[vtk-developers] Multi-Volume RayCasting

[Steve Pieper]

Hi Stephan -

Yanling Liu of NCI did a vtk GPU ray caster that supports multiple volumes
(well, at least two) and you may want to have a look at that.

There's info, pictures, and links to the code here:

http://wiki.slicer.org/slicerWiki/index.php/Modules:VolumeRendering-Documentation-3.6

Best,
Steve

On Mon, Dec 19, 2011 at 11:27 AM, Stephan Rademacher <Radi1982 at gmx.de>wrote:

> Dear developers,
>
> I am trying to do multi-volume rendering in VTK. Specifically, I am trying
> to accomplish the following:
>
> My application does volume rendering of multiple datasets (using
> vtkVolumeRayCastMapper). Now I want to add a view showing the overlay of
> these datasets. Simply adding all the actors to a new renderer doesn't
> work, because the dataset rendered last will always have priority over the
> others. As far as I can see, I need a new kind of volume raycaster and
> volume raycast function, one that casts rays through all datasets at once
> and composits samples from all volumes at each step of the ray. I didn't
> find such a raycaster in VTK, and asking the users list didn't help.
>
> I am considering writing such a raycaster myself, but I am not sure how to
> do it. I want the separate datasets to appear exactly the same way as in
> their separate views, meaning they should have the same position and same
> transfer and opacity functions. If I move a single dataset in its view, I
> also want it to move in the overlay. This means that this new raycaster
> needs not only the datasets as input, but also needs access to the
> vtkVolumeProperty and vtkMatrix4x4 of the source dataset's actor.
>
> I don't want to hack something that is difficult to maintain and might
> break with new VTK releases, so I am looking for advice on how to best
> accomplish this.
>
> My first thought was creating a new actor, vtkMultiVolume, which can take
> multiple vtkVolumeProperties and multiple vtkMatrix4x4 for the positioning.
> These would be the ones that are also used in the separate views of the
> datasets. I'd then add the source datasets as input to my new RayCastMapper
> and would use the properties and matrices of vtkMultiVolume to raycast them.
>
> I am also unsure whether to use inheritance or not. Most methods of
> vtkVolumeRayCastMapper and related classes are not virtual, making this
> difficult. On the other hand, some classes used in conjunction with
> raycasting specifically expect a vtkVolume (not a vtkMultiVolume), like the
> gradient estimators used for shading.
>
> I would appreciate any advice anyone could give me on this.
>
> Thanks
> Stephan
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