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Bringing this back up again, now that I see that _NCProperties is included in the documentation under "Attribute Conventions" [1]. Is there are a good way to handle cases where there is no valid netcdflib version to include here, because the file wasn't written using netcdf-c? What I've been doing is including h5netcdfversion=X.Y.Z in the _NCProperties attribute instead of netcdflib=X.Y.Z. I'm thinking now that I'd also like to include versions of other libraries used to generate the file (e.g., h5py). Does that seem reasonable? Or should I rather drop unexpected names altogether? At the very least, I don't think I can include any sensible netcdflib version. [1] http://www.unidata.ucar.edu/software/netcdf/docs/attribute_conventions.html On Sat, Apr 30, 2016 at 12:45 PM, dmh@xxxxxxxx <dmh@xxxxxxxx> wrote: > This will be documented in the existing documentation. > At some point, it needs to be added to the netcdf NASA spec > (https://earthdata.nasa.gov/standards/netcdf-4hdf5-file-format). > =Dennis Heimbigner > Unidata > > On 4/29/2016 10:39 PM, Stephan Hoyer wrote: > >> What is the specification you're planning to use for the value of the >> _NCProperties attribute? We'd like to able to generate compliant netCDF4 >> files with h5netcdf, which uses HDF5 directly to write netCDF4. >> >> I guess my main request is to not assume that only netCDF-C will write >> _NCProperties attributes, and to ensure that netCDF-C and the specification >> are flexible enough to allow for different implementations, maybe even >> hypothetical implementations not using the HDF5 libraries at all. >> >> Thanks, >> Stpehan >> >> On Fri, Apr 29, 2016 at 8:32 PM, dmh@xxxxxxxx <mailto:dmh@xxxxxxxx> < >> dmh@xxxxxxxx <mailto:dmh@xxxxxxxx>> wrote: >> >> I am about to commit a pull request for the netcdf-c library having to >> do with identifying the provenance and format of netcdf-4 files, >> and specifically targeted at detecting netcdf-4 files from HDF5 files. >> >> This provenance consists of the following information. First, there is >> a hidden, persistent, attribute names _NCProperties. It specifies the >> library versions of the netcdf library and the hdf5 library used to >> create the file. This attribute never changes during the lifetime >> of the >> file (unless modified deliberately thru the hdf5 API). >> >> Second, there are two special, non-persistent, attributes that are >> computed from information already in the file. >> 1. _SuperblockVersion >> 2. _IsNetcdf4 >> Non-persistence means these attributes do not actually appear in the >> file. and are computed from other info already in the file. >> >> The _SuperblockVersion attribute is a single integer giving the >> version >> number (currently 0-3) of the superblock in the hdf5/netcdf-4 file. >> >> The _IsNetcdf4 attribute is a single integer 0/1 indicating if the >> file >> has various tags indicating it was produced thru the netcdf-4 API. >> This >> is computed by using the HDF5 API to walk the file to look for >> attributes specific to netcdf-4. False negatives are possible for a >> small subset of netcdf-4 files, especially those not containing >> dimensions. False positives are (I think) only possible by deliberate >> modifications to an existing HDF5 file thru the HDF5 API. For >> files with >> the _NCProperties attribute, this attribute is redundant. For files >> created prior to the introduction of the _NCProperties attribute, this >> may be a useful indicator of the provenance of the file. >> >> These three attributes are hidden in the sense that they can only be >> accessed thru the netcdf-C api calls via the name. They have no >> attribute number and will not be counted in the number of global >> attributes in the root group. >> >> The simplest way to view these attributes is to use the -s flag to the >> ncdump command. >> >> Comments are welcome. >> >> =Dennis Heimbigner >> Unidata >> >> _______________________________________________ >> netcdfgroup mailing list >> netcdfgroup@xxxxxxxxxxxxxxxx <mailto:netcdfgroup@xxxxxxxxxxxxxxxx> >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/mailing_lists/ >> >> > _______________________________________________ > netcdfgroup mailing list > netcdfgroup@xxxxxxxxxxxxxxxx > For list information or to unsubscribe, visit: > http://www.unidata.ucar.edu/mailing_lists/ >
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