AW: [vtkusers] triangulation from surface points?

[Tim Hutton]

Zein,

Have a look at vtkRuledSurfaceFilter. The points in each plane should join 
up to form a closed line, at least if your object is closed and contiguous. 
Then these lines can be combined to form a surface using this filter.

Alternatively, consider that your points actually define a binary volume 
(-1 inside, 1 outside) since you have points and normals. Thus there are 
(at least) two approaches:

1. create a volume, and go through each voxel inserting:
       1 if the nearest surface point's normal is pointing towards the voxel
       -1 if the normal points away
    then use vtkContourFilter (contours at 0 by default) to get a polygonal 
surface

OR

2. for each plane, compute a binary image using a polygon painting 
algorithm (think this can be done in VTK now) and stack these images up to 
form a volume. Then use vtkContourFilter as before.

All of these approaches need familiarity with VTK, which takes a while to 
learn but is worth it if you plan to tackle similar problems in the future!

As another alternative, there are lots of packages out there that do this 
kind of thing. (NUAGES springs to mind but this may be old and gone now). 
And if you can get hold of the volume data from which your points came in 
the first place then you will save yourself a lot of work.

Tim.

At 18:31 06/10/2003 +0200, salah wrote:
>Thanks Tim,
>
>I am actually a newby to vtk!
>
>my data points are structured in planes, and have normals.
>How can I make use of this? How can this help making a choice?
>
>Many thanks and greatings,
>
>Zein
>
> > -----Ursprüngliche Nachricht-----
> > Von: Tim Hutton [mailto:T.Hutton at eastman.ucl.ac.uk]
> > Gesendet: Montag, 6. Oktober 2003 18:27
> > An: salah; ITK Users (E-Mail); VTK Users (E-Mail)
> > Betreff: Re: [vtkusers] triangulation from surface points?
> >
> >
> > Hi Zein,
> >
> > There are a few options in VTK. I'm not so familiar with ITK.
> >
> > 1. If your surface is convex then vtkDelaunay3D plus
> > vtkGeometryFilter is
> > your friend.
> >
> > 2. If your data points are structured in any way (eg. in
> > planes, or in
> > stripes) then you need to take full advantage of this to get the best
> > results. Likewise if your points have normals.
> >
> > 3. If your sample points really are randomly sampled on the
> > surface then
> > you can try: vtkSurfaceReconstructionFilter (caveat: only
> > works on nice
> > clean closed data, and only sometimes) or
> > vtkPowerCrustSurfaceReconstruction
> > (http://www.eastman.ucl.ac.uk/~thutton/powercrust/) which
> > works much better
> > but isn't part of VTK.
> >
> > 4. Use an external program to reconstruct the surface and import the
> > results into VTK.
> >
> > In general this is quite a hard problem, so good luck!
> >
> > Tim
> >
> > Also this is quite a common question, so a search of the mailing list
> > archives may have helped.
> >
> > At 17:57 06/10/2003 +0200, salah wrote:
> > >Hello all,
> > >
> > >I have a set of points sampled at the surface of a closed
> > >object. I want to generate a triangulation from them. In
> > >other words, I want to generate a mech describing the
> > >surface.
> > >Is there some filter in vtk/itk  that does something like this?
> > >
> > >Thanks in advance,
> > >
> > >Zein
> > >_______________________________________________
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> > --------------------------------------------------------------
> > -------------
> > Tim Hutton,
>http://www.eastman.ucl.ac.uk/~thutton
>Research Fellow & PhD student,                   T.Hutton at eastman.ucl.ac.uk
>MINORI Project, Biomedical Informatics Unit,
>Eastman Dental Institute, UCL,                   Tel: [+44] (0)20 7915 2344
>256 Gray's Inn Road, London WC1X 8LD, UK         Fax: on request
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