[vtkusers] vtkPoints ...how to work with them.

[Giancarlo Amati]

Hi David,

well  my transformation matrix is aprojection matrix (3x4) but I add a 4th row which is null. So basically my matrix is:

a b c d
e f g h
j i j k
0 0 0 0

As I need to transform 3D points into my 2D image space.
now, as I need to dived X,Y by Z which  becomes a scaling factor.

So what I want to visualise is X/Z, Y/Z, 1 in (uv coordinate system). 

> From: david.gobbi at gmail.com
> Date: Tue, 16 Feb 2010 13:00:08 -0700
> Subject: Re: [vtkusers] vtkPoints ...how to work with them.
> To: ilferraresebono at hotmail.it
> CC: vtkusers at vtk.org
> 
> Show us your transform matrix.  I'd bet that when your points are
> multiplied by the matrix, the homogeneous coordinate ends up being
> zero.
> 
>    David
> 
> 
> On Tue, Feb 16, 2010 at 12:09 PM, Giancarlo Amati
> <ilferraresebono at hotmail.it> wrote:
> > Hello everybody, this is my code:
> >
> > vtkSmartPointer<vtkTransformPolyDataFilter> pdF =
> > vtkTransformPolyDataFilter::New();
> >         pdF->SetInputConnection(pdNorm->GetOutputPort());
> >         pdF->SetTransform(perspT);
> >         pdF->Update();
> >
> >
> >  vtkSmartPointer<vtkPolyData> T_persp_pd = pdF->GetOutput();
> >         T_persp_pd->Update();
> >
> >  vtkSmartPointer<vtkPoints> T_pdPoints = T_persp_pd->GetPoints();
> >         cout << "N points: " << T_persp_pd->GetNumberOfPoints();
> >
> >
> >         //Normalize the points
> >         for( int i = 0; i<T_persp_pd->GetNumberOfPoints(); i++) {
> >             double p[3];
> >             T_persp_pd->GetPoints()->GetPoint(i,p);
> >             cout<< "POints i: " << i << " " << p[0] << endl;
> >             p[0] = p[0]/p[2];
> >             p[1] = p[1]/p[2];
> >             p[2] = p[2]/p[2];
> >         }
> >
> > when I print out the 3D vector p, I always get: -1.INF0000000000 which is
> > clearly a mistake. What's the problem in my code?
> >
> > thanks a lot!
> > Giancarlo
> >
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