Re: Concave hull 3D

Posted by Eddie Iannuccelli on Aug 09, 2007; 10:55am
URL: http://imagej.273.s1.nabble.com/Concave-hull-3D-tp3698649p3698653.html

I agree with you but I was wondering if the problem coud be solved by
using some "biological" constraints on angles and distances between 2
surface points. My objects are always more continous and curved than
your cube example, concave regions are generally made by several points
in a progressive curve so this kind of ambiguous case are not so much
encountered. I know some plugins can get isosurface from an imagestack.
Could that isosurface approach resolve my problem ?

Regards

Johannes Schindelin a écrit :

> Hi,
>
> On Thu, 9 Aug 2007, Eddie Iannuccelli wrote:
>
>  
>> I am currently using QuickHull3D java lib to build a 3D shape from a surface
>> Point3f list. My biological objects (cell nucleus) are not always convex and
>> QuickHull3D always returns convex shapes so now  I am looking for a way to
>> produce concave 3D shapes from surface points (no image available, only
>> surface points list).
>>    
>
> This is not a well defined problem.  Imagine a cube.  Put points onto all
> 8 of its corners.  Now put a 9th point into its center.
>
> The convex hull is well defined.  But what should a concave hull do?
>
> Should it produce the cube? (Volume 1 for dimensions 1x1x1)
>
> Or should it produce a cube with one "dent", i.e. replace one side by the
> four triangles built by the four corners and the cube's center?  (Volume
> 5/6 for dimensions 1x1x1)
>
> Or should it just produce the triangles built by any two adjacent corners
> and the cube's center (Volume 0 for any dimension)?
>
> It is highly ambiguous.
>
> Ciao,
> Dscho
>
>  

--
******************************************
Eddie Iannuccelli
Laboratoire de génétique cellulaire
INRA - Castanet Tolosan
Tel: [phone] / Fax: [phone]