[Qgis-developer] Handling of fuzzy boundaries

[Stefan Keller]

Dear Tim

Thanks for your reply. I'm one of the coaches of this thesis.

> Right - one could probably apply blur effects and similar to lines to
> represent their fuzzyness - Qt4 already has some infrastructure for this
> kind of thing e.g.
> http://doc.qt.nokia.com/4.6/qgraphicsdropshadoweffect.html#details

=> Is this also accessible through Python (plugin)?

> I'm not sure about using two separate layers as you describe above - it
> might be nicer to make fuzziness simply an attribute of the feature -
> though I guess it doesnt cope well for the scenario where individual
> segments of a feature have different fuzziness levels...

In fact, the fuzziness attribute has to be somehow 'attached' to segments.
In the use cases I know often there are some segments along the
boundary which are not fuzzy but crisp on purpose.
An example might be where a street touches the fuzzy feature.
So since segments of a polygon can't be accessed from 'outside' one
solution might be to have a "shadow" layer which consists of
polylines.

=> Do you have another idea on how to implement such "line segment
atttributes" in QGIS?

Yours, S.


2010/9/27 Tim Sutton <lists at linfiniti.com>:
> Hi
>
> On Wed, 2010-09-22 at 17:47 +0200, Annina Hirschi Wyss wrote:
>> Hello,
>>
>> I'm preparing my master's thesis on the subject of handling fuzzy objects using the fuzzy logic, with the focus on geometries (not on the thematic level).
>> I wanted to know, if there has already been a discussion about implementing this in QGIS or in a plugin.
>>
>
> As far as I know, no one is working on this or has discussed it. But its
> an interesting topic and it would be nice to see some real innocation
> happening in QGIS.
>
>> Showing the uncertainty of boundaries is needed in some cases of spatial planning, when the "crisp" geometries are not yet defined.
>>
>> A possible use case could also be to draw a polygon with certain attributes, then the border of the polygon "copied" to one or more oriented polyline layers with special attributes (e. g. the distance of the uncertainty, to which the fuzzy-function is applied). These polylines are linked by a foreign key to the polygon-feature. This would certainly require the use of a database, namely Postgre/PostGIS.
>> A polyline layer (linked to the polygon) can also be "crisp" e.g. if the border is a street or a river. So it should be possible to combine crisp and fuzzy segments for the same polygon.
>> Visualising this could result in a polygon with a sort of "thick pen-trace"  (the thickness corresponding to the distance-attribute of the polyline) boundary, showing the uncertain band. The thickness corresponds to the distance-attribute of the polyline.
>>
>> Another possible visualisation (sort of fuzzy buffers) is presented in the following paper: http://www.geo3.nl/12%20fuzzy%20set%20theory.pdf (fig. 1b).
>>
>
> Right - one could probably apply blur effects and similar to lines to
> represent their fuzzyness - Qt4 already has some infrastructure for this
> kind of thing e.g.
> http://doc.qt.nokia.com/4.6/qgraphicsdropshadoweffect.html#details
>
> I'm not sure about using two separate layers as you describe above - it
> might be nicer to make fuzziness simply an attribute of the feature -
> though I guess it doesnt cope well for the scenario where individual
> segments of a feature have different fuzziness levels...
>
>
>> If there are developers interested in this, I would be glad to know, as my own programming skills are rather basic.
>
>
> Look forward to seeing your proof of concepts!
>
> Regards
>
> Tim
>
>>
>> Thanks in advance
>> Annina_______________________________________________
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>
>
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