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[netCDFJava #HMD-769692]: GridDataset has zero size for ensemble data



Hello,

This one took some real digging.

The problem with the dataset is that GridDataset isn't identifying the "ens" 
variable as an Ensemble coordinate axis. That, in turn, causes none of the grid 
variables to be identified as grids, because they're all dimensioned by the 
"ens" dimension, and the coordinate system stack doesn't know which axis that 
dimension corresponds to.

It turns out that in order for a variable to be identified as an Ensemble 
CoordinateAxis in a gridded dataset:
* it must include a "_CoordinateAxisType=Ensemble" attribute OR
* it must include a "standard_name=ensemble" attribute AND the dataset must 
have a "Conventions=CF-1.X" global attribute.

The NOMADS dataset you linked to doesn't meet either requirement. You could say 
that's a defect in the data that NOAA should address, but really, I think that 
ensemble axis detection is much too narrow. I've made a ticket about that on 
GitHub, if you want to follow our progress: 
https://github.com/Unidata/thredds/issues/860

For now, you can use NcML to add the necessary attribute (see attached 
example). In your code, try opening "foo.ncml" instead.

Cheers,
Christian

Ticket Details
===================
Ticket ID: HMD-769692
Department: Support netCDF Java
Priority: Normal
Status: Closed
===================
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Attachment: foo.ncml
Description: Binary data