[vtkusers] EyePosition / EyeTransform, GPU Volume Rendering, and Off-Axis Projection

[Krzysztof Kamieniecki]

I have a patch available (i'm not sure where to send it). I changed
vtkCamera and vtkOpenGLGPUVolumeRayCastMapper to produce and expect
GetEyePosition() to give the actual eye position in world space. This seems
to fix my problem. I think there may still be a clipping issue because of
the use of GetEyePlaneNormal in vtkRenderer. I have to fix some of my own
code to get more testing done and I would like to hear more about the
original intent of EyePosition before making any more changes.

On Fri, Jul 6, 2012 at 1:54 PM, Krzysztof Kamieniecki
<krys at kamieniecki.com>wrote:

> Hi Aashish,
>
> I would like to try to take a stab at it.
>
> Based on the only use of GetEyePosition in VTK it seems like
> GetEyePosition should return the world space positions. (This expectation
> also explains the problems I have been seeing with weird clipping)
>
> from vtkRenderer::ResetCameraClippingRange
> ...
>   if(!this->ActiveCamera->GetUseOffAxisProjection())
>     {
>     this->ActiveCamera->GetViewPlaneNormal(vn);
>     this->ActiveCamera->GetPosition(position);
>     this->ExpandBounds(bounds,
> this->ActiveCamera->GetModelTransformMatrix());
>     }
>   else
>     {
>     this->ActiveCamera->GetEyePosition(position);
>     this->ActiveCamera->GetEyePlaneNormal(vn);
>     this->ExpandBounds(bounds,
> this->ActiveCamera->GetModelViewTransformMatrix());
>     }
> ...
>
> My current understanding is that the OffAxisProjection perspective
> transformation matrix is being used by the GPU Renderer to setup to outer
> polygons.
>
> So the main thing to do would be to produce world coordinate Eye Positions
> and use those instead of the Camera Position in the volume Renderer, so the
> shaders would get the proper ray directions?
>
> What is the desired functionality of EyeTransform? WorldToEye, EyeToWorld,
> CameraToEye, EyeToCamera?
>
> Best Regards,
> Krys
>
> On Fri, Jul 6, 2012 at 1:41 PM, Aashish Chaudhary <
> aashish.chaudhary at kitware.com> wrote:
>
>> Hi Krzysztof,
>>
>> On Fri, Jul 6, 2012 at 1:12 PM, Krzysztof Kamieniecki
>> <krys at kamieniecki.com> wrote:
>> > Hi,
>> >
>> > How is the EyePosition and EyeTransform functionality supposed to
>> behave,
>> > should the positions be in CameraSpace or WorldSpace?
>> >
>> > Should they be syncronized with EyeSeparation / LeftEye when in Off-Axis
>> > Projection mode?
>>
>> >
>> > I am trying to get the GPU Volume renderer to work with Stereo 3D in
>> > Off-Axis projection mode, one problem seems to be that the Camera
>> position
>> > is used instead of the Eye position.
>>
>> This is a known problem and based on my prior discussions with volume
>> rendering experts here at Kitware, I believe that this needs to be
>> fixed on the volume rendering side of things.
>> If you want to make it work by yourself then we could provide you
>> guidance for this task.
>>
>> Thanks,
>>
>>
>>
>> >
>> > Thanks,
>> > Krys
>> >
>> > _______________________________________________
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>>
>>
>> --
>> | Aashish Chaudhary
>> | R&D Engineer
>> | Kitware Inc.
>> | www.kitware.com
>>
>
>
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