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Voxel 245
Voxel data
A (smoothed) rendering of a data set of voxels for
a macromolecule
relating to the same voxel positions.
A voxel represents the sub-volume box with constant scalar/vector
value inside which is equal to scalar/vector value of the corresponding
grid/pixel of the original discrete representation of the volumetric data.
The boundaries of a voxel are exactly in the middle between
neighboring grids. Voxel data sets have a limited resolution, as precise
data is only available at the center of each cell. Under the assumption
that the voxel data is sampling a suitably band-limited signal, accurate
reconstructions of data points in between the sampled voxels can be
attained by low-pass filtering the data set. Visually acceptable
approximations to this low pass filter can be attained by polynomial
interpolation such as tri-linear or tri-cubic interpolation.
The value of a voxel may represent various properties. In CT scans, the
values are Hounsfield units, giving the opacity of material to X-rays. [1]
:29 Different types of value are acquired from MRI or ultrasound.
Voxels can contain multiple scalar values - essentially vector data; in
the case of ultrasound scans with B-mode and Doppler data, density,
and volumetric flow rate are captured as separate channels of data
Other values may be useful for immediate 3D rendering, such as a surface normal vector and color.
Uses
Common uses of voxels include volumetric imaging in medicine and representation of terrain in games and
simulations. Voxel terrain is used instead of a heightmap because of its ability to represent overhangs, caves, arches,
and other 3D terrain features. These concave features cannot be represented in a heightmap due to only the top 'layer'
of data being represented, leaving everything below it filled (the volume that would otherwise be the inside of the
caves, or the underside of arches or overhangs).
Visualization
A volume containing voxels can be visualized either by direct volume rendering or by the extraction of polygon
iso-surfaces which follow the contours of given threshold values. The marching cubes algorithm is often used for
iso-surface extraction, however other methods exist as well.
Computer gaming
• C4 Engine is a game engine that uses voxels for in game terrain and has a voxel editor for its built in level editor.
C4 Engine uses a LOD system with its voxel terrain that was developed by the game engine's creator. All games
using the current or newer versions of the engine have the ability to use voxels.
• Upcoming Miner Wars 2081 uses their own Voxel Rage engine to let the user deform the terrain of asteroids
allowing tunnels to be formed.
• Many NovaLogic games have used voxel-based rendering technology, including the Delta Force, Armored Fist
and Comanche series.
• Westwood Studios' Command & Conquer: Tiberian Sun and Command & Conquer: Red Alert 2 use voxels to
render most vehicles.
• Westwood Studios' Blade Runner video game used voxels to render characters and artifacts.