[vtkusers] Help on VTK's Performance: Volume Rendering + Polygonal Object Moving

[Fauze Polpeta]

Right David...I will try the two alternatives you mentioned:

1) Texture volume rendering

2) VTKEdge

One last question: In order to achieve GPU-based ray casting I just have to
configure and "embed" VTKEdge into my project or have to re-write my volume
rendering application? In orther words, for GPU-based ray casting VTKEdge is
saw as a GPU backend interface library, or/and as a new set of
abstractions/filters to be deployed by the programmer?

Thank you so much

My Best Regards

Fauze

On Fri, Jan 22, 2010 at 7:47 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi Fauze,
>
> I've written surgical tracking application with volume rendering, and
> I've always used texture volume rendering in preference to ray casting
> in order to avoid the issues that you describe, since the LOD approach
> doesn't work very well when the tools are in constant motion.  For our
> next generation of surgical applications, we intend to use VTKEdge for
> doing GPU-based ray casting.
>
> Mixing pure OpenGL with VTK isn't a good idea, since you can't really
> know what the OpenGL state will be.  Also, if you're instruments ever
> intersect the volume (as I'm sure they would) you will get an
> incorrect rendering unless you allow VTK to properly intermix the
> polygon rendering with the the volume.
>
> In short: if you really need to use ray casting, try out VTKEdge.  I
> don't think it's a good idea to try to write your own polydata/volume
> intermixing code.
>
>    David
>
>
>
> On Fri, Jan 22, 2010 at 2:32 PM, Fauze Polpeta <fauze.polpeta at gmail.com>
> wrote:
> > Thanks for your support David and sorry for the cross-post...I was
> wondering
> > if one could image some core-based solution.
> > In our case a medical application is being prototyped and the ray-cast
> > volume was preferred for volumetric reconstruction. The point is that our
> > application is connected to a device that tracks surgical instruments
> that
> > are represented by polydata. So, theoretically, we can't abdicate of the
> > ray-casting while moving these tools during a given surgical procedure.
> This
> > is the reason I mentioned if it is possible to bypass the pipeline
> > processing in order to render this polydata using pure OpenGL commands.
> > Thanks again
> > Regards
> > Fauze
> >
> >
> > On Fri, Jan 22, 2010 at 7:04 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
> >>
> >> Hi Fauze,
> >>
> >> Please don't cross-post to the vtk-developers list, since that list is
> >> only for developer issues.
> >>
> >> Mixing polygonal objects with software ray-cast volume rendering is an
> >> expensive process, it involves reading a partially rendered scene from
> >> the video card back to main memory and re-doing the volume rendering
> >> using the information in the depth buffer.  Every time the object
> >> moves, the ray-cast has to be redone.
> >>
> >> If you need fast volume rendering intermixed with polydata, you should
> >> use vtkVolumeTextureMapper3D or vtkVolumeTextureMapper2D.  These
> >> volume mappers do all of the polydata/volume intermixing right on the
> >> graphics cards.
> >>
> >> What I often do is use a vtkLODProp3D so that I can use the texture
> >> volume rendering when I'm dragging things, but have it automatically
> >> switch to ray-casting when I stop dragging the mouse.
> >>
> >>  David
> >>
> >>
> >> On Fri, Jan 22, 2010 at 1:33 PM, Fauze Polpeta <fauze.polpeta at gmail.com
> >
> >> wrote:
> >> > Dear VTK Users;
> >> > I have worked on a project that requires a Polygonal Object ( or at
> >> > least a
> >> > simple Line ) to be moved on the fly on a volume rendered scene built
> on
> >> > top
> >> > of a vtkVolumeRayCastMapper abstraction.
> >> > This goal was successfully reached but we have faced a drastic
> >> > performance
> >> > degradation when moving the polygonal object into/across the volume
> >> > scene.
> >> > We have assumed this is a consequence of the VTK's pipeline
>  processing
> >> > model. If anyone confirm that, we would like to ask any help in the
> >> > sense of
> >> > pointing any strategy for achieving any (minimal) performance
> >> > improvement.
> >> > Perhaps, getting the OpenGL Context and rendering our polygonal object
> >> > using
> >> > OpenGL commands; thus skipping the VTK's pipeline processing. Is this
> >> > feasible?
> >> > Thanks in advance for any help.
> >> > Regards,
> >> > Fauze
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> >
> >
>
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