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/[email protected]/msg01019.html
</Aside>
2010/5/6 G. Allegri <[email protected]>:
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 <[email protected]>:
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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