[vtkusers] vtkFixedPointVolumeRayCastMapper related help

[Randall Hand]

Unfortunately, you can't stack multiple volumes like that.  The way that
those mappers work is to essentially render the image in software
(offscreen), then display the result.. There's no depth, it's just a 2d
image.. The intermix is for mixing 2d Geometry with 3d volume-renderings,
but won't work with multiple volume renderings.

If your 3 volumes are from the same data, or you can make the 3 datasets
coincident (interpolation, resampling, whatever) then you can put all of the
variables into a single multi-value field array, and independently map a
different colormap onto each variable.  For an example, look on the Back
Cover of the Fall2007 EnVision magazine (available here:
https://visualization.hpc.mil/wiki/EnVision ).  I generated those images
with the FixedPointVolumeRayCastMapper with 2 separate colormaps, one
red/yellow and one green/blue, each mapped onto a separate component of a
vector field where field[0] = Kinetic Dissapation and field[1] = Thermal
Dissapation.

On Jan 7, 2008 7:04 PM, Alark Joshi <alark_j at hotmail.com> wrote:

>
> Hello,
>
> I have three volumes that are all located in the same space and I would
> like to see regions where they overlap and so on.
>
> On trying to using raycastMapper/texture2d/texture3d, I found that the
> last vtkVolume that I added to the renderer always dominated the
> visualization. Basically, if I order the volumes as
>
> ren->AddVolume(v1);
> ren->AddVolume(v2);
> ren->AddVolume(v3);
>
> then volume v3, dominates the visualizations and occludes everything
> behind it. I tried this with the "nut.slc" and "bolt.slc" too, in my
> earlier attempts. Then I found  "vtkFixedPointVolumeRayCastMapper" that
> allows, as per the specification "intermixing with geometric data".
>
> I was able to get one volume and one actor (in the example of the nut and
> bolt), to work perfectly. But, it does not work as well with my real world
> data, since I need the actor to be translucent. As soon as I change the
> opacity of the actor, the volume again dominates the visualization and the
> 3-dimensionality is lost.
>
> Ideally, I would like to be able to render all these 3 volumes and I have
> a feeling that vtkFixedPointVolumeRayCastMapper has the answer and I may not
> be using it properly. The class specification mentions "It works with all
> input data types and up to four components."
>
> Please let me know if anyone has any suggestions/ideas. Thanks.
>
> Regards,
>
> Alark_______________________________________________
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-- 
----------------------------------------
Randall Hand
Visualization Scientist
ERDC MSRC-ITL
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