ray casting with surface geometry

[Lisa Sobierajski Avila]

Hello Dimitris,

If you ray cast a volume with opaque surface geometry in the scene, the 
geometry is taken into consideration. At the end of geometric rendering, 
the color/depth buffer is captured and used to bound the end points of the 
rays that are cast. There is no need to use a ray bounder - this is only 
necessary if you want to clip the rays against some "invisible" geometry 
(with some limitations in shape) - for example to have a "sphere of interest".

Some things to watch out for: you cannot intermix translucent geometry with 
volumes, you cannot have two volumes that overlap, you have to turn 
back-to-front sorting on in the culler if you want more than one texture 
mapped volume.

Lisa


At 10:23 AM 4/17/00 +0100, Dimitris Agrafiotis wrote:
>Dear All
>
>I have the following question.
>
>I have two different volumetric datasets (both structured points) and
>using the sane renderer I render one of them using ray casting and from
>the other I extract an opaque surface (triangles) using a contouring
>filter (e.g. marching cubes). I am not sure about the result I am
>taking. Are the rays bounded by the surface? Or does the renderer just
>ray cast the whole volume, produces the pixel values, then constructs
>the surface geometry and the pixel values for the other dataset and
>then composites the resulting pixel arrays? And wouldn't the second
>case be incorrect since the rays would have taken in consideration
>points that are not actually visible?
>
>If I want to bound the rays do I have to use the
>vtkProjectedPolyDataRayBounder object?
>
>Finally, I am using vtk 2.4. If I switched to vtk 3.1 and used the
>TextureMapper2D for the ray casting part would then everything be OK?
>
>Please forgive me if there is something fundamentally wrong in what I am
>saying.
>
>Thanks in Advance
>Dimitris
>
>
>----------------------
>Dimitris Agrafiotis
>University of Bristol
>Department of Electrical & Electronic Engineering
>Merchant Venturers Building
>Woodland Road, Bristol BS8 1UB, UK
>Phone:  (+ 44 117) 9545194
>E-mail: d.agrafiotis at bristol.ac.uk
>
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