missing_value, _FillValue are both mapped to NaNs
details are here:
send me an example file if you think somethings not working.
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.
-----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
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?
-------------------------------------------------------------------------------- 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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