Scientific Visualization Tutorial
Volume Visualization
Volume rendering is used to view 3d data without the usual intermediate
step of deriving a geometric representation which is then rendered. The
volume representation uses voxels, or volume elements to determine visual
properties, such as opacity, color, shading at each point in the computational
domain. Several images are created by slicing the volume perpendicular
to the viewing axis at a regular interval and compositing together the
contributing images from back to front, thus summing voxel opacities and
colors at each pixel. By rapidly changing the color and opacity transfer
functions, various structures are interactively revealed in the spatial
domain.
Volumetric rendering
Volumetric rendering allows the entire data set to be viewed at once,
and lets the user "see inside" the data. For each pixel in an image created
using volumetric rendering, a ray is cast through the semi-transparent
volume. The resulting color at the pixel is a composite of all the voxels
the ray has intersected. As a consquence, such images tend to be blurry.
Another characteristic volumetric rendering is that it is typically slower
than surface rendering techniques. Therefore, volumetric rendering of adata
set is often not well suited for realtime visualization. However, it does
provide features that are obscured by surface rendering techniques.