[vtkusers] Cool sample does not work, need help !!

[de Boer Ingo]

Hi,

I tried the frustum planes. But it still does not work for
perspective projection, only for parallel projection.
Did I do anything wrong in my programming, did I miss something ?

Any further hints on this sample ? This new sample uses the
frustum planes...


greets
  Ingo

---
Dr.-Ing. Ingo H. de Boer

Polytec GmbH
Polytec-Platz 1-7, 76337 Waldbronn, Germany
phone: ++49 7243 604 106
fax  : ++49 7243 604 255
 

> -----Original Message-----
> From: Andrew Maclean [mailto:a.maclean at cas.edu.au]
> Sent: Wednesday, September 15, 2004 1:00 AM
> To: de Boer Ingo; vtkusers at vtk.org
> Subject: RE: [vtkusers] Cool sample does not work, need help !!
> 
> 
> It is definitely a cool sample!
> 
> As you indicate, what you have written works perfectly well 
> for parallel
> projections. If you look at DisplayToWorld() in your code, there is no
> perspective transform being applied to the coordinates, so Pt4[3] will
> always be 1. You are simply taking the viewport coordinates 
> and converting
> them to world coordinates. This is fine for parallel 
> projections but not for
> perspective projections.
> 
> For perspective projections, you actually need the view 
> frustum and you can
> get the planes bounding this from 
> vtkCamera::GetFrustrumPlanes(), remember
> :- the "aspect" is the width/height of the viewport. My 
> initial approach
> would be to construct a frustum from these planes and use the 
> edges of the
> nearest face as your bounding rectangle. This will also work 
> for parallel
> projections, however the frustum will simply become a cube in 
> this case.
> 
> An alternative approach may be to use vtkCamera::
> GetPerspectiveTransformMatrix() and 
> vtkCamera::GetViewTransformMatrix() to
> directly map the viewport bounds to word coordinates. However 
> I think that
> using vtkCamera::GetFrustrumPlanes() will be a better approach.
> 
> 
> Let me know how this works. We (the users group) would love 
> to see the final
> result!
> 
> 
> Regards,
>    Andrew
> 
> ___________________________________________
> Andrew J. P. Maclean
> Centre for Autonomous Systems
> The Rose Street Building J04
> The University of Sydney  2006  NSW
> AUSTRALIA
> Ph: +61 2 9351 3283
> Fax: +61 2 9351 7474
> URL: http://www.cas.edu.au/
> ___________________________________________
> 
> 
> 
> 
> 
> -----Original Message-----
> From: de Boer Ingo [mailto:I.deBoer at polytec.de] 
> Sent: Friday, 10 September 2004 21:18
> To: vtkusers at vtk.org
> Cc: vidyadhar at lucidindia.net
> Subject: [vtkusers] Cool sample does not work, need help !!
> 
> Hi all,
> 
> Vidyadhar and I are working on this cool zoom sample.
> We have a cube in a large and small renderer. Now, when
> you zoom into the large renderer, you see a red rectangle
> in the small renderer to show you the zoomed ROI from
> the large renderer... well... play with it, you'll get it ;)
> 
> There is still a problem :(
> 
> The sample only works okay in parallel projection. The
> perspective projection does not work !!
> 
> So, this goes out to all the VTK gurus to take a look at
> this. This sample could also be a nice one for the VTK CVS
> and very usefull to some other users.
> 
> You can toogle the perspective/parallel with the line
> 
> #define _WORKING_SAMPLE_
> 
> 
> greets
>   Ingo
> 
> 
> ---
> Dr.-Ing. Ingo H. de Boer
> 
> Polytec GmbH
> Polytec-Platz 1-7, 76337 Waldbronn, Germany
> phone: ++49 7243 604 106
> fax  : ++49 7243 604 255
> 
> 
> 
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