[QGIS-Developer] GetFeatureInfo: sensitivity on rendered geometry vs original geometry.

[Andreas Neumann]

Hi, 

I'd like to discuss an issue with GetFeatureInfo that we have with point
symbols. 

(Point) symbols can have different sizes (sometimes rather large),
different anchor points and sometimes even with offset away from the
original feature geometry. Often, the rendering of the point symbol
differs substantially from the original point geometry. 

Now, our issue is that GetFeatureInfo often fails miserably in such
cases. People try to click on the visible symbol, which doesn't
correspond to the original geometry. 

One such example WMS: 

https://services.geo.zg.ch/ows/Abfallsammelstellen 

The symbols are rather large, but the anchor point is at the bottom of
the symbol. Users now think that they can click anywhere on the symbol,
but in fact they can only click on the original geometry at the very
bottom of the symbol, taking into account the FI_POINT_TOLERANCE
parameter. 

Things get even worse when one wants to identify points that are
displayed using the point displacement renderer. There, GetFeatureInfo
is only sensitive on the center point, and not at all at the rendered
points at a completely different position. 

Now my question: could we improve QGIS server that GetFeatureInfo
responds to the bounding boxes of the rendered geometries (as opposed to
the raw geometries), taking into account sizes, offsets, etc. 

Would this be technically possible?  

Would others also think that this is useful to have? 

Or would this even contradict OGC standards? 

Do other WMS servers implement such behaviors (Geoserver, UMN)? 

Thanks for the discussion, 

Andreas
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