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.