No abstract

Backward polygon beam tracing methods, that is beam tracing from the light source (L), are well suited to gather path coherency from specular (S) scattering surfaces. These methods are useful for modelling and efficiently simulating caustics on diffuse (D) surfaces; an effect due to LS + D transport paths. This paper generalizes backward polygon beam tracing to include a glossy (G) scattering surface. To this end the details of a beam tracing lumped model and implementation of L(S | G)D transport paths are presented.Although we limit the discussion to short transport paths, we show that backward beam tracing is faster than photon mapping by an order of magnitude for rendering caustics from glossy and specular surfaces.

The generation of accurate Line of Sight (LOS) visibility information consumes significant resources in large scale synthetic environments such as many-on-many serious games and battlefield simulators. Due to the importance of optimum utilisation of computing resources, a number of LOS algorithms are reported in the literature to either efficiently compute LOS information or reduce the impact of LOS queries on the run-time performance of synthetic environments. From the literature it is known that a k-dimensional tree (kd-tree) based raytracing approach, to calculating LOS information, is efficient.A new implicit min/max kd-tree algorithm is discussed for evaluating LOS queries on large scale spherical terrain. In particular the value of low resolution boundary information, in quickly evaluating the LOS query, is emphasised. The min/max algorithm is empirically compared to other LOS approaches that have either implicitly or explicitly used kd-trees to optimise LOS query evaluation. The min/max algorithm is shown to have comparable performance to these existing LOS algorithms for flat earth, but improved performance when the application domain is extended to spherical earth. An average of a factor 3.0 performance increase is experienced over that of the existing implicit and explicit max kd-tree algorithms on spherical earth. This is achieved by combining the existing kd-tree algorithm with the classic smooth-earth LOS obscuration test and from there the min in min/max kd-tree.

The paper presents a hierarchical naive Bayesian and lexicon based classifier for short text language identification (LID) useful for under resourced languages. The algorithm is evaluated on short pieces of text for the 11 official South African languages some of which are similar languages. The algorithm is compared to recent approaches using test sets from previous works on South African languages as well as the Discriminating between Similar Languages (DSL) shared tasks' datasets. Remaining research opportunities and pressing concerns in evaluating and comparing LID approaches are also discussed.

The implementations of a couple of often used Bidirectional Reflectance Distribution Functions (BRDFs) are numerically verified against the three conditions for physical plausibility. These conditions are positivity, symmetry (sometimes referred to as reciprocity) and conservation of energy. The focus of this paper is the numerical tests implemented to analyse and verify the BRDF implementations as physically plausible. A concise list of BRDF formulas, modified as required for physical plausibility, is however also presented which to the authors' best knowledge has not yet been presented in the literature.