[vtkusers] implicit function from polydata

[Frederic DANESI]

Hi,

I am sure to follow your method here ...
Usually, when you want to know if a point is inside a closed surface, you
shoot a ray and count the intersection ...

If you want to do so, or find out what others have done, you may find some
useful hints in the work of Dave Pont (see VTK users archives) and here :
http://staff.science.uva.nl/~dshamoni/myprojects/Boolean.html

Regarding your code: since you have projected the polydata on the z-plane,
you should use vtkDelaunay2D instead of Delaunay3D.  Be aware however that
you will get only a convex hull if you do not have to outer edges to provide
vtkDelaunay with ...

HTH
Fred.


2011/3/25 vlibertiaux <vlibertiaux at gmail.com>

> Hi everyone,
>
> I am trying to create an implicit function from a polydata using
> ImplicitDataSet.  My final goal is to determine if a given point lies
> within
> a volume described by its outer surface.
>
> I tried it two different ways: first I created an ImplicitDataSet directly
> from my polydata using this code:
>
> vtkElevationFilter *efilter = vtkElevationFilter::New();
> efilter->SetInput(polydata);
> efilter->Update();
> vtkImplicitDataSet *dataset = vtkImplicitDataSet::New();
> dataset->SetDataSet(efilter->GetOutput())
>  then when I test if a point "belongs" to this function with
> dataset->FunctionValue(x,y,z) <= 0 , none of them seems to verify the
> condition.
>
> I then tried another approach: I do a projection of my polydata to the
> z-plane, and define a new polydata which is flat (contour).
>
> I then use this piece of code to create the implicit data set :
>
> vtkDelaunay3D *delaunay = vtkDelaunay3D::New();
> delaunay->SetInput(contour);
> delaunay->BoundTriangulationOff();
> delaunay->Update();
> vtkElevationFilter *efilter = vtkElevationFilter::New();
> efilter->SetInputConnection(delaunay->GetOutputPort());
> efilter->Update();
> vtkImplicitDataSet *dataset = vtkImplicitDataSet::New();
> dataset->SetDataSet(efilter->GetOutput())
> dataset->SetOutValue(-1000000);
>
> and I test with :
>
> dataset->FunctionValue(x,y,0) != -1000000
>
> In either case, the condition is not verify but I know that some points
> verify them.
>
> Any help will be greatly appreciated !
>
> Thank you very much,
>
> V.
>
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-- 


Cordialement,
F.Danesi
-- 
Responsable Développement Informatique et Travail Collaboratif
Centre Technique DINCCS (Centre Technique Dédié à l’Ingénierie Numérique, la
Conception Collaborative et la Simulation)
MICADO / DINCCS
Pôle de Haute Technologie, BP 90005
08005 Charleville-Mézières Cedex
Tel. : +33 (0) 3.24.41.69.55 / +33 (0) 6.62.76.13.32
Email : frederic.danesi at dinccs.com
Web : www.afmicado.com / www.dinccs.com

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