> Hi Eddie,
>
> Googling for "concave hull" there is quite a bit of information about
> this idea. One informative writeup is here:
>
http://ubicomp.algoritmi.uminho.pt/local/concavehull.html>
> It appears that the algorithm essentially works based on density and
> proximity. Unfortunately the link to the online version of their
> algorithm seems nonfunctional, but you could try emailing them. It is
> probably worth starting from some existing code, as this problem is
> certainly nontrivial.
>
> -Curtis
>
> On 8/9/07, Eddie Iannuccelli <
[hidden email]> wrote:
>
>> 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: 05 61 28 54 44 / Fax: 05 61 28 53 08
>>
>>