[gdal-dev] Possible to test for a layer capability before creating a layer?

[Ari Jolma]

19.02.2016, 02:23, Even Rouault kirjoitti:
> Le vendredi 19 février 2016 00:55:21, Nyall Dawson a écrit :
>> Hi all,
>>
>> I'm aware that for drivers I can use OGR_Dr_TestCapability to
>> determine whether a particular driver as a specific capability. But is
>> there anyway to test whether a specific driver also has support for a
>> layer capability?
>>
>> The situation is that I'd like to populate a list with all available
>> OGR drivers for which a created layer would then be able to support
>> SequentialWrite, DeleteFeature, RandomWrite and CreateField.
>>
>> What would be the best way to go about this?
> There seems to be growing interests for such topic (see yesterday similar
> thread : https://lists.osgeo.org/pipermail/gdal-dev/2016-February/043782.html
> )
>
> The way to go is to add such capability flags at the driver metadata level.
> This is now possible since GDAL 2.0 since OGR drivers can expose arbitrary
> metadata items.
> What has to be done :
> - define which capabilities must be exposed
> - enhance drivers to advertize them

In this case the question is about existing layer capabilities. One 
obstacle to testing them is that there is usually no way to create 
"blank" or minimal layer objects. For example Shapefile layer 
constructor requires all kinds of information and it represents an 
actual file (which can be in memory, though).

Blank or minimal layer objects could be useful as they can answer 
capability questions - the TestCapability method usually requires no or 
only minimal property information (is the layer read only or not, is 
filtering on).

Hm. Since the property information plays a part, the capability is not 
always a simple on/off issue, but the answer to a question whether a 
layer has a specific capability can also be "it depends" if you only 
know the driver.

Ari

>
>> Nyall
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