hss is 249x481x576.  I can use loop to extract them by using the following code:

for i=1:249
 hss(i,:,:)=squeeze(nc{param}(i,:,:));
end

but it is much slower. 

By the way, I can extract the first 100x481x576 by using hss=nc{param}(1:100,:,:);  Does this mean that the array size 249x481x576 exceeds the array defined in NCTOOLBOX?

Please advice;

Thanks,
Lianyuan

[Brian Schlining]

Hi Lianyuan,

You just need to increase the Java Heap size in Matlab. From the Matlab menu go to Preferences -> MATLAB -> General -> Java Heap Memory

More details can be found at http://blogs.mathworks.com/community/2010/04/26/controlling-the-java-heap-size/

Cheers

Brian

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[Rich Signell]

Don't try to load all time steps at once. Process each time step in a loop

nc{param}(istep,:,:)

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[eduardo sierra]

Hi all, this posts have been very helpful. I am also trying to download sig wave height using this code:

nc=ncgeodataset('multi_1.ak_10m.hs.201507.grb2');

nc.variables

>>ans = 

    'Significant_height_of_combined_wind_waves_and_swell_surface'

    'lat'

    'lon'

    'time'

Same as Lianyuan I can extract the longitude, latitude, and time, but significant wave height cannot be extracted and I get the following error message is shown:

ttt=nc{'time'}(:);

lat=nc{'lat'}(:);

lon=nc{'lon'}(:);

for i=1:249
 hss(i,:,:)=squeeze(nc{param}(i,:,:));
end

Undefined function or variable 'escapeName'.

Error in ncdataset/findvariable (line 447)

                v = obj.netcdf.findVariable(ucar.nc2.NetcdfFile.escapeName(variable))

Error in ncdataset/attributes (line 256)

                v = obj.findvariable(variable);

Error in ncgeodataset/geovariable (line 147)

                att = obj.attributes(variableName);

Error in ncgeodataset/subsref (line 410)

                    v = obj.geovariable(s(1).subs);

Do you have any suggestion?

Best Regards and thanks in advance!

Eduardo

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[Brian Schlining]

Hi Eduardo,

Can you post a file somewhere I can get it so I can duplicate the issue?

Thanks

Brian

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[eduardo sierra]

Thanks for responding Brian. I solved it. I was using the wrong name for the param variable.

Cheers to all contributors!

ES

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.~`` ' .          . `  . ` ` `   _ . -'     ' . . . Eduardo Sierra