[vtkusers] Shadow support on volume rendering

David E DeMarle dave.demarle at kitware.com
Wed Aug 8 11:55:38 EDT 2018

On Wed, Aug 8, 2018 at 10:16 AM ianl <ilindsay at insigniamedical.co.uk> wrote:

> Hello again, apologies for (re)ressurecting my ancient thread again!
No worries.

> I have managed to get a bit more time to get a little further with this and
> have a few more questions as a result. I have put a vtkImageCast to float
> into the pipeline as suggested by David and I am now getting results that
> look close to the original GPU volume mapper which is great. Additionally I
> am also now able to render shadows which is really good.
> It would be nice if I didn't need to do the cast as it (presumably) copies
> the data again to perform the conversion to float. Did you get anywhere
> with
> a fix for this?
In 8.1.0 it will directly take uchars, unsigned shorts, floats and doubles.
In master it also takes signed shorts.

> What I am now aiming towards is getting an improved quality fully ray
> traced
> volume render. Something along the lines of what is being achieved here
> (pics about half way down):
> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5110476/
Thanks for the reference. I want to get to that quality too.

As far as I can ascertain, I will need to use the 'pathtracer' renderer type
> rather than 'scivis' to obtain more realistic ray traced results with soft
> shadows and indirect illumination/ambient lighting. The results I am
> getting
> at the moment look quite harsh and the shadows are fairly crude with
> scivis.

> The problem I am having is that the pathtracer renderer seems to need to
> have a material set for it to work, and there is no way to do this for
> volumetric data actors as far as I can see (it is not a member of
> vtkVolumeProperty). I guess it would probably not make sense if it was as a
> medical CT volume may contain many materials (bone, soft tissue, metal
> implants etc).

Does the pathtracer renderer in ospray support volumetric data? I cannot
> seem to get it to render anything in paraview either, wheras the scivis
> renderer in paraview shows the same sort of results I see with my pipeline.

Pathtracer does not yet support volume rendering, only surfaces. The OSPRay
developers are working on it, I expect it will be sometime next year. Once
it does, we will expose materials for volumes too.

Can you offer any guidance with how to proceed with this? Am I limited to
> using something like marching cubes to extract an isosurface for, say the
> skeleton, then doing a surface rendering of this to get the full ray traced
> quality? Would I need to extract an isosurface for each tissue type and
> give
> it an appropriate material? This seems a little long winded, wheras the
> current volume rendering effectively does this with colour and opacity
> lookup tables.
That is how I would proceed at the moment too.

> All that said, the performance is very impressive for a software renderer
> and the results are a step up from the GPU renderer with regards to shadows
> and quality.
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