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

[Alessandro Pasotti]

On Fri, Apr 12, 2019 at 3:53 PM René-Luc Dhont <rldhont at gmail.com> wrote:

> Hi Andreas,
>
> I think QGIS Server has to use the rendered geometries to identify Feature.
>

Hi René,

Yeah, I also though that's the only solution, what scares me is the
performances cost, because we would need to render and check each layer
individually.



> Is it possible to get the  point layer to polygon rendred layer ?
>

I don't follow you, can you explain what's in your mind?



>
> Regards,
> René-Luc
>
> Le 12/04/2019 à 15:43, Andreas Neumann a écrit :
>
> 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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-- 
Alessandro Pasotti
w3:   www.itopen.it
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