[gdal-dev] Re: WFS driver, ogrinfo and GetFeature

[Jukka Rahkonen]

Even Rouault <even.rouault <at> mines-paris.org> writes:

> 
> >
> > I am thinking as a WFS server admin and I cannot comment out the line
> > from those who are possibly using our services with GDAL. I am  not
> > causing so much trouble for myself :)
> >
> > I have set maxFeatures to 100000 on the server side. It will mean that the
> > accurate extents method of gdal will calculate them for the first 100000
> > features and with our layers which are spatially ordered the result will
> > be much more wrong than if using and reprojecting the advertised extents.
> >
> > I would say that if WFS 1.1.0 server is answering for the first
> > resulttype=hits query that there are 100000 features to come then ogrinfo
> > should be able to know that it could be expensive to get them all with
> > the next resulttype=features request.
> >
> > I have been thinking that WFS developers should never test anything
> > against WFS feature types containing less than one million polygons.
> > Testing against World boundaries does not show the whole picture.
> 
> Is your server available from the web ? If so, I could have a look on how 
the
> advertized extent could be used. Ah, and what WFS server and which version
 of it
> are you using ?
> 
> I'm thinking that we could try to use the advertized extent by default, 
and if
> needed, the user could define an environment variable to have the extent
> computed on all features. That way, the default behaviour would be more
> reasonable.
> 

I sent the server url as a private mail. Afterwards it came into my mind that
for counting the exact extents it would be enough to select just the geometry
property and not all the attributes. That would save a lot of traffic with
attribute rich feature types. Or does DGAL want to read all the attributes too
and resolve the schema that way instead of using schema returned by
DescribeFeatureType? GDAL does not necessarily understand the latter if it is
presenting some odd application schema.

On the other hand, if gdal makes a full GetFeature when checking the extents of
the layer, as a server admin I would love to see it to cache the result in some
disk cache, Spatialite database or whatever instead of making the same total
GetFeature later. 

-Jukka Rahkonen-