[gdal-dev] Formalizing GDAL "file name" syntax in an RFC?

[Sean Gillies]

Even,

I agree that there is an untidy legacy. And it's probably not worth
formalizing the marginal filenames and connection strings. How about an RFC
and formal syntax only for hierarchical datasets then? It seems like this
is the direction the industry is growing.

Yes, I think a formal syntax for /vsi filenames would be useful. It's
almost done already, right? Only in prose, not ABNF (or whatever), but
that's a good start.

On Thu, Sep 14, 2023 at 10:21 AM Even Rouault <even.rouault at spatialys.com>
wrote:

> Sean,
>
> It is far from obvious to me to find a universal pattern that would fit
> existing and future use cases. If we would find a universal syntax, there
> would be the problem of deciding what to do with code that doesn't match
> it: support only new way (breaking external code),  or supporting both old
> and new ways (additional complexity in our code base)
>
> How would we deal with the existing practices which are very diverse ?
> Examples:
>
> - True filenames (most of the drivers)
>
> - Database based drivers:
>
> PG:"dbname='databasename' host='addr' port='5432' user='x' password='y'"   (Postgis vector)PG:"[host=''] [port=''] [dbname='' [user=''] [password=''] [schema=''] [table=''] [column=''] [where=''] [mode=''] [outdb_resolution='']"  (Postgis raster, consistent with previous one)
> MYSQL:dbname,user="userid",password="password",host=x,port=y
> OCI:username/password at host_name:port_number/service_name:MY_SCHEMA.MY_VIEWgeoraster:<user>{,/}<pwd>{,@}[db],[schema.][table],[column],[where]
> georaster:<user>{,/}<pwd>{,@}[db],<rdt>,<rid>
>
> - Web services (some of them also accept plain filenames that are .xml
> files describing the service and parameters)
>
> WMS:http://demo.opengeo.org/geoserver/gwc/service/wms?SERVICE=WMS&VERSION=1.1.1&
>                             REQUEST=GetMap&LAYERS=og%3Abugsites&SRS=EPSG:900913&
>                             BBOX=-1.15841845090625E7,5479006.186718751,-1.1505912992109375E7,5557277.703671876&
>                             FORMAT=image/png&TILESIZE=256&OVERVIEWCOUNT=25&MINRESOLUTION=0.0046653459640220&TILED=true"
> (note the mix of pure WMS GetMap request query parameters + GDAL specific properties TILESIZE, OVERVIEWCOUNT, MINRESOLUTION)
>
> WCS:http://194.66.252.155/cgi-bin/BGS_EMODnet_bathymetry/ows?VERSION=1.1.0&coverage=BGS_EMODNET_CentralMed-MColWFS:http://www2.dmsolutions.ca/cgi-bin/mswfs_gmapOAPIF:https://www.ldproxy.nrw.de/rest/services/katasterWMTS:http://maps.wien.gv.at/wmts/1.0.0/WMTSCapabilities.xml,layer=lb
> ( layer= is GDAL specific)
>
>
> - Raster subdatasets (whether to surround filename with double quotes is
> driver specific)
>
> NITF_IM:{image_number}:{filename}
>
> NITF_TOC_ENTRY:{product_type}_{chartname}_{scale}_{somenumber}_{anothernumber}:GNCJNCN/rpf/a.toc
> ECRG_TOC_ENTRY:{product_name}:{disk_name}:{scale}:{filename}
> GTIFF:{directory_number}:{filename}
> GTIFF:off:{directory_offset}:{filename}
> GPKG:{filename}:{tablename}
> netCDF:{filename}:{variable_name}
> HDF5:{filename}:{dataset_path}
> ZARR:{filename}  (mostly when filename is /vsicurl/ and we don't have a
> ReadDirectory() API)
> ZARR:{filename}:{path_to_array}
>
> ZARR:{filename}:{path_to_array}:{third_dim_index}[:{fourth_dim_index}[:{fifth_dim_index}...]]
>
> - Other syntax
>
> vrt:// connection string (
> https://gdal.org/drivers/raster/vrt.html#vrt-connection-string) . e.g.
> vrt://my.tif?bands=3,2,1
>
> Do you have also /vsi syntax in mind ?
>
> Even
>
> Le 14/09/2023 à 17:14, Sean Gillies a écrit :
>
> Hi all,
>
> In https://github.com/OSGeo/gdal/pull/8155#issuecomment-1704923263 I
> think I see (for the first time?) the beginning of a specification of the
> syntax for GDAL "file names". I think it would be helpful if there was an
> RFC for this.
>
> I'm sure a lot of applications construct GDAL file names without much
> understanding of what's correct or incorrect. A formal spec could help make
> it more likely that anyone can construct a valid filename on the first try.
>
> A stretch goal for the RFC could be to come up with a syntax that is
> sufficiently general that authors of new format drivers don't have to
> create their own new idiosyncratic file names.
>
> --
> Sean Gillies
>
>
-- 
Sean Gillies
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