[gdal-dev] Multiple extensions in GDAL_DMD_EXTENSION ?

[Frank Warmerdam]

On Tue, Feb 19, 2013 at 9:39 AM, Etienne Tourigny
<etourigny.dev at gmail.com> wrote:
> It would be nice to be able to specify many extensions in a
> comma-separated list such as "nc,cdf,nc4". It can probably be done
> (metadata is just a string), but isn't standard.
>
> The Gdal driver tutorial states:
> GDAL_DMD_EXTENSION: The extension used for files of this type. If more
> than one pick the primary extension, or none at all. (optional)
>
> It could be beneficial to extend this definition for multiple
> extensions separated by comma.

Etienne,

The challenge is to do this without breaking lots of applications that
expect it to be a single extension.  If we were to pursue this, I'd
almost prefer to add GDAL_DMD_EXTENSION_LIST as a list of extensions
that relate to this driver, and GDAL_DMD_EXTENSION would be the
primary or preferred extension.

But I'm still not all that keen.  I see the GDAL_DMD_EXTENSION as
existing primarily so that applications can prepare a reasonable
default filename when creating a file.  For this having a list of
extensions is not helpful.

People *usually* want a list of extensions so they can automatically
categorize the format of files on disk or to filter to only show
extensions they think GDAL supports.  I find this practice abhorrent!
 GDAL is based on the idea that file formats are discovered by
inspecting file contents rather than based on extension and I don't
want to make it too easy for applications to ignore this principle and
revert to extensions.

One other use that extensions are used for is to make it easy for a
user to filter down files in a file browser to just one format.  I
can't think of any time I've found this useful.  But with GDAL there
are so many formats that these "list of formats" filter dohickyies are
usually completely unusable.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Software Developer