[OSGeo-Discuss] open source polygon cluster aggregation algorithm?

[Stefan Steiniger]

how about using R it has alpha shapes and a-like?

What you describe sounds like a problem in map generalization. I.e. the 
approach of buffering is something what a colleague of mine once 
implemented to generalize house-blocks for maps (aggregate the single 
buildings). Unfortunately I don't know of any accessible code for that.

If you are proficient in Java or C++ you could make you custom 
implementation with JTS or Geos (sounds easy to me).

on what geographic objects are you working on? and how much does the 
shape to be need to maintained?

stefan

G. Allegri wrote:
> <Aside>
> A nice implementation of alpha shapes with jts:
> http://www.mail-archive.com/jts-devel@lists.jump-project.org/msg01019.html
> </Aside>
> 
> 2010/5/6 G. Allegri <giohappy at gmail.com>:
>> Thanks Andrea for the links. Yes, I think the problem is similar, in
>> fact I was also looking for concave hull and alpha shapes algoithms,
>> but the only open solution I've found is from CGAL [1] and... it's too
>> complex to extract and reimplement in my context (database procedural
>> programming).
>>
>> IWe have implemented something very "rude":
>>
>> 1 - logically aggregate polyongs in clusters (given a certain distance)
>> 2 - buffer each polygon mantaining the shape (not the usual buffer,
>> which make rounded artifacts)
>> 3 - geometrical union
>> 4 - shrink the result (unbuffer)
>>
>> But I have the time for a long holiday waiting the end of the process :)
>>
>> [1] http://www.cgal.org/Manual/last/doc_html/cgal_manual/Alpha_shapes_2/Chapter_main.html
>>
>> 2010/5/6 Andrea Aime <aaime at opengeo.org>:
>>> G. Allegri ha scritto:
>>>> I'm looking for an algorithm to do polygon cluster aggregation,
>>>> similar to the ArcInfo "Aggregate Polygon" [1].
>>>> I know about GEOS "Cascaded Union", but I need two more features:
>>>>
>>>> 1 - clustering of polygons that fall within a a certain threshold
>>>> distance from each other
>>>> 2 - mantain orthogonality, i.e. the original angles/shapes
>>> I don't know of any such implementation, but it looks somewhat
>>> similar to the computation of a concave hull:
>>>
>>> http://ubicomp.algoritmi.uminho.pt/local/concavehull.html
>>> http://stackoverflow.com/questions/83593/is-there-an-efficient-algorithm-to-generate-a-2d-concave-hull
>>>
>>> Cheers
>>> Andrea
>>>
>>> --
>>> Andrea Aime
>>> OpenGeo - http://opengeo.org
>>> Expert service straight from the developers.
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