> There are two ways VisAD can handle file metadata:
>
> 1) Sometimes the file form adapter includes relevant metadata as part of
> the data object. You can determine whether this is happening in the
> VisAD SpreadSheet by bringing up the Edit Mappings dialog, and taking a
> look at the MathType. If it is big and complex, chances are that it
> represents a large tuple containing both pixel data and various metadata
> parameters. I believe (although I am not certain) that the netCDF Plain
> form behaves this way. Unfortunately, I don't think the FITS form does.
>
> 2) To generalize the file metadata concept, I recently created an
> optional interface for VisAD file form adapters:
> visad.data.MetadataReader. It allows the file form to provide a
> Hashtable containing all metadata extracted from the file, represented
> as key/value pairs. (Of course, what this metadata is completely depends
> on the file format.) I have implemented MetadataReader for the file form
> adapters in visad.data.bio, but most other file forms do not yet support
> it. Whether it gets implemented for other formats will depend on user
> interest and VisAD developers' time availability.
Personally I prefer approach 1, including file metadata
in the DataImpl object, because then all file data is
uniformly accessible via the VisAD data model. But of
course you are free to use either approach in an open
architecture like VisAD.
Cheers,
Bill
