Error in creating netCDF for GrADS reading

[Owen Doherty]

Dear Jennifer et al,

Thanks for your help.  Here is the information you requested.

1) ncdump output (omitting the data section for space constraints, but 
that looks good)
owen at graupel:~/data/barbados$ ncdump -c test_ncgen6.nc
netcdf test_ncgen6 {
dimensions:
        longitude = 144 ;
        latitude = 73 ;
        t = 31 ;
        z = 9 ;
variables:
        double longitude(longitude) ;
                longitude:units = "degrees_east" ;
        double latitude(latitude) ;
                latitude:units = "degrees_north" ;
        double t(t) ;
                t:units = "seconds since 1970-1-1 00:00:00" ;
        double z(z) ;
                z:units = "lev" ;
                z:valid_range = 200., 1000. ;
        float omejjam(longitude, latitude, t, z) ;
data:

2) Control files first for XDF and then for CTL

DSET ^test_ncgen6.nc
DTYPE netcdf
TITLE This is a test
UNDEF -9999
XDEF longitude 144 LINEAR 0.0 2.5
YDEF latitude 73 LINEAR -90.0 2.5
TDEF t 31 LINEAR 0Z01JUN1979 1YR
ZDEF z  9 LEVELS 1000 925 850 700 600 500 400 300 250
VARS 1
omejjam=>ome 9 99 longitude,latitude,t,z  seasonal mean vertical motion
ENDVARS

DSET ^test_ncgen6.nc
DTYPE netcdf
TITLE This is a test
OPTIONS little_endian
UNDEF -9999
XDEF 144 LINEAR 0.0 2.5
YDEF 73 LINEAR -90.0 2.5
TDEF 31 LINEAR 0Z01JUN1979 1YR
ZDEF 9 LEVELS 1000 925 850 700 600 500 400 300 250
VARS 1
omejjam=>ome 9 x,y,z,t seasonal mean vertical motion
ENDVARS

3) Version of Grads: Version 2.0.a5.oga.5

4) Error message received:
No error exactly, but rather all the data is displayed as 0 to 9e+36 
interval 1e+36 instead of the actual values.

Thanks again,

Owen

Jennifer Adams wrote:
> Hi, Owen --
> It sounds like you have a problem specifying the undef value in your 
> data file. I can't help with the Matlab bit, but if you need help to 
> figure out why GrADS can't read your file, you need to post: 
>
> 1. The output from ncdump -c on your file (in case Matlab changes the 
> metadata in some way)
> 2. Your descriptor file (if you are using 'open' with 'dtype netcdf' 
> or 'xdfopen'). 
> 3. The version of GrADS that you are using
> 4. The text from the GrADS session that illustrates the error.  
>
> Jennifer
>
>
> On Jan 4, 2010, at 6:31 PM, Owen Doherty wrote:
>
>> Dear Grads Users,
>>
>> I am having difficulties creating and writing to a netcdf file that 
>> can be read by GrADS.  The data is loaded into GrADS successfully, 
>> but when displayed looks similar to improperly written binary data 
>> (e.g. all data is in the range of 0 to 9e+36 interval 1e+36).  Below 
>> are the steps I take to create a 4-D gridded netCDF, write to the 
>> netCDF and finally to read the file into GrADS.
>>
>> First, I create an nc file using the ncgen utility.  I have tried 
>> creating netCDF files with the variable both as "float" and "double" 
>> neither of which is successful and the errors from which appear to be 
>> similar.  Below is my source code (.cdl file) for this step.
>>
>> netcdf test_ncgen{
>> dimensions:
>>   longitude=144;
>>   latitude =73;
>>   t=31;
>>   z=9;
>>
>> variables:
>>   double longitude(longitude);
>>          longitude:units = "degrees_east";
>>
>>   double latitude(latitude);
>>          latitude:units = "degrees_north";
>>     double t(t);
>>       t:units = "seconds since 1970-1-1 00:00:00";
>>         double z(z);
>>       z:units = "lev";
>>       z:valid_range = 200.,1000.;
>>
>>   float omejjam(longitude, latitude, t, z) ;
>>      
>> data:
>> omejjam = 0;
>>
>> Secondly, I write to the netCDF file using MATLAB.  The write step is 
>> fairly simple and I suspect that I am missing something in here to 
>> have it write out as binary.  I have tried outputting single 
>> precision (float) and double precision data from MATLAB both of which 
>> result in the same error.  I am using MATLAB 2008b to do the writing. 
>>  The write command is as follows:
>>
>> nc=netcdf.open('test_ncgen.nc','nc_write');
>> [varname, xtype, dimids, numatts] = netcdf.inqVar(nc,4)% 0 - omejjam
>> netcdf.putVar(nc,4,omejjam);
>>
>> Lastly, I read the data into GrADS.  I have tried using sdfopen, 
>> xdfopen and the regular open command.  Adding the OPTION 
>> little_endian to the control file does not solve the issue.  All of 
>> the data looks erroneous, but consistent in between each different 
>> open command.  If anyone has any advice as to how to solve this 
>> problem, I would be grateful for the insight.
>>
>> Owen
>>
>> -- 
>> Owen Doherty
>> School of Marine and Atmospheric Science
>> Institute for Terrestrial and Planetary Atmospheres
>> 103 Discovery Hall
>> Stony Brook University
>> Stony Brook, NY 11794
>> (631)-632-8682 (office)
>
> --
> Jennifer M. Adams
> IGES/COLA
> 4041 Powder Mill Road, Suite 302
> Calverton, MD 20705
> jma at cola.iges.org <mailto:jma at cola.iges.org>
>
>
>


-- 
Owen Doherty
School of Marine and Atmospheric Science
Institute for Terrestrial and Planetary Atmospheres
103 Discovery Hall
Stony Brook University
Stony Brook, NY 11794
(631)-632-8682 (office)