Anisosurface is a three-dimensional analog of anisoline. It is asurface that represents points of a constant value (e.g.pressure,temperature,velocity,density) within avolume of space; in other words, it is alevel set of a continuousfunction whosedomain is3-space.
The termisoline is also sometimes used for domains of more than 3 dimensions.[1]
Isosurfaces are normally displayed usingcomputer graphics, and are used as data visualization methods incomputational fluid dynamics (CFD), allowing engineers to study features of afluid flow (gas or liquid) around objects, such as aircraftwings. An isosurface may represent an individualshock wave insupersonic flight, or several isosurfaces may be generated showing a sequence of pressure values in the air flowing around a wing. Isosurfaces tend to be a popular form of visualization for volume datasets since they can be rendered by a simple polygonal model, which can be drawn on the screen very quickly.
Inmedical imaging, isosurfaces may be used to represent regions of a particulardensity in a three-dimensionalCT scan, allowing the visualization of internalorgans,bones, or other structures.
Numerous other disciplines that are interested in three-dimensional data often use isosurfaces to obtain information aboutpharmacology,chemistry,geophysics andmeteorology.
Themarching cubes algorithm was first published in the 1987 SIGGRAPH proceedings by Lorensen and Cline,[2] and it creates a surface by intersecting the edges of adata volume grid with the volume contour. Where the surface intersects the edge the algorithm creates a vertex. By using a table of different triangles depending on different patterns of edge intersections the algorithm can create a surface. This algorithm has solutions for implementation both on the CPU and on the GPU.
Theasymptotic decider algorithm was developed as an extension tomarching cubes in order to resolve the possibility of ambiguity in it.
Themarching tetrahedra algorithm was developed as an extension tomarching cubes in order to solve an ambiguity in that algorithm and to create higher quality output surface.
The Surface Nets algorithm places an intersecting vertex in the middle of a volume voxel instead of at the edges, leading to a smoother output surface.
Thedual contouring algorithm was first published in the 2002 SIGGRAPH proceedings by Ju and Losasso,[3] developed as an extension to bothsurface nets and marching cubes. It retains adual vertex within thevoxel but no longer at the center. Dual contouring leverages the position andnormal of where the surface crosses the edges of a voxel to interpolate the position of the dual vertex within the voxel. This has the benefit of retaining sharp or smooth surfaces where surface nets often look blocky or incorrectly beveled.[4] Dual contouring often uses surface generation that leveragesoctrees as an optimization to adapt the number of triangles in output to the complexity of the surface.
Manifolddual contouring includes an analysis of the octree neighborhood to maintain continuity of the manifold surface[5][6][7]
Examples of isosurfaces are 'Metaballs' or 'blobby objects' used in 3D visualisation. A more general way to construct an isosurface is to use thefunction representation.
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