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Re: interpretation of missing_value by ncWMS

Hi all:

missing_value, _FillValue are both mapped to NaNs

details are here:


send me an example file if you think somethings not working.


On 4/24/2012 11:00 AM, Jon Blower wrote:
Hi Sean,

I must admit I hadn't appreciated the semantic distinction between 
missing_value and _FillValue.  However, I assumed that ncWMS would treat both 
of these essentially the same and recognize missing_value as data outside the 
dataset.  The Java-NetCDF libs automatically recognise these and convert data 
to NaN (I thought).

I've copied to John Caron, who can hopefully comment on whether Java-NetCDF 
treats the attributes differently.

Cheers, Jon

-----Original Message-----
From: Gaffney, Sean P. [mailto:address@hidden
Sent: 24 April 2012 10:20
To: Jon Blower
Subject: interpretation of missing_value by ncWMS

Hi Jon,

I've just found out from John Caron that the attribute missing_value is not 
being deprecated in the CF conventions so is an acceptable CF attribute. A lot 
of the feedback I've had from the community has been that _FillValue should 
only be used to define the actual default value used to generate the file 
structure before it was populated, and that if there are any actual absent data 
values, these should be indicated using missing_value. I'd puzzled over this 
because I thought the missing_value attribute was being lost, but this 
obviously is no longer the case.

My understanding of how the ncWMS works at the moment is that it doesn't 
recognise missing_value as data outside the dataset - I've had this problem 
with the data that Helen sent me, where she had left out _FillValue but 
supplied missing_value and the points covering land surface weren't being made 

Therefore, my question to you is, can the ncWMS be made to treat missing_value 
in the same way it treats _FillValue, so that if it encounters either one, it 
will regard them as a NaN and make the cell of the model transparent for 
visualisation purposes?



Sean Gaffney
Data Scientist
British Oceanographic Data Centre
Joseph Proudman Building
6 Brownlow Street
L3 5DA
+44 (0)151 795 4950

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