[vtkusers] projections and transformations

[David Gobbi]

If you use vtkPerspectiveTransform, the points will be divided by the
homogeneous coordinate automatically.  If you use a vanilla
vtkTransform, then there is no division.

   David G.


On Tue, Feb 16, 2010 at 2:55 AM, Giancarlo Amati
<ilferraresebono at hotmail.it> wrote:
> Good morning Guys,
>
> this is my question:
>
> I have a dataset, and a projection matrix resulting from a calibration
> process. now:
>
> the projection matrix P = 3x4 matrix. While transformation in VTK are 4x4
> matrices.
> So, I transformed my P in a 4x4 by inserting a NULL row inbetween the 2nd
> and the 3rd row. this makes  the Z null.
>
> Now If I put this final P into a vtkTransform object and apply to my
> polydata, are the coordinates in the politdata divided automatically by that
> famous homogeneous coordinate factor W?
>
> let's say that PD is my PolyData and I want to visualized the 2D by multiply
> P * PD where of course I get coordinate like (Xi,Yi, 0, Wi). But now I would
> like Xi/Wi which is a homogeneous normalization.... is it that automatic or
> I have to make it expiciltly?
>
> Very kind regards.
> Giancarlo
>
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