Tr: how to compute central line form surface objects

[Tim Hutton]

At 15:58 21/02/00 +0100, you wrote:
>     ----- Original Message -----  
>From: Olivier  Coulon  
>To: Jan Ehrhardt 
>Cc: vtk users  
>Sent: Monday, February 21, 2000 2:28 PM 
>Subject: Re: how to compute central line form surface  objects 
>Jan Ehrhardt wrote:  
> I have surface objects of anatomical tube-like structures (e.g. vessels) 
> How can I compute a central line (the skelett) of a surface object ?    
> Thanks.            
> Jan
> 
>Jan,  I think it is not a very simple problem. If your structure is a
>vessel, I  guess orthogonal sections are not exact circles and they are not
>even exact  ellipses. 

But if the cross-sections are approximately ellipses then you could use an
ellipse-fitting routine. Use the polygon normals to get at the plane of
cross section for the tube, then find the ring of points that intersect
this plane. (Bit tricky, might have to reject distant intersections.) Then
simply run a robust ellipse-fitting routine over the set of points and
extract the center of the ellipse to give you the skeleton point. Repeat
this along the tubes to build your central line.

Code for ellipse-fitting attached, all credit to Maurizio Pilu et al. Will
have to adapt to your purposes, it is set up to draw into a Microsoft
Visual C++ MFC drawing context.

Hope this helps, it is not an easy problem.

Cheers,

Tim.

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Tim Hutton, Research Assistant            Email: T.Hutton at eastman.ucl.ac.uk
MINORI Project                          Eternal: T.Hutton at excite.co.uk
Dental and Medical Informatics     http://www.eastman.ucl.ac.uk/~dmi/MINORI
          
Eastman Dental Institute, UCL                    Tel: [+44] (0207) 915 2344
256 Gray's Inn Road, London WC1X 8LD, UK         Fax: [+44] (0207) 915 2303
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