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

[Mike Toews]

The recent JTS has a nice buffering options, namely the mitre buffer.
It does not have rounded corners, and has been very useful to me
(i.e., we can physically survey-out the buffer on the ground with
fewer points to locate and stake out).
http://lin-ear-th-inking.blogspot.com/2007/12/new-buffer-styles-in-jts-19.html

Although I'm no expert at plsql, it appears it can be extended with
java, so maybe it could be possible to wrap the Oracle WKT/B(?)
through JTS:
http://www.devshed.com/c/a/Oracle/Extending-PLSQL-with-Java-Libraries/

Someone must have done this for plsql in the past ...

-Mike

On 9 May 2010 06:01, G. Allegri <giohappy at gmail.com> wrote:
> Hi Stefan. You guessed right, it's buildings generalization. I know
> jts and geos quite well but unfortunatly I  can't use them because I'm
> working directly on oracle with plsql. I think buffer is the way, but
> not the one oracle provides because it rounds the corners...
>
> Bye,
> Giovanni
>
> 2010/5/7 Stefan Steiniger <sstein at geo.uzh.ch>:
>> 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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