Levels of detail (LOD) engineering of VR objects

Abstract

For real-time performance, virtual reality systems often employ various performance optimization techniques. One of the most popular methods is using geometric models with different "Levels of Detail (LOD)". In a previous paper by this author [l], we have proposed to use software engineering principles such as the concept of hierarchical and incremental modeling, and simultaneous consideration of form, function and behavior for modeling VR objects. Each refinement stage driven by such a modeling philosophy produces step-by-step form, function and behavior specifications of a VR object. We can make good use of these by-products as LOD for adaptive display and simulation by additionally specifying conditions for LOD switching. These specifications can be simulated and analyzed in advance for an estimation of performance for a given VR execution environment. Such an engineering process deals with behavior and geometry together; different geometric LOD may possess different behaviors and vice versa. A certain function or behavior might dictate an inclusion of a particular geometric feature that may not be possible to preserve, if the geometric LOD were to created in a bottom-up fashion (e.g. using the mesh simplification algorithms). We demonstrate our approach by modeling an automobile object with three levels of geometric and behavior detail in a top-down manner, simulate their instances in a small virtual town, and based on the simulation result, make predictions to the maximum allowable number of vehicles that will maintain an acceptable frame rate if executed in a faster simulation environment. We believe that our approach combines the idea of hierarchical refinement of virtual objects and the use of LOD in a very natural and intuitive manner.

Design on Geographical Multi-Scale 3D Symbol Library

“…The main advantage of particle systems is not only that complex objects can be constructed by using simple body elements, but also that particle systems provides a strong and powerful means to resolve the natural events modeling, such as fire, water, rain, snow, grass and trees and so on. A particle system is composed of a large number of simple voxels called particles [8]. Each particle has a set of attributes such as position, speed, color and lifecycle.…”

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“…Note that the ow and number of re nements (or the number of LODs) may vary according to the intent of the developer, and, as long as the "compatibility" condition is kept, any geometric and any behavior model can be combined. In fact, we rede ne LOD as a particular combination of two compatible geometric and behavior models (see table 2) (Seo & Kim, 1999).…”

“…It combines several concepts, both old and new, such as simultaneous consideration of form, function, and behavior, hierarchical modeling and top-down creation of LODs (Seo & Kim, 1999), incremental simulation and performance tuning, user task and interaction modeling, consistency checking between physical devices and virtual interaction objects, and compositional reuse of VR objects (Seo, Kim, & Kim, 2001). The basic underlying modeling principle is to design VR objects and the scenes they compose by considering their realism, presence, behavioral correctness, performance, and even usability, as early as possible.…”

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