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

[Giancarlo Amati]

yup, thanks David,

I've just found it. Silly me! I thought that the PerspectiveDivision is carried on at the visualization step ...not in the filter.
Many thanks!

GC

> From: david.gobbi at gmail.com
> Date: Wed, 17 Feb 2010 06:20:47 -0700
> Subject: Re: [vtkusers] vtkPoints ...how to work with them.
> To: ilferraresebono at hotmail.it
> CC: vtkusers at vtk.org
> 
> You can't set the bottom row to zero, because when (x, y, z, w) is
> multiplied by that matrix, it will give w = 0.  So when
> vtkPerspectiveTransform does the divide-by-w, you get a
> divide-by-zero.
> 
> Try using the following 4x4 matrix instead, and then
> vtkPerspectiveTransform will do the perspective division for you so
> that you don't have to do it yourself:
> 
> a b c d
> e f g h
> 0 0 0 0
> j i j k
> 
> The above matrix will set z=0 and set w=x*j + y*i + z*j + k.  Then
> vtkPerspectiveTransform will divide the new (x,y,z) by this "w" value
> before it returns.  I'm guessing that this is what you want.
> 
>    David
> 
> 
> On Wed, Feb 17, 2010 at 3:04 AM, Giancarlo Amati
> <ilferraresebono at hotmail.it> wrote:
> > 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
> >> >
> >> > ________________________________
> >> > Troppe caselle di posta? Gestiscile da Hotmail!
> >> > _______________________________________________
> >> > Powered by www.kitware.com
> >> >
> >> > Visit other Kitware open-source projects at
> >> > http://www.kitware.com/opensource/opensource.html
> >> >
> >> > Please keep messages on-topic and check the VTK FAQ at:
> >> > http://www.vtk.org/Wiki/VTK_FAQ
> >> >
> >> > Follow this link to subscribe/unsubscribe:
> >> > http://www.vtk.org/mailman/listinfo/vtkusers
> >> >
> >> >
> >
> > ________________________________
> > Ci sai fare con le parole? Scoprilo su Typectionary!
 		 	   		  
_________________________________________________________________
Scatta, ritocca e condividi le tue foto online. Gratis per te
http://www.windowslive.it/foto.aspx
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20100218/0450c77c/attachment.htm>