[vtk-developers] BestFitPlane function for vtkPlane

[Karthik Krishnan]

Thanks

On Wed, Nov 4, 2009 at 11:36 AM, David Doria
<daviddoria+vtk at gmail.com<daviddoria%2Bvtk at gmail.com>
> wrote:

> On Wed, Nov 4, 2009 at 11:28 AM, Karthik Krishnan
> <karthik.krishnan at kitware.com> wrote:
> > On Wed, Nov 4, 2009 at 10:33 AM, David Doria <daviddoria+vtk at gmail.com<daviddoria%2Bvtk at gmail.com>
> >
> > wrote:
> >>
> >> On Wed, Nov 4, 2009 at 8:28 AM, Karthik Krishnan
> >> <karthik.krishnan at kitware.com> wrote:
> >> > Add a third redundancy to it :-). vtkDelaunay2D.
> >>
> >> I have some questions about
> >>  void vtkTextureMapToPlane::ComputeNormal(vtkDataSet *output)
> >>
> >
> > David:
> >
> > Thanks for taking the time to look at this class.
> >
> >>
> >> 1) why is the input called 'output'? The only thing the function does
> >> is set this-Normal, right? 'output' is not modified as far as I can
> >> tell.
> >
> >
> > Doesn't matter whether you call call ComputeNormal(output) or
> > ComputeNormal(input). The filters starts off by copying the geometry and
> > topology from the input to the output. See line 80 :
> >
> >     output->CopyStructure( input );
> >
> >
> >
> >>
> >> 2) the last line is
> >> this->Normal[2] = -1.0; // because of the formulation
> >>
> >> My normal computation will certainly not always have the z component
> >> of the normal = -1... why is this supposed to be the case?
> >
> > I don't think that is meant to imply that the normal vector is [0, 0,
> -1].
> > It means that the solution to the normal is the 3 component tuple after
> > solving the linear system by kramer's rule :
> >   [A, B, -1]
> >
> > The actual normal is obtained by normalizing this vector to unit norm.
> That
> > would automatically give you the solution to the z component, which need
> not
> > be -1.
> >
> > thx
> > --
> > karthik
> >
> >
> >
>
> Of course it doesn't matter what you call it - but it DOES make it
> more confusing :)
>
> About the -1, I didn't see the normalization taking place inside this
> function so I was confused, but it doesn't sound like there would be
> any problem. I have updated both of these classes but some of my
> (non-related) tests are freezing. (see my post on the users list).
> François is helping me looking into it - once they are working if all
> the tests that don't fail before my changes still pass I'll send the
> updated files to the list for you guys to approve.
>
> Thanks,
>
> David
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