TAPESTRY: The Art of Representation and Abstraction
Data Types - Voxels
What's it all about?
Certain devices that are available to capture 3D data, mostly in the medical field, do so by (conceptually) dividing the object (usually a person) up into thin slices and measuring something (magnetic resonance, etc.) in a grid within that slice. A series of slices provides a complete view of the subject.
The sample region, a volume, is analagous to the 2D screen or scanner elements we call pixels (which is, itself, short for "picture element"). They are called "voxels", a somewhat tortured derivation of "volume element".
You'll notice that this data type is not common in architecture, though it is a useful foundation for computational fluid dynamics (CFD) and certain other analyses. There are almost no sources of voxel data at building scale except through "slicing" of polygon data.
Primitives
As indicated above, the pimitive of these systems is nothing but a small volume, like a sugar-cube. Unlike a sugar-cube model, in which there are cubes and empty space, you should visualize a voxel model as a 3D stack of sugar cubes, some of which contain one value, and some another (some of the sugar-cubes might be "invisible" for example).
Attributes
The voxels are usually measured by some automated system, such as a CT-Scan, MRI-scanner, etc. The value they contain relates to whatever that device measures, but the associated visualization software might render the information as a 3D surface, as "slices", etc. Combining multiple measuring tools might give voxels multiple values, but this is not common.
Organization
The raw voxel data is only organized as a space-filling collection of values, similar to the way an 8-bit grayscale scan of an image is just a series of values between 0 and 256 (for example).
As with 2D images, manipulating voxel data often involves finding or traversing boundaries between regions with differing attribute values (e.g., finding the surface of your brain, or kidneys). Such surface reconstructions can be quite complex and computationally demanding.
Examples
None of the common architectural modeling programs in use today offers voxel data as a primitive data type. However, this is exactly what 3D deposition printers do during output, and there are tools (3D-Coat) in the gaming and animation world that begin to address these features.
Last updated: April, 2014
