[vtkusers] Outer surface

[John Biddiscombe]

NB. This assumes closed surfaces. If the surfaces aren't closed, it's not
obvious what's in and wha'ts out.

----- Original Message ----- 
From: "John Biddiscombe" <john.biddiscombe at mirada-solutions.com>
To: "Perrine PAUL" <perrine.paul at chu-rennes.fr>; <vtkusers at vtk.org>
Sent: Friday, January 30, 2004 12:17 PM
Subject: RE: [vtkusers] Outer surface


For each cell in polydata
  Find cell normal
  Fire ray from point (cell centre + epsilon*normal) to {x,y,+infinity}
  Count number of itersections of ray along path
  if number odd. Cell interior - kill it
  if number even (or zero), cell on surface. Keep it
End loop
(For best results, do three rays, in +x, +y, +z directions to minimize
chance of ray passinng through crack between edges of polygons, use
tolerance carefully).

Use vtkCellLocator + IntersectWith line + some custom checks to get all
intersections instead of just first one.

JB



> -----Original Message-----
> From: vtkusers-admin at vtk.org [mailto:vtkusers-admin at vtk.org]
> On Behalf Of Perrine PAUL
> Sent: 29 January 2004 16:36
> To: vtkusers at vtk.org
> Subject: [vtkusers] Outer surface
>
>
> Hello everyone,
> I have a  skull surface (in VTK format) segmented from a CT
> scan. The problem is: since the skull has a thickness, my
> surface is composed of 2 connected surfaces, I call them the
> outer and the inner surfaces. I would like to build a new
> polydata with only the outer surface. Do you have any idea
> about how do that? Cheers, Perrine
>
> -- 
> Perrine PAUL - PHD Student
> +33 2 23 23 49 91
> Laboratoire IDM, http://idm.univ-rennes1.fr
> Université de Rennes 1, Faculté de médecine
>
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