[Qgis-user] FW: Inconsistent WFS layer requests

[Even Rouault]

Le mercredi 09 mars 2016 09:22:57, Thomas Colley a écrit :
> Hi
> 
> I mistakenly posted this to developer list instead of user yesterday, hope
> it's ok to post here too.
> 
> I am trying to troubleshoot a problem we're having with a WFS service in
> QGIS 2.14. I am loading in a layer with 'Only request features overlapping
> the current view extent' and have tried cached and uncached. The layer
> loads only 1 feature and that is not within the map canvas. I have used
> Wireshark to capture the requests and can see that QGIS is making the
> GetFeature request with no bbox parameter and a maxfeatures parameter set
> to 1.
> 
> In QGIS 2.12.2 the GetFeature request with no bbox and maxfeatures=1 is
> still made but then it is followed up with another GetFeature request with
> the correct bbox and all features are loaded onto the layer as expected. I
> am wondering if the maxfeatures=1 request is a probe to test that valid
> features are being returned before making the proper request but in 2.14
> the proper request never gets sent. Looking at the layer metadata in QGIS
> the layer source shows the correct request URL.
> 
> It's confusing as we have other WFS services which are working fine in
> 2.14. If I can narrow the issue down to being a problem with the service
> itself I can approach the supplier.

The request with maxfeatures=1 is done when the response to the 
DescribeFeatureType request couldn't determine if the geometry type is point, 
line or polygon. So it downloads a single feature and use its geometry type as 
the layer type.

So I guess there's a logic problem in the code in that probably rarely used 
code path.

Did you try doing a zoom in or zoom out or pan operation ? This might perhaps 
help triggering a new request (not sure though)

> 
> It's a commercial WFS but if anyone is able to test I can provide the
> connection URL.

I'm currently doing a major overhaul of the WFS provider ( 
https://github.com/qgis/QGIS-Enhancement-Proposals/issues/53 ) . That would be 
good if I could test your use case at some point. But not before a few weeks 
as the code isn't ready yet.

> 
> Below are details of the packets being sent from QGIS.
> 
> Thanks very much
> 
> Tom
> 
> WFS connection string:
> http://www.getmapping.com/web.feature.service/FeatureService.svc/xxxx/xxxxx
> /mastermap?
> 
> Layer source from Layer Properties > Metadata tab > Properties
> http://www.getmapping.com/web.feature.service/FeatureService.svc/xxxx/xxxxx
> /mastermap?SERVICE=WFS&VERSION=1.0.0&REQUEST=GetFeature&TYPENAME=topographi
> carea&SRSNAME=EPSG:27700&BBOX=274257.18611745559610426,195451.6365115281660
> 1098,274325.73425826861057431,195546.70830481656594202
> 
> Requests sent when adding WFS layer (caught by Wireshark):
> http://www.getmapping.com/web.feature.service/FeatureService.svc/xxxx/xxxxx
> /mastermap?SERVICE=WFS&VERSION=1.0.0&TYPENAME=topographicarea&BBOX=274257.1
> 8611745559610426,195451.63651152816601098,274325.73425826861057431,195546.7
> 0830481656594202&REQUEST=DescribeFeatureType
> 
> http://www.getmapping.com/web.feature.service/FeatureService.svc/xxxx/xxxxx
> /mastermap?SERVICE=WFS&VERSION=1.0.0&REQUEST=GetFeature&TYPENAME=topographi
> carea&SRSNAME=EPSG:27700&&MAXFEATURES=1
> 
> http://www.getmapping.com/web.feature.service/FeatureService.svc/xxxx/xxxxx
> /mastermap?SERVICE=WFS&VERSION=1.0.0&REQUEST=GetCapabilities&TYPENAME=topog
> raphicarea&SRSNAME=EPSG:27700&BBOX=274257.18611745559610426,195451.63651152
> 816601098,274325.73425826861057431,195546.70830481656594202

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