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"Volume Graphics"
IEEE Computer, Vol. 26, No. 7
July 1993
pp. 51-64

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Sidebar:  Glossary

The terms in this glossary are defined in the context of volume graphics. Their general and formal definition is not necessarily reflected in the definition given here. Words italicized in the definitions are defined under their own entries in this glossary.

adjacency: a relation between two voxels which are said to be 6-adjacent if they share a face, 18-adjacent if they share a face or an edge, and 26-adjacent if they share a face, an edge, or a vertex.

connectivity: a relation between two voxels which are said to be 6-connected (18-connected, 26-connected) if there exists a 6-path (18-path, 26-path) between them.

hybrid (intermixed) voxel model: a volumetric dataset in which a synthetic voxelized model is intermixed with sampled or computed data.

neighborhood: the 6-neighborhood (18-neighborhood, 26-neighborhood) of a voxel is the set of all voxels that are 6-adjacent (18-adjacent, 26-adjacent) to it.

path: a sequence of voxels is a 6-path (18-path, 26-path) if every two consecutive voxels along the sequence are 6-adjacent (18-adjacent, 26-adjacent).

raster graphics: a subfield of computer graphics that represents the scene by a 2D array (raster) of pixels stored in a 2D frame-buffer.

ray casting: a volume viewing algorithm in which sight rays are cast from the viewing plane through the volume. The tracing of the ray stops when the visible voxels are determined by accumulating or encountering opaque value.

ray tracing (3D raster ray tracing, discrete ray tracing, volumetric ray tracing): a volume viewing algorithm in which light behavior is simulated by recursively tracing individual imaginary rays of light as discrete lines through the scene represented in a volume buffer (see Discrete Ray Tracing).

surface rendering: an indirect technique used for visualizing volume primitives by first converting them into an intermediate surface representation and then rendering them to the screen by employing conventional computer graphics techniques (cf. volume rendering).

three-dimensional discrete topology: the formal topological characterizations of the digital voxel space that conform as closely as possible to the corresponding characterizations used in the topology of the continuous three-dimensional space.

tunnel: a 3Dpath of certain connectivity that penetrates a discrete surface. Surface thickness is defined by the absence of particular tunnels in it.

vector graphics: a subfield of computer graphics that represents the scene by a set of lines (vectors) that are repeatedly redrawn to the screen by a random vector generator.

visualization: a method of extracting meaningful information from complex datasets through the use of interactive graphics and imaging.

volume buffer (3D raster, cubic frame buffer): a 3D array of voxels used for storing a regular volumetric dataset.

volume modeling:The synthesis, analysis, and manipulation of sampled, computed, and synthetic objects contained within a volumetric dataset.

volume rendering: a direct technique for visualizing volume primitives without any intermediate conversion of the volumetric dataset to surface representation (cf. surface rendering).

volume visualization: a visualization method concerned with the representation, manipulation, and rendering of volumetric data.

volumetric dataset: the aggregate of voxels tessellating the volume.

volume graphics: the subfield of computer graphics that employs a volume buffer for scene representation and is concerned with synthesizing, manipulating, and rendering such scenes. Volume graphics is the 3D counterpart of raster graphics.

voxblt (voxel block transfer): A set of operations by which a rectangular sub-volume of voxels (called a "room") can be copied within the volume buffer with arbitrary write modes and maskings. Voxblt is the 3D counterpart of the 2D bitblt (bit block transfer).

voxel: an abbreviation for 'volume element' or 'volume cell.' Each voxel is a quantum unit of volume and has a numeric value (or values) associated with it that represents some measurable properties or independent variables of a real object or phenomenon. The voxel is the 3D conceptual counterpart of the 2D pixel.

voxel space: a 3D integer grid or lattice of voxels in which the volumetric dataset (the object) resides.

voxelization (volume synthesis, 3D scan-conversion): the process of converting a geometric representation of a synthetic model into a set of voxels that "best" represents that synthetic model within the discrete voxel space (see Fundamentals of Voxelization sidebar ).

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