[vtkusers] Any alternative to vtkUnstructuredGridVolumeRayCastMapper

[Jim]

Hi Ken, Thank you for your input. I am using VTK4.4 official release. I will try the CVS version
soon. vtkUnstructuredGridVolumeRayCastMapper is just too slow and difficult to interact with.
The example IntermixedUnstructuredGrid.tcl can show it all. Another problem is that many
imaging processing classes such as vtkImagePlaneWidget won't accept vtkStructuredGrid
data but vtkImageData only.
 
I really want to  transform my irregularly shaped unstructured volume data into the 
vtkImageData so I can use all powerful image filters. vtkShepardMethod is definitely one
solution. The problem is that vtkShepardMethod generates data in the region where no 
original data is available. SetNullValue and SetMaximumDistance may solve the problem
partially but not entirely. Is there any other way to go?
 
Thanks.
 
Jim


"Moreland, Kenneth" <kmorel at sandia.gov> wrote:
1) Pretty soon (in the next week or two) I plan to check in a projected tetrahedra mapper.  That should be faster, but of lower image quality.  Of course, if you are not using the CVS version of VTK, that will not help for quite a while.
 
2) Hmm, that "wireframe" artifact looks like a bad ray integration.  Are you using VTK 4.4 or the CVS version?  The integration has gotten much better since the last VTK release.
 
Those artifacts can be made less pronounced by making the transfer function less opaque and/or making the colors change more slowly.  If that area where the volume changes from yellow to red is interesting, you may want to consider putting a red isosurface there and then render a yellow volume around that.  The result will probably look quite pleasing and may speed up the rendering a bit.
 
3) Your suggestion of sampling the volume to an image is viable.  That was what many people did before vtkUnstructuredGridVolumeRayCastMapper was around (which was not very long ago).  I never did it, so I can't offer any details.  Maybe someone else can chime in.
 
-Ken
 

   ****      Kenneth Moreland
    ***      Sandia National Laboratories
*********** 
*** *** ***  email: kmorel at sandia.gov
**  ***  **  phone: (505) 844-8919
    ***      fax:   (505) 845-0833




---------------------------------
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On Behalf Of jiksed
Sent: Thursday, April 14, 2005 1:19 PM
To: vtkusers at vtk.org
Subject: [vtkusers] Any alternative to vtkUnstructuredGridVolumeRayCastMapper



Hi vtkusers,
 
I have a 3D volume data in an unstructured grid with irregular surface topography. My first
 instinct is to use vtkUnstructuredGridVolumeRayCastMapper to do the volume rendering. The
 problem is that this volume mapper is extremely slow and the wireframe-type mesh is visible 
in the volume image (please see the attachment). My questions would be:
 
1) Is there any way to speed it up? 
2) How can I make the image more smooth without showing the underline wireframe?
3) Is there any alternative to vtkUnstructuredGridVolumeRayCastMapper? I really need an 
ImageData so I may manipulate the volume opacity and use the ImagePlaneWidget.
 
One way I can think of is to use vtkShepardMethod to transform vtkUnstructuredGrid into 
vtkImageData in a rectangular box. My data is inside an irregular volume like human head. 
Now how do I "get rid of" excessive volume to expose my irregular surface topography? How 
do I manipulate the output of vtkShepardMethod? By setting a small MaximumDistance, some 
points may end up with NullValues but not those points close to the outer surface of my data 
volume. I am kind of lost here. 
 
Thank you for any suggestions.







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