[vtkusers] Frustum Culling

[Michael Knopke]

Problem is, that I can’t use the latest cvs for my app, coz it has several
issues. Lately I can’t even start the app, gives me strange access
violations in vtkPlane.cxx (even though this is the same file I use).
I tried installing only vtkExtractSelectedFrustum but there where too many
dependencies.
I read the source code and can’t really say how they detect the
vtkInsideness, it’s a different way than what I tried, maybe I try to adopt
the code.
 
Another Question: I read that data inside the frustum will be tagget with
the attribute “vtkInsideness” How can I querry a Dataset for this attribute?
 
Regards
 
Michael
 
 
 
 
 
 
>Have you tried vtkExtractSelectedFrustum?
 
On 3/6/07, Michael Knopke <Michael.Knopke at gmx.de
<http://www.vtk.org/mailman/listinfo/vtkusers> > wrote:
> 
>  Hi,
> 
> 
> 
> I'm trying to write a new vtk-filter that can crop-out (set scalars to
> fixed value e.g. 0) selected volumes (e.g. inside of BoxWidget).
> 
> Unlike all other cropping filter I know, will this filter work with
> vtkImageData and preserve topology and geometry. This means it will not
cut
> cells.
> 
> Therefore I'm trying to implement frustum culling (with the planes from
> BoxWidget) and later add octree to speed up calculation.
> 
> 
> 
> The problem I have is regarding detection if the point that is evaluated
> lies behind the plane. As far as I know, one has to calculate:
> 
> 
> 
> 1). Shortest distance to plane (this works well)  à returns
> PlanePointDistance
> 
> 
> 
> 2). Add this distance to the DotProduct of ( PointX, NormalOfPlane):
> 
> 
> 
>    Result = PlanePointDistance + (vtkMath::Dot(PointX, Normal));
> 
> 
> 
> 3). If result is negative than pointX lies behind Plane
> 
> 
> 
> 
> 
> Unfortunately this yields wrong results. Does anybody know what's wrong?
> 
> 
> 
> Michael

 

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