Thanks, Ben. I'll see where what can be done with these netCDF issues.
Can you suggest the most appropriate place for variable attribute
information to be passed from the file reading step to the
NetCDFOutputWriter? One candidate appears to be the Grid2DCoverage
properties but I would like to hear from someone with better knowledge of
the codebase.
Thanks,
Aaron
On Fri, Dec 9, 2016 at 8:21 PM, Ben Caradoc-Davies <[email protected]> wrote:
> Aaron,
>
> I can confirm your findings. Note that the absence of a _FillValue implies
> that, as far as I know, the default for that data type is used. I have had
> user feedback that an explicit _FillValue is preferred to make the file
> more self documenting and to reinforce its use a missing value (and I think
> some also like a matching missing_value attribute).
>
> There are more WCS NetCDF output problems:
>
> - The GeoServer web UI lacks a means to set variable attributes for NetCDF
> output; only global attributes can be set.
>
> - The dimension Units setting appears to be ignored; Unit Symbol being
> used instead.
>
> - Custom dimension units are encoded as "FIXME" when not set.
>
> - There is no way to set other attributes on dimensions, despite some of
> these being mandatory for CF-1.6 compliance, such the the positive
> attribute for vertical dimensions. The lack of attribute support is a
> killer when using a vertical sigma coordinate because there is nowhere to
> record the formula_terms that define it.
>
> The dimension problems become more evident when using ImageMosaic to add
> extra dimensions. There is no point setting a global Conventions until the
> above issues are addressed and CF-1.6 compliance is possible.
>
> Contributions to improve the fidelity and configurability of NetCDF output
> would be most welcome.
>
> Kind regards,
> Ben.
>
> On 10/12/16 11:30, Aaron Braeckel wrote:
>
>> Hello,
>>
>> GeoServer 2.9.1 and most other recent versions seem to lose some netCDF
>> (netcdf-extension) and GRIB (grib-extension) metadata on variables when
>> the
>> data is retrieved as netCDF (netcdf-out-extension). Note that I am using
>> netCDF terminology throughout this email.
>>
>> For example, in the gs-netcdf-out module (master/today)
>> WCSNetCDFTest::testRapNativeGribRotatedPole() reads in the
>> rap-native.grib2
>> file and writes it out as netCDF. I've attached the CDL of the input and
>> output for each, and the most important information that is missing from
>> the Temperature_surface variable in the output is:
>>
>> - The "coordinates" attribute
>> - Grib_* attributes (useful to some consumers)
>> - The "long_name" attribute
>> - And it appears all attributes on variables other than "units",
>> "_FillValue", and a few others
>>
>> Global attributes (such as "Originating_or_generating_Center") are also
>> missing and important, but these can be configured for inclusion through
>> the GeoServer web UI.
>>
>> I am familiar with the netCDF Java API and happy to dig in to the code and
>> submit a patch, if appropriate, but I am a new developer to GeoServer and
>> it is unclear to me how these attributes on the variable might best be
>> passed along to the NetCDFOutputManager. Setting GridCoverage2D
>> "properties" might be a candidate but I want to check with those more
>> familiar with the codebase to be sure.
>>
>> Do you have any suggestions or cautions for adding this capability to
>> GeoTools/GeoServer?
>>
>> Thanks,
>> Aaron
>>
>>
>>
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>>
>> _______________________________________________
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>>
> --
> Ben Caradoc-Davies <[email protected]>
> Director
> Transient Software Limited <http://transient.nz/>
> New Zealand
>
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