[vtkusers] Odd geometric effects in volume rendering

[Jim Geach]

Dear list, 

I'm experiencing some weird effects in volume rendering of very large volumes (cosmological simulations). I have 64 bit indexing turned on, and the volume (of the correct size) renders, but I'm seeing weird geometric effects, kind of like discontinuities. This does not appear in the same data at a lower resolution, and independent tests confirm that the strange artifacts are not in the underlying data being rendered.

I show an example at: 

http://dl.dropbox.com/u/59256622/volume.png 

where you can see an example rendering. 

The clearly defined horizontal and vertical artifacts should not be there. Similarly, there appear to be discontinuities (black gaps) in the volume.

I'm using vtkFixedPointVolumeRayCastMapper() and composite blending.

Is this a 64 bit volume rendering bug, and if so, would it be easy to fix? I'm using version 5.11.0 of the code.

Thanks, Jim Geach

---
Dr James Geach
McGill University

Ernest Rutherford Building,
3600 Rue University, Montreal, QC

jimgeach at physics.mcgill.ca
514-398-1449
http://www.physics.mcgill.ca/~jimgeach