[gdal-dev] Call for discussion for "RFC 43 GDALMajorObject::GetMetadataDomainList()"

[Even Rouault]

Le dimanche 20 octobre 2013 11:38:24, xavier lhomme a écrit :
> Hi
>   Is there a way to export Metadata in a XML form (ISO 19139 XML
> implementation of ISO 19115 ) ?

Xavier,

This is clearly out of the scope of this RFC.

Apart from a few basic items ( raster dimensions, tiling, geotransform/GCP, 
SRS ), GDAL drivers currently expose metadata as close as possible as the way 
they are encoded in the format they deal with (and GDAL probably predates the 
current metadata standards). By searching a bit, I've found a few projects 
(but I haven't actually tried them) that would expose GDAL metadata in 
standard ways :
  * a QGIS plugin : MetaTools . https://github.com/nextgis/metatools 
  * MetaGETA : Python scripts  . https://code.google.com/p/metageta/
  * Metadata crawler of Geonetwork . 
http://trac.osgeo.org/geonetwork/wiki/crawler
  * ...

MetaGETA seems interesting since it has specialized code for different GDAL 
drivers to extract particular metadata items, in addition to the standard 
metadata.

As far as if this would be interesting to have in GDAL itself, this is an open 
question. I'm not very well versed in metadata standards, but my impression is 
that there are many of them (ISO 19139, that seems to have had several 
versions, and that can have custom profiles apparently, FGDC, ...), and we 
probably wouldn't want to have to implement all of them in each driver.

(Annectodicaly GDAL is a consumer of ISO 19115 in the BAG driver, to extract 
georeferencing.)

I'm also wondering to which extent it is possible to generate valid XML 
metadata documents in an automated way, from the information found in the 
dataset. I'm thinking particularly to mandatory metadata items whose content 
couldn't be found in the dataset.

Even

> 
> xav
> 
> 
> 2013/10/19 Even Rouault <even.rouault at mines-paris.org>
> 
> > Hi,
> > 
> > This is a call for discussion for "RFC 43
> > GDALMajorObject::GetMetadataDomainList()" :
> > 
> > http://trac.osgeo.org/gdal/wiki/rfc43_getmetadatadomainlist
> > 
> > Beginning of the RFC inline :
> > """
> > 
> > == Summary ==
> > 
> > This (mini)RFC proposes a new virtual method, GetMetadataDomainList(), in
> > the
> > GDALMajorObject class (and a C API) to return the list of all available
> > metadata domains.
> > 
> > == Background ==
> > 
> > GDALMajorObject currently offers the GetMetadata() and GetMetadataItem()
> > methods that both accept a metadata domain argument. But there is no way
> > to auto-discover which metadata domains are valid for a given
> > GDALMajorObject (i.e. a dataset or raster band). This make it impossible
> > to have generic code
> > that can exhaustively discover all metadata in a dataset/raster band.
> > 
> > [...]
> > 
> > """
> > 
> > Best regards,
> > 
> > Even
> > 
> > --
> > Geospatial professional services
> > http://even.rouault.free.fr/services.html
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