Re: Byte array

You are correct Dave. I skimmed the original message a bit too quickly. It is a mystery at this point why the _FillValue is set to 0 if that is supposed to mean that the data is good.
 -dave

On Jul 29, 2013, at 12:42 PM, Dave Allured - NOAA Affiliate <dave.allured@noaa.gov> wrote:

> Marston and Dave B,
>
> Marston originally said, "... in the CloudSat docs, the Data_quality
> flag is set to 0 if the data is good." If the _FillValue attribute is
> present and zero after NCL reads this hdf4-eos file, this is totally
> inconsistent with this documentation, and there is an error somewhere.
>
> Possibilities include a special case problem in the NCL driver, the
> hdf4-eos file was modified or produced under different rules, damaged
> file, mistake in the documentation, subtle problem in the user NCL
> script, etc.
>
> I think that Dave B's suggestion to delete the _FillValue attribute in
> NCL memory will mitigate the problem, but I would still wonder how and
> why _FillValue was set to zero. Marston, do you have any software,
> other than NCL, to display the file's metadata and check for the
> expected missing value a different way? I am not experienced with
> HDF4, so I can only raise suspicions, FWIW.
>
> --Dave A.
>
> On Mon, Jul 29, 2013 at 12:00 PM, David Brown <dbrown@ucar.edu> wrote:
>> Hi Marston,
>>
>> You cannot test a value that is set to the _FillValue for equality using e.g.: Data_quality .eq. 0. Instead you should use the 'ismissing' function, for example:
>>
>> where (ismissing(Data_quality), test_var = test_var@_FillValue, test_var)
>>
>> (assumes test_var is another variable in the file that has the same dimensionality as Data_quality)
>>
>> The other option in this case might be to delete the _FillValue attribute:
>>
>> delete (Data_quality@_FillValue)
>> where (Data_quality .eq. 0, test_var = test_var@_FillValue, test_var)
>>
>> This is in no way specific to the byte type.
>>
>> It is a feature of ncdump that values set to the _FillValue are printed as '_'. Again this is not specific to any type. If you don't like this you could use ncl_filedump instead.
>> -dave
>>
>>
>>
>> On Jul 29, 2013, at 11:09 AM, Marston Johnston <shejo284@gmail.com> wrote:
>>
>>>
>>> Hi,
>>>
>>> I'm working with CloudSat hdf4-eos files using NCL version 6.1.
>>> In the CloudSat file, the Data_Quality variable in the hdf file is of type "byte".
>>> Is there a function to check which byte is set? For example, how do I check other variable arrays using mask or where, with the condition that Data_quality is 0? I tried the function byte2flt, but this fails. The problem is that in the CloudSat docs, the Data_quality flag is set to 0 if the data is good. Otherwise the data is bad. After NCL reads the variable, the _FillValue is set to 0.
>>>
>>> Variable: Data_quality
>>> Type: byte
>>> Total Size: 20820 bytes
>>> 20820 values
>>> Number of Dimensions: 1
>>> Dimensions and sizes: [nray_2C_ICE | 20820]
>>> Coordinates:
>>> Number Of Attributes: 3
>>> _FillValue : 0
>>> unsigned : True
>>> hdfeos_name : Data_quality
>>>
>>> Another strange thing is that when the hdd file is converted to netcdf, the ncdump shows much of, if not all of the data as containing: '-', not values.
>>>
>>> Appreciate little info on how to treat byte arrays.
>>>
>>> /M
> _______________________________________________
> ncl-talk mailing list
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk

_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk
Received on Mon Jul 29 13:19:05 2013