[vtkusers] projections and transformations

[Giancarlo Amati]

WOW guys! thank you very much for all the suggestions about this topic.
You helped me a lot...and I hope this works soon.....
Many thanks!
Giancarlo

> From: david.gobbi at gmail.com
> Date: Tue, 16 Feb 2010 07:12:15 -0700
> To: daviddoria+vtk at gmail.com
> CC: vtkusers at vtk.org
> Subject: Re: [vtkusers] projections and transformations
> 
> On Tue, Feb 16, 2010 at 6:56 AM, David Doria <daviddoria+vtk at gmail.com> wrote:
> >> It divides by the "w" coordinate, which is the 4th: (x, y, z, w).
> >> When you call TransformPoint(x,y,z) it creates a homogeneous
> >> coordinate (x,y,z,w) with w=1, and then multiplies it by the 4x4
> >> matrix.  Then it returns (x/w, y/w, z/w).
> >>
> >>   David G
> >>
> >
> > Ah right, again because it is a 4x4 projection matrix. What do you
> > think about adding vtkMatrix3x4 for typical "P = [KR | -KRC]" camera
> > projection matrices?
> 
> The 4x4 matrix is the basis for the VTK transforms, so a vtkMatrix3x4
> would have to be converted to a vtkMatrix4x4 before it could be used.
> My opinion is that a 3x4 matrix would be kind of useless.  A person
> can just construct a 4x4 matrix that does the same thing.
> 
>   David G
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