Branko Kaucic

Comparison of viewshed algorithms on regular spaced points

Viewshed is a basic visibility structure and represents all visible points from a given viewpoint. The paper gives a survey of non-parallel viewshed algorithms using regular spaced points. At first, a comprehensive background of the problem is given, then the existing methods (R3, R2, XDraw, method based on the line rasterisation) are introduced briefly. They have been implemented in 11 variants. Real terrain data and fractal generated terrains have been used for their comparison against spent CPU time and the accuracy of a computed visibility information.

Source code plagiarism

Learning programming languages and developing software is important part of curricula at many educational institutions. Directly connected to that is a peer-to-peer sharing of programs source codes which is not always allowed. The article discusses the problem of plagiarism, especially the source code plagiarism and presents an excerpt of the results of the survey among students at Faculty of Education and Faculty of Computer and Information Science at University of Ljubljana and among students at Faculty of Natural Sciences and Mathematics at University of Maribor. Results are revealing alarming situation. In addition, advices for the teachers to avoid the plagiarism as much as possible are presented.

K-guarding of polyhedral terrain

Site visibility analysis is an important research topic with many applications in Geographical Information Systems. This paper introduces a new paradigm in terrain guarding, called k-guarding. K-guarding is a generalization of the classic guarding problem where, instead of only one guard, each surface patch is guarded by at least k guards. Afterwards, two optimization problems based on k-guarding are defined: an optimum k-guarding, and a constrained k-guarding. There are three heuristic approaches—k-greedy add, k-stingy drop, and k-reverse greedy—that are proposed as a solution to the above-mentioned optimization problems. The first two are known approaches adapted to k-guarding, while k-reverse greedy is a new, original heuristic. The heuristics are compared using actual topographic surfaces. It is shown that our approach (k-reverse greedy) gives on average the best near optimum solutions. The most surprising finding of the experiments is that the combination of heuristics introduced here yields even better results.

Interference textures of defects in a thin nematic film: an applet presentation

We have developed an applet presentation showing different structures of a nematic liquid crystal confined to a thin transparent plan-parallel cell. The nematic structures possessing single defects or their pairs may be studied. The corresponding interference textures are shown simulating the polarization optic microscopy experiment. Several parameters defining the experimental set-up can be interactively varied enabling observation of subsequent changes in the interference pattern within a reasonable real time. The basic physics of liquid crystal defects necessary for understanding the limitations of the applet presentation is given.

Fast 3D visualization of road product models

Due to its monolithic nature, 3D visualization software integrated with legacy engineering applications contain every possible feature you might use-whether or not a user really wants them. With the advent of distributed objects and interpreted platform-independent languages such as Java and VRML it is possible to develop cross-platform portable 3D visualization software as components that work in an easy-to-use manner. Adopting these advances, fast 3D visualization can considerably simplify the job of maintaining the life cycle of a road integrated within an agreed road product model. The paper aims to introduce new levels of support to engineers throughout the integrated product life cycle by dealing with issues such as fast platform-independent 3D visualization and product modelling using roads as an example.

On The Lower Bound Of Edge Guards Of Polyhedral Terrains

Guarding polyhedral terrains is a relatively new problem in computational geometry. It is known as NP-hard problem. In 1997, P. Bose, T. Shermer, G. Toussaint and B. Zhu stated the bounds on the number of guards and proposed some algorithms for placing vertex and edge guards. In this contribution, we point to the inconsistency in the proof of the lower bound of the number of edge guards. We show that following the approach of Bose et al. for an n-vertex polyhedral terrain only a weaker lower bound of ⌊(2n−4)/7⌋ can be achieved. Hence deriving the proof for the lower bound equal to ⌊(4n−4)/13⌋ originally stated by Bose et al. remains an open issue.

Ontologizing the Heritage Building Domain

New challenges for cultural heritage have arisen from the expansion of digitalization, the broader range of available applications, and the increase in individuals and organizations interested in obtaining and sharing heritage knowledge. Supporting digital knowledge sharing relating to cultural heritage entails the challenges of structuring and transforming of data to information, information to knowledge and knowledge to application, etc. Digital cultural heritage processes must be knowledge-based and interoperable. Knowledge-based approaches using the concepts of linked data and ontologies are recognized as a basis for efficient solutions.

Approximative terrain guarding with given number of guards

Guarding a surface is a well known optimization problem of the visibility site analysis and has many applications. The basic problem is searching for the minimum number of guards needed to guard (see) the entire surface. More realistic is the guarding where the number of guards is upward limited and the optimization problem is to search for their locations in order to guard as much sur- face as possible. In the paper this problem is treated in de- tails. Several known heuristics (greedy add, greedy add with swap and stingy drop) are re- vised and a new technique called solution im- proving technique is proposed. The technique improves the results of the known algorithms and is used in indirect solving of the problem. Tests on 44 DEMs from USGS DEM Reposi- tory showed that our technique yields compar- ative results for smaller number of guards and better results for higher number of guards.