[Qgis-developer] Approximation and geoprocessing

Bernhard Ströbl bernhard.stroebl at jena.de
Mon Jan 13 22:39:10 PST 2014

Hi Paolo,

agreed, that eliminate does not solve the "mouse-tail" problem. It aims 
at getting rid of sliver polygons resulting from processing input layers 
having been digitized on different maps or scales.


Am 13.01.2014 17:58, schrieb Paolo Cavallini:
> Il 13/01/2014 09:12, Bernhard Ströbl ha scritto:
>> it depends...
>> Processing works as follows: take input layer(s) - do a process - create output layer
>> So if the "process" is a selection the result is an output layer with only the
>> selected features included.
>> Therefore for "eliminate" I included a simple logical selection based on a field in
>> the layer. Thus to use eliminate in a model you first have to create an input layer
>> with a field that somehow marks all features to be eliminated (e.g. caluclate
>> area/perimeter). Currently I do not know how this can be achieved. :-(
>> Any hints welcome.
> IMHO the approach should be different: eliminating features a posteriori is always
> feasible, but very inefficient, and it does not solve the "mouse tail" problem: a
> valid feature is created, but attached to it hangs a close-to-zero-area that results
> from different approximation of coordinate values.
> This may seem a corner case, but is indeed preventing effective analyses in real cases.
> All the best.

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