HDF5 Dimension Scales

[axelboc]

It would be nice to support HDF5's dimension scales. We've received multiple feature requests relating to those, including in a couple of recent emails. Dimension scales are apparently used quite extensively in NetCDF4 files, to describe how to plot datasets (axes, units, etc.).

In his email, Jean-Christophe describes, for instance, how to create a time-based dimension scale (which could then be "attached" to a dataset - e.g. values.dims[0].attach_scale(time)).

df_modified = pd.to_datetime(df.index.values) - time # Difference of time from a given date
df_modified_str = df_modified.total_seconds().to_numpy()
time_dset = group.create_dataset ('time', data=df_modified_str)
time_dset.attrs["long_name"] = "UTC Time"
time_dset.attrs["description"] = ModelHDFLevel4Lumina.TIME.__doc__    
time_dset.attrs["calendar"] = "standard"
time_dset.attrs["units"] = f"seconds since {time.strftime('%Y-%m-%d %H:%M:%S')}"
time_dset.make_scale('time')

More reading:

• Primer on HDF5 Dimension Scales on StackOverflow
• h5py documentation
• A blog post with a dump of a sample NetCDF4 file that shows HDF5 Dimension Scales.
• The NetCDF Climate and Forecast Conventions (cf. section 4.4. Time Coordinate, for the naming convention used in the units attribute above to indicate that a dimension scale dataset contains relative timestamps.)

[axelboc]

h5wasm@0.6.9 brings support for reading dimension scales.