[vtkusers] projections and transformations

[David Doria]

> 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?

Thanks,

David