[vtkusers] Rendering multiple volumes

[peterm]

Hello

Are you sure it is possible in general to do volume rendering on 2 volumes
independently and create the composite image in a meaningful way? Imagine
you have 2 cubical volumes on top of each other with constant intensity and
a constant 1 opacity transfer function. In case you image them from the top
direction you would get a square with constant color according to the color
transfer function of the first volume. If you render it from the bottom you
get similar results, but this time it depends on the color transfer function
of the bottom volume.

So the point is that the order in which the ray traverses the volume
actually matters, and thus proper compositing cannot be achieved without
depth information (e.g. alpha blending the results will yield bad results).
Thus the volume renderer has to know about all the volumes you would like to
render at a specific step along the sampling ray and individual mappers
cannot be used for the problem.

The first hit google gives for the topic [1] seems to apply an intermixed
set of sampling slices to solve the before mentioned problem. You could use
a volume slicer filter or vtkProbeFilter to obtain the images along the the
intersection planes and do the compositing.

Peter

[1] GPU-based Multi-Volume Rendering for the Visualization of Functional
Brain Images
http://www.google.de/url?sa=t&source=web&cd=1&ved=0CBsQFjAA&url=http%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.87.9496%26rep%3Drep1%26type%3Dpdf&rct=j&q=volume%20rendering%20multiple%20volumes&ei=WD97TuOJCM_pOYKwubkC&usg=AFQjCNGFRF1wnJhfU3OD4Qfv65y-CKlWAw&sig2=H5YJdfvN0Q-MAH_v8t0hFQ&cad=rja



--
View this message in context: http://vtk.1045678.n5.nabble.com/Rendering-multiple-volumes-tp4829710p4830288.html
Sent from the VTK - Users mailing list archive at Nabble.com.