11/13/2008
1
Juraj Obert
http://graphics.cs.ucf.edu/cap4720/fall2008/
11/13/2008
2
Volume Rendering
Rendering until now:
Input:
geometry
textures
shaders
Volume rendering:
Input:
density data in 3D volume
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Volume Rendering: A Deep Dive into Ray Casting and Marching Cubes - Prof. Juraj Obert, Study notes of Computer Graphics
An in-depth exploration of volume rendering, focusing on ray casting and marching cubes techniques. The basics of volume rendering, input data, rendering algorithms, and ray casting on gpus. It also discusses performance issues and adaptive ray marching. Marching cubes are introduced as a method for approximating surfaces, and the document explains the threshold value and implementation details.
Typology: Study notes
Pre 2010
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Juraj Obert
[email protected]
http://graphics.cs.ucf.edu/cap4720/fall2008/
Volume Rendering
Rendering until now:
Input:
geometry
textures
shaders
Volume rendering:
Input:
density data in 3D volume
CT scan
Data storage
3D textures:
same as 2D textures but add yet another
dimension
think of it as a 3D grid
composed of volume elements or voxels
typically store density data
Ray casting cont.
Max Mean First
Ray casting on GPUs
How:
Store 3D volume data in a 3D texture
Map the 3D texture to a 3D box 1-to-
use 3D texture coordinates u,v,w
Integrate contributions along each ray
Ray casting on GPUs
(u,v,w)
(U,V,W)
front faces back faces
Ray casting on GPUs cont.
Pass 1: setRenderTarget(renderTargetBF); cullMode(CULL_FRONT_FACE); setShader(outputTexCoords); render(box);
Pass 2: setRenderTarget(renderTargetFF); cullMode(CULL_BACK_FACE); setShader(outputTexCoords); render(box);
Pass 3: setRenderTarget(frameBuffer); setShader(integrateIntensities); render(quad);
Marching cubes
Approximate surface
by a collection of
“cubes”
Compare density at
each vertex to a
threshold
Marching cubes
How many configurations can we possibly have?
Marching cubes cont.
Implementation:
Definitely not on older GPUs because you
cannot create new geometry
Possible with shader model 4.0 (DirectX 10 and
higher)
The number of cubes determines how
coarse/fine the final surface will be
Marching cubes cont.
Image courtesy of Diane Lingrand
What does the threshold value represent?