[postgis-users] non-convex or concave hull

[Andreas Neumann]

Hi all,

I am looking for a method that generates me an enclosing polygon that
should contain all input geometries but is not as big as the polygon
generated by the ST_ConvexHull() command. The input should be a list of
different geometries (point,linestring,polygon), and the output should be
one polygon that can contain concave outlines but needs to guarantee that
all input geometries are inside. I don't know if any term exists for such
a polygon. Concave-hull? Non-convex hull?

Googling around I came across:

http://www.spatialanalysisonline.com/output/html/Non-convexhulls.html

>From the figure, version "d" is actually what I want as a result. Or here
is another pointer:
http://ubicomp.algoritmi.uminho.pt/local/concavehull.html

My question now: Are there existing methods in Postgis or geos that would
help me generate such polygons? If not - how many hours would a Postgis
programmer potentially need to implement such an algorithm in Postgis?

Thanks,
Andreas

-- 
Andreas Neumann
http://www.carto.net/neumann/
http://www.svgopen.org/