Re: interpretation of missing_value by ncWMS

Hi all:

missing_value, _FillValue are both mapped to NaNs

details are here:

http://www.unidata.ucar.edu/software/netcdf-java/v4.2/javadoc/ucar/nc2/dataset/EnhanceScaleMissing.html

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

John

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 
> transparent.
>
> 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?
>
> Cheers
>
> Sean
>
> --------------------------------------------------------------------------------
> Sean Gaffney
> Data Scientist
> British Oceanographic Data Centre
> Joseph Proudman Building
> 6 Brownlow Street
> Liverpool
> L3 5DA
> UK
> +44 (0)151 795 4950
>
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