[gdal-dev] hdf5image metadata problems

[Antonio Valentino]

Hi Alex,

Il giorno Thu, 16 Jun 2011 10:05:42 -0300
Alex Mantaut <alexmantaut at suremptec.com.ar> ha scritto:

> Hi Antonio,
> 
> For what I discussed with Frank it seemed that the expected behavior
> was to get the only the data asociated to that subdataset (plus some
> aditional data from root and the other groups) I wasn't sure untill
> you confirmated...
> 
> Well, right now when I open a specific subdataset it gets only the
> raster band asociated to that dataset, but when I try to open the
> metadata (with GetMetadata() or GetMetadataItem()) from that
> subdataset it opens the metadata from all the groups (as expected)
> but it doesn't get the metadata asociated to that subdataset... Did I
> do something incorrectly when opening the metadata from the
> subdataset?
> 
>  The line suggested in the ticket:
>         ReadGlobalAttributes( TRUE );
> 
> Was a way to get around the problem, but now that I'm sure that
> hdf5imagedataset doesn't need to read all the metadata, it's not a
> suitable solution to the defect...
> 
> Right now I found another way to get the metadata from the
> subdataset, by getting the rasterband first, and then asking for the
> metadata asociated to that raster band ( it seems a overly convoluted
> to get the metadata asociated to that subdataset...) I'm guessing
> that the expected behavior is to get the information directly through
> GetMetadata() directly...
> 
> regards
> 

Well, IMHO it is not convoluted. Associating "HDF5 dataset" metadata
tho the GDAL raster band just reflects the original HDF5 structure.

Even if HDF5 and GDAL data model are quite different we can assume,
IMHO, the following correspondence:

HDF5 file    --> GDAL dataset (HDF5Dataset class)
HDF5 Group   --> None (metadata are associated to GDAL dataset)
HDF5 Dataset --> GDAL Raster Band

HDF5 file can contain several datasets (with arbitrary shape) so the
GDAL subdataset mechanism is used to tell to the HDF5ImageDataset class
which is the "HDF5 dataset" the have to be mapped onto the GDAL raster
band.

I hope this is not too much confusing, with my poor english I'm not
able to explain it better :).


regards

> 
> 2011/6/15 Antonio Valentino <antonio.valentino at tiscali.it>
> 
> > Hi Frank, hi Alex,
> >
> > Il 15/06/2011 22:34, Frank Warmerdam ha scritto:
> > > On 11-06-15 03:50 PM, Alex Mantaut wrote:
> > >> Hi Frank:
> > >>              Thanks for the swift reply.
> > >>               Right now it opens the metadata asociated to the
> > >> root, and also
> > >> the metadata asociated with all the other groups, but it doesn't
> > >> open
> > the
> > >> metadata asociated to the specified element (bug?)
> > >
> > > Alex,
> > >
> > > It sounds like a defect to me, yes.
> > >
> > > I would suggest filing a ticket that carefully documents the
> > > problem with a supporting example file.
> > >
> > > Best regards,
> >
> > The current behavior looks fine to me.
> >
> > If one opens a specific subdataset then only one "HDF5 dataset
> > object" can be accessed and it is mapped on GDAL raster bans n. 1.
> > All other "HDF5 dataset object" in the h5 file are ignored by the
> > HDF5ImageDataset so there is no reason IMHO to make their metadata
> > available in some manner.
> >
> > Metadata associated to all HDF5 groups (including the root one) are
> > available in any case and accessible via GDAL dataset metadata.
> >
> > my two cents
> >
> > --
> > Antonio Valentino


-- 
Antonio Valentino