3D computer graphics 3D computer graphics, or “3D graphics,” sometimes called CGI, 3D-CGI or three-dimensional computer graphics are graphics that use a three-dimensional representation of geometric data (often Cartesian) that is stored in the computer for th ...

, popping refers to an undesirable

visual effect Visual effects (sometimes abbreviated VFX) is the process by which imagery is created or manipulated outside the context of a live-action shot in filmmaking and video production. The integration of live-action footage and other live-action foota ...

that occurs when the transition of a 3D object to a different pre-calculated level of detail (LOD) is abrupt and obvious to the viewer.M. Chover, J. Gumbau, A. Puig-Centelles, O. Ripolles, F. Ramos (June 2009) "Rendering continuous level-of-detail meshes by Masking Strips" ''Graphical Models'' pp.185 The LOD-ing

algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...

reduces the

geometrical Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...

complexity of a 3D object the further it is from the viewer and returns that lost complexity as the viewer gets closer to the 3D object, causing it to ''pop'' as it becomes suddenly more detailed. The LOD-ing algorithms can depend on more factors than just distance from the viewer, but it is often the primary factor that is considered. Popping is most obvious when switching between different LODs directly without intermediate steps. Techniques like geomorphing and LOD blending can reduce visual popping significantly by making the transitions more gradual.

LOD Blending

Also known as alpha blending, or alpha compositing this technique reduces popping by displaying both LODs of a

3D model In 3D computer graphics, 3D modeling is the process of developing a mathematical coordinate-based representation of any surface of an object (inanimate or living) in three dimensions via specialized software by manipulating edges, vertices, an ...

simultaneously and blending them together over a small transition period. During the blending process an alpha value is specified for each LOD, which determines transparency of objects. At the beginning of the transition, the initial LOD would have an alpha value of 1.0 (fully opaque) and the new LOD would be have an alpha value of 0.0 (fully transparent). As the viewer approaches the 3D object and reaches the distance when the LOD change would normally occur, the LOD alpha values would gradually switch until the new LOD has an alpha value of 1.0, at which point the initial LOD would no longer be rendered.D. Luebke, M. Reddy, J. D. Cohen, A. Varshney, B. Watson, R. Huebner: Level of Detail for 3D Graphics, Morgan Kaufmann, 2002, It is important to stress that LOD blending only occurs at the distance that a LOD would normally change and only over a small distance. So if during a simulation the LOD change would occur at the 100 units of distance then the LOD blending process would begin at the 95 units of distance and be complete by 105 units of distance. LOD blending has two major disadvantages. It is expensive in terms of

computing power In computing, computer performance is the amount of useful work accomplished by a computer system. Outside of specific contexts, computer performance is estimated in terms of accuracy, efficiency and speed of executing computer program instructio ...

since both LODs are rendered simultaneously for the blend to occur and can be counterproductive since the reason to use LOD-ing algorithms is to reduce the expense of rendering scenes. The technique is not effective when the viewer is close to the 3D object since the blending process will be obviously apparent and result in a visible ghosting effect.

Geomorphing

Geomorphing is a technique that reduces popping during LOD changes by adding approximations of the

to serve as intermediate steps between two LODs to create a smooth transition. Edge collapses (removing vertices) and vertex splits (adding vertices) are the primary operations to modify the 3D model using this method. Traditional geomorphing creates a sequence of 3D models between two LODs. The sequence cannot be interrupted once it has begun and no modifications can be done to it until the LOD change is complete. Due to this restriction, traditional geomorphing is not suited to interactive simulations because the process cannot be quickly reversed if conditions change unexpectedly. Real-time geomorphing directly modifies individual vertices of the 3D model to adjust its LOD. This allows changes made to the geomorph during any frame, either to halt ongoing morphs or initiate further morphs of the 3D model. Since multiple vertices can be triggered to morph independently one of another, certain vertices need to be temporarily locked to ensure a smooth transition occurs, which could result in a delayed LOD change. The flexibility of real-time geomorphing makes it an effective solution for interactive simulations.K. Jeong, S. Lee, L. Markosian, A. Ni (September 2005) "Detail control in line drawings of 3D meshes" ''Springer-Verlag'' pp.700

External links

Example of LOD popping

References

{{Reflist 3D graphic artifacts Computer graphics Game design

LOD Blending

Geomorphing

See also

External links

References