[Paraview] [ParaView] Off axis Projection and Stereo

[Aashish Chaudhary]

Hi Stephen.

On Thu, Nov 24, 2011 at 5:34 AM, Stephan Rogge
<Stephan.Rogge at tu-cottbus.de> wrote:
> Hello,
>
> Since I can use ParaView's cave mode in my Virtual Environment (VE), I was
> able to play a bit with its stereo capabilities and the wall configuration
> (.pvx).
>
> Before I start with my discussion, I would like to give some details off my
> configuration:
>
> * Virtual Environment
>     - two back projected walls (passive stereo)
>     - each wall is 2.6 m width  x 1.6 m high
>     - the walls creates an arrow with an angle of 112°
>     - a render PC with two NVIDIA QUADRO 5000 (one GPU per wall) is
> connected to four projectors
> * ParaView
>    - To obtain a correct un-distorted image we use the edge points (world
> coordinates) of the walls to configure the two views in the pvx-file
>    - Since we use Windows 7, I was not able to define the GPU - View
> assignment in the pvx-file
>       (it seems to be, that under Windows the flag
> 'Environment="DISPLAY=:0"' is being ignored, all views presented on the
> first display). We had to
>       modify "vtkPVSynchronizedRenderWindows", to align the views in
> respect to the MPI process id.
>    - Further code modification has been done to control the stereo
> parameters EyeSeparation and EyeAngle
>
> #############################
> ## Multiple Display Support (Win7) ##
> #############################
>
> And here I like to start my discussion. At first let's talk about the
> display configuration. I had to modify "vtkPVSynchronizedRenderWindows" to
> use
> my two walls under Windows 7. I can imaging, that this is not the best
> solution. May be some problems can appear here? Please, can some of the
> developer comment this code modification? This is the code snippet:
>
> void vtkPVSynchronizedRenderWindows::UpdateWindowLayout()
> {
>      .....
>      else if (in_cave_mode)
>        {
>        if (vtksys::SystemTools::GetEnv("PV_ICET_WINDOW_BORDERS"))
>          {
>          this->Internals->SharedRenderWindow->SetSize(400, 400);
>          }
>        else
>          {
>          this->Internals->SharedRenderWindow->SetFullScreen(1);
>
>          // These two lines here has been added
>          unsigned int id =
> vtkMultiProcessController::GetGlobalController()->GetLocalProcessId();
>          this->Internals->SharedRenderWindow->SetPosition(1920 * (id), 0);
>         }
>      }
>      .....
> }
>
> ###########################
> ## Stereo Control in Cave Mode ##
> ###########################
>
> When I visualize a small object in my ParaView Cave setup, I realized that
> the parallax between left and right image became un-natural big (it hurts).
> My opinion is, when we change the zoom we need to adjust the eye separation
> (and / or the eye angle). This can be done manually or
> automatically to yield the optimal stereoscopic impression.
> An parallel project from Aashish Chaudhary (on gitorious), address this
> problem and starts to modify the VTK api, to have some control of stereo.
> Unfortunately, after reading some parts of this source code, it looks like
> only EyeAngle can be manipulated. Furthermore  changes of that
> parameter were not considered during OffAxisProjection calculation. The
> algorithm considers only the 3D points of left and right eye and not their
> angles. Thus, changes of eyes angle does not have an effect on images
> displayed in my cave.
> I've noticed a code part were the eye angles for left and right were only
> applied, when UseOffAxisProjection is turned off. And this is not the case
> when I use ParaView with my view settings. Would it be wrong, if we modify
> the IF-condition in vtkCamera::ComputeProjectionTransform() in
> order to consider always the angle:
>
> if ( this->Stereo /*** &&!this->UseOffAxisProjection ***/)   // <-----
> Disabling the check for Off-Axis-Calculation
>    {
>    // set up a shear for stereo views
>    if ( this->LeftEye )
>      {
>      this->ProjectionTransform->Stereo( -this->EyeAngle/2,
>                                          this->Distance );
> .....


Sorry it took me some time to reply. Basically in VTK there could be
various ways to get the stereo. With in Crystal eyes stereo we have
two options now,

1. Legacy stereo
2. Off axis stereo

Second is the one added recently. In VTK camera now if you set
SetUseOffAxisStereo(1) it uses 2) for stereo calculations and hence
EyeAngle in that case is ignored.

Look at the test code here:
VTK_SRC_DIR/Rendering/Testing/Cxx/TestOffAxisStereo.cxx

You can control eye separation if you choose 2).  I have added notes
on the code about this but I will make it even more explicit.

>
> Another problem arises, when I want to adjust the eye separation. I had to
> modify a couple of VTK source code files to provide the eye separation as an
>
> proxy property and to distribute it along all mpi processes. Is it planned
> to provide this parameter globally?

We are going to work on this again very soon. We can take care of this
there then. Well the idea is that we will have a more descriptive
config file ( + UI in ParaView client) where you could specify eye
separation as well.

>
> Please, let me know, what you are thinking about my ideas.

Let me know if you have some more questions. One thing I must add is
we ran into some clipping issues in ParaView and we are hoping to
address that soon. Related to this we have paraview code out there
which is not checked in master yet.

>
> Best regards
> Stephan
>
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-- 
| Aashish Chaudhary
| R&D Engineer
| Kitware Inc.
| www.kitware.com