[postgis-devel] [PostGIS] #312: ST_ConcaveHull

[PostGIS]

#312: ST_ConcaveHull
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 Reporter:  robe         |       Owner:  robe         
     Type:  enhancement  |      Status:  assigned     
 Priority:  medium       |   Milestone:  PostGIS 2.0.0
Component:  postgis      |     Version:               
 Keywords:               |  
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Comment(by robe):

 Thought about calling it alpha hull, but didn't much like that term.  The
 algorithms we used I couldn't really think of how it mapped to all those
 discussed in the literature.

 The basic inspiration of it comes from a dream where you start with a
 Convex Hull and then you cave it (shrink wrap) in until you can cave it in
 no more.  The percent target is meant to be the percent target of the
 convex hull.  Well in theory if you think about it, you can't always hit
 your target percent and sometimes it even overshoots depending on how it
 slices up the geometry.  So the function recurses trying to reach the
 target until it reaches a point where it can do no better (or hits one of
 those topological exceptions thrown by GEOS) and then exits with the best
 solution it had.

 Right now we're tackling issues with GEOS with the tolerances causing
 problems and yielding too many  topological exception errors (and fixing
 sometimes produces a concave hull that does not fully contain the
 geometry). Haven't revisited that yet
 -- but will soon once other tasks lighten up.

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/312#comment:6>
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