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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Ben Caradoc-Davies <ben@anonymised.com>
Director
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New Zealand