Re: ncl-talk nan in dataset, again

[1] _FillValue is what the CF convention states should be used
     to indicate missing values. Further, Unidata says the same thing.
     NCL recognizes _FillValue only.

[2] missing_value is a COARDS convention attribute. It has no
     special status under CF or within NCL.

[3] _MissingValue, etc....., mean nothing to any known software

[4] By rule, the type of the _FillValue should be the same as
     the variable with which it is associated. However, there is
     nothing in the netCDF software to prevent this from happening.

[5] NCL does try to be 'helpful' in the following way. When a variable
     is read and NCL sees it has a missing_value attribute but
     no _FillValue, NCL will assign an virtual _FillValue' attribute.
     NCL checks the type of the missing_value attribute and the type
     of the associated variable. If they are the same, NCL creates
     the _FillValue attribute; if the are different and NCL can
     coerce the missing_value to the type of the variable, NCL will
     do it. If not, you get the warning message indicated earlier.
     This is *not* an NCL problem. The file creators 'screwed up'.
     NCL can be used to address the issue but it must be done manually.

[6] NCL can check for NaNs and replace the values.
     http://www.ncl.ucar.edu/Document/Functions/Built-in/isnan_ieee.shtml
 
http://www.ncl.ucar.edu/Document/Functions/Built-in/replace_ieeenan.shtml

On 10/10/11 10:32 PM, donna Cote wrote:
> Yep, this looks interesting (disappointingly so).
> <snip>
> (190) nan
> (191) nan
> (192) nan
> (193) nan
> (194) nan
> (195) nan
> (196) nan
> (197) nan
> (198) -12.120189666748
> (199) -11.890799522400
> (200) -11.747349739075
> (201) -11.658637046814
> (202) -11.644246101379
> (203) -11.677687644958
> <snip>
>
> I shouldn't have doubted you when you said there were nan values in this
> data. Even after getting the _FillValue set. Maybe declare this dataset
> as unusable?
>
> Good luck,
> Donna
>
> On 10/10/11 6:31 PM, ncl-talk-request@ucar.edu wrote:
>> Date: Mon, 10 Oct 2011 17:57:52 -0500
>> From: Gerald Creager<gerry.creager@tamu.edu>
>> Subject: nan in dataset
>> To:"ncl-talk@ucar.edu"<ncl-talk@ucar.edu>
>> Message-ID:<4E937870.4070005@tamu.edu>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> Looks like a dataset I'm working with is malformed, with a
>> 'missing_value' but no __MissingValue provided.. In fact, none of the
>> variables have a "normal" __MissingValue and I get some ugly warmings
>> such as:
>> warning:NetOpenFile: MissingToFillValue option set True, but
>> missing_value attribute and data variable
>> (sea_floor_depth_below_sea_level) types differ: not adding virtual
>> _FillValue attribute
>>
>> I'm considering adding model8Ssh@_MissingValue=-9999 to see if this
>> resolves the problem but somehow, with this dataset, one never knows.
>>
>> Short form, I'm not getting any indication that the values are going to
>> plot and I'm stuck again.
>>
>> Thanks, Gerry
>> -- Gerry Creager -- gerry.creager@tamu.edu Texas Mesonet -- AATLT, Texas
>> A&M University Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
>> Office: 7607 Eastmark Drive, Suite 112, College Station, TX 77840
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Received on Tue Oct 11 06:23:54 2011