Hi all,
On Tue, Oct 4, 2011 at 9:58 AM, Ivan Lucena <ivan.luc...@pmldnet.com> wrote:
> Frank,
>
>> -------Original Message-------
>> From: Frank Warmerdam <warmer...@pobox.com>
>> To: Daniel Morissette <dmorisse...@mapgears.com>
>> Cc: gdal-dev@lists.osgeo.org
>> Subject: Re: [gdal-dev] Resquest for comments (RFC 36)
>> Sent: Oct 03 '11 21:04
>>
>> On Mon, Oct 3, 2011 at 6:14 PM, Daniel Morissette
>> <dmorisse...@mapgears.com> wrote:
>> > I like the idea, especially since it can increase performance in some
>> cases.
>> > However unless I'm mistaken the proposed patch seems to fall back on the
>> > regular test-open loop when the GDALOpenInternal() call with the explicit
>> > driver name failed, no matter why it failed. e.g. I specify the invalid
>> > "hfa:test.tif" open string, then I should get a NULL return value and not
>> a
>> > handle to a TIFF file.
>>
>> Daniel,
>>
>> I believe that is because it is hard to know if HFA:test.tif was really
>> something other than a request for the HFA driver. It could actually
>> be a file named "HFA:test.tif" or it could be that another driver happens
>> to use the HFA: prefix to mean something. I believe this is an
>> effort to avoid failure in these cases.
>
> I think that the concerns that Daniel and Jukka has expressed are legit.
>
> As I explain to Jukka. It might not be a problem but it is still feels like a
> dirt trick. I mean, the "fall back" strategy.
>
> So it would be better to do this instead:
>
> {{{
> GDALOpenInfo oOpenInfo( pszFilename, eAccess );
> if ( oOpenInfo.bStatOK == false && strstr( pszFilename, ":" ) != NULL )
> {
> return GDALOpenInternal( oOpenInfo );
> }
> return GDALOpenInternal(oOpenInfo, papszAllowedDrivers);
> }}}
>
> And implement any kind of driver-specific string convention inside the
> function.
>
>> > The patch would need to be reworked for this, but I think that if the
>> > GetDriverByName() call succeeds (i.e. the driver name prefix is recognized
>> > by GDAL) and the call to poDriver->pfnOpen() fails then we should return
>> > NULL to the application code (and not fall back on the test-open loop).
>> > OTOH, if the GetDriverByName() lookup failed, then we should fall back on
>> > the test-open loop.
>
> But as Frank mentioned, we do have some drivers that use unlawful driver
> names, like GTIFF_RAW. For example, one driver that I wrote is officially
> called "georaster:" but it does accept "geor:" and people got used to that
> simplification. What we could do is to create a list of driver-nickname
> extracting information from a new driver metada entry.
IMHO this should be added by each driver in the GDAL_Register<driver>
functions, and the driver's name be added automatically to this list,
without any changes.
>
>> >
>> > Also, if we implement this mechanism in GDAL, then we'd have to provide it
>> > in OGR as well to be consistent.
>>
>> I'm not convinced that this is necessary. I have had a hope for
>> some time to provide a standard way of binding up open options,
>> including the driver name, for OGR as demonstrated by a
>> request like:
>>
>> @driver=ingres,dbname=test
>>
>> One objection I had previously to Ivan's proposal is that I'm
>> interested in pursuing this general purpose mechanism for
>> many open options in OGR and in GDAL. But since I haven't
>> gotten to it for so long there is no point in holding up Ivan's
>> fairly straight forward change. Nevertheless, I'm hesitant to
>> push his change to OGR unnecessarily.
>
> I like that idea and I think it would address most of the concerns.
>
> It could like that, I guess:
>
> $ gdalinfo driver=gtiff,landsat1.tif
> $ gdalinfo driver=gtiff,gtiff_raw:landsat1.tif
>
> It is not very user friendly (just because it requires more writing) but the
> intention is to be script-friendly and app-friendly anyway. Right?
As there are already a number of drivers which accept the
DRIVER:filename syntax, (therefore users and applications already use
that syntax) I would recommend using that syntax for the fast
detection also.
Perhaps both syntaxes could be valid, in order to accommodate OGR also?
1) <driver>:<filename> (e.g. gtiff:landsat1.tif)
2) driver=<driver>,<filename> (e.g. driver=gtiff:landsat1.tif)
I would add my 2cents and suggest that unusual filenames like
"hfa:example_file.img" and "@driver=ingres,dbname=test.tif" are rare,
and a fallback to the (slower) detection mecanism in these cases won't
be detrimental on average.
>
> That would require minimal change and it would be backward compatible:
>
> {{{
> GDALOpenInfo oOpenInfo( pszFilename, eAccess );
> if ( oOpenInfo.bStatOK == false && EQUALN( pszFilename, "driver=", 7 ) )
> {
> return GDALOpenInternal( oOpenInfo );
> }
> return GDALOpenInternal(oOpenInfo, papszAllowedDrivers);
> }}}
>
> We just need to load the driver informed and pass the string that comes after
> the comma as the pszFileName. No strips, not tricks, plain and simple.
>
> I could write a patch and change the RFC if you want.
>
> Regards,
>
> Ivan
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