[vtk-developers] strange behaviour in vtkVolumeTextureMapper2D

[Lisa Sobierajski Avila]

Hello Sebastien,


>Nope, I've tested that already, replacing the new code with the old 
>(rectangle). No differences, bug remains.

So if you simply alter the vertices (by using size instead of size-1) 
everything works fine?


>BTW : also you might resample the volume and use a LOD to mix both a 
>low-res and hi-res volumeTextureMapper2D, I was wondering if it would be 
>possible to add a parameter for that class that could specify that one 
>just want every 2- or every nth- quad (rectangle) to be used. I guess this 
>would speed up thing, but I do not know about the quality, is it better 
>than resampling to n/2 or n/3 ? I've played with iinc, jinc, and kinc, 
>then changed a couple of tests from == to <=, it looks like it worked, but 
>I'm really not sure about what I'm doing, and as it's a very useful class, 
>I do not want to break it too soon :)

That change can be made (I'd prefer to wait until after finding the current 
bug!) I don't remember why I didn't add that in the first place - I did 
have a reason.... I think it has something to do with the way I traverse 
memory.


>BTW2 : I've sent a mail to the VolumePro guys. Jesus it's expensive !  $ 
>5500 ! (25% discount for university, but wow). Is it really worth it ? We 
>are expecting a GeForce here, and I'm quite impatient to see how it deals 
>with the volumeTextureMapper2D. I'm gonna test it
>with Voodoo 3 this week also.

Is that $5500 US? I thought it was about $3000 US if you got it without any 
special add-ons. But that information is about a year old, so maybe things 
have changed since then.

Whether or not it is worth it depends on your data size, your application 
area and your interactivity requirements. We do get about 10-30 frames per 
second, and the quality is generally better than texture mapping (although 
not as good as ray casting). When we are working with small data sets (64^3 
or 128^3) it is not that important since the texture map version is usually 
rendering about 5-10 frames or so per second with either the full volume or 
a half res version, and it fills in pretty quickly once you stop 
interacting. It is painful when we load a large (256^3 or 512x512x100) data 
set - we do get interactivity using multi-res 2D texture mapping, but with 
much worse quality than the full res volume. The VolumePro still produces 
more than 10 frames per second.

We have two VolumePro boards here, and I feel that I can get things done 
quicker with it (for example, simply loading some data in, setting the 
properties, and generating an image).


Lisa



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