Borut alik

An efficient chain code with Huffman coding

This paper presents a new chain code based on the eight-direction Freeman code. Each element in the chain is coded as a relative angle difference between it and the previous element. Statistical analysis showed that the probabilities of the Freeman codes differ importantly. Therefore, the Huffman coding was applied. The proposed chain code requires 1.97bits/code, its chain length is short, it allows the representation of non-closed patterns, and it is rotationally independent.

Compressed vertex chain codes

This paper introduces three new vertex chain codes. Firstly, considering that the vertex chain code uses 2 bits to represent only three code elements, a new code is introduced without increasing the average bits per code. The second case introduces a variable-length vertex chain code. Finally, a new compressed chain code is proposed based on the Huffman method. The continuation introduces a method for quantificationally evaluating the efficiency of chain codes. The efficiencies of the new vertex chain codes are then compared theoretically and practically against the most popular chain codes. The result of the comparison shows that the new compressed chain code is the most efficient.

An algorithm for polygon clipping, and for determining polygon intersections and unions

This paper introduces a universal algorithm for polygon clipping, which is a frequent operation in GIS. In the proposed solution, the clipping polygons can be concave and may include holes. This algorithm is based on so-called entry/exit intersection point property, which has to be explicitly determined only at the first calculated intersection point. It uses a simple but efficient data structure based on a single-linked list. Boolean union and the difference between input polygons can also be determined after small modifications. This algorithm can easily be adapted to Boolean operations between regions composed of polygon sets.

Point-in-polygon tests for geometric buffers

The point-in-polygon problem is often encountered in geographical information systems. The algorithms usually work on polygons defined by straight edges. In some situations, however, polygons containing circular arcs are applied. In geographical information systems these polygons are usually considered as geometric buffers, geodesic offsets, or geodesic parallels. This paper presents three algorithms suitable for providing information about the containment of a point in geometric buffers: the Ray-crossing method, the Cell-Based Algorithm and the Approximate approach. An extensive experimental section allows the reader to select the most efficient algorithm for practical problems.

Visualization of LIDAR datasets using point-based rendering technique

Remote sensing technologies, such as LIDAR, rapidly evolve and produce large datasets. The computers used to visualize these data have limited resources, which prevent detailed and real-time visualization. An approach to real-time visualization of virtually unlimited LIDAR datasets, at full detail with a hierarchical and out-of-core approach to data management and a modern point-based rendering technique, is presented. It is based on on-demand loading of data subsets into their optimal memory locations and on a two-pass point-based rendering method that utilizes elliptical weighted average filtering to reduce alias. In addition, points are rotated in accordance to their distance and orientation from the viewer. All graphics computations are implemented in programmable shaders on the GPU, so the CPU is free to perform other tasks. The capability of our approach is compared with the Kreylos et al. (2008) method.

Reconstructing domain boundaries within a given set of points, using Delaunay triangulation

Given an input set of planar points, which occupy a non-convex polygon area, possibly with holes, we reconstruct the shape of its boundary domain, without previous knowledge of which points or edges belong to the boundary. Our approach is based on different qualities of the Delaunay triangles inside and outside the domain. This method is heuristic and does not ensure success in all cases but it is very simple and there is no other method for this problem known to us. The method was derived on real GIS data but experiments show that it could also be used for mechanical engineering data, with positive results.

Chain code lossless compression using move-to-front transform and adaptive run-length encoding

Chain codes are the most size-efficient representations of rasterised binary shapes and contours. This paper considers a new lossless chain code compression method based on move-to-front transform and an adaptive run-length encoding. The former reduces the information entropy of the chain code, whilst the latter compresses the entropy-reduced chain code by coding the repetitions of chain code symbols and their combinations using a variable-length model. In comparison to other state-of-the-art compression methods, the entropy-reduction is highly efficient, and the newly proposed method yields, on average, better compression.

A hybrid evolutionary algorithm for tuning a cloth-simulation model

Abstract: Textile simulation models are notorious for being difficult to tune. The physically based derivations of energy functions, as mostly used for mapping the characteristics of real-world textiles on to simulation models, are labour-intensive and not guarantee satisfactory results. The extremely complex behaviour of textiles requires additional adjustment over a wide-range of parameters in order to achieve realistic real-life behaviour of the model. Furthermore, such derivations might not even be possible when dealing with mass-spring particle system-based models. Since there is no explicit correlation between the physical characteristics of textiles and the stiffnesses of springs that control a models behaviour, this remains an unresolved issue. This paper proposes a hybrid evolutionary algorithm (EA), in order to solve this problem. The initial parameters of the model are written in individuals genes, where the number of genes is predefined for different textile types in order to limit the search-space. By mimicking the evolution processes, the EA is used to search the stability domain of the model to find a set of parameters that persuasively imitate the behaviour of a given real-world textile (e.g. silk, cotton or wool). This evaluation is based on the drape measurement, a characteristic often used when evaluating fabrics within the textile industry. The proposed EA is multi-objective, as textile drape is analysed using different quantifications. Local search is used to heuristically improve convergence towards a solution, while the efficiency of the method is demonstrated in comparison to a simple EA. To the best of our knowledge, this problem is being solved using an EA for the first time.

Directional difference chain codes with quasi-lossless compression and run-length encoding

This paper considers a new contour-based representation of binary objects in raster images. Low processing and storage requirements of the decoder, satisfactory compression ratio and generality make this chain coding technique interesting for storing predefined graphical objects in embedded systems. Three improvements of the DDCC code were introduced. Extra Huffman codes are assigned to two frequent pairs of symbols, 135^o directional differences in concave angles are omitted since they do not affect the outer object shape and, finally, longer line segments are run-length encoded. Comparison with six other chain coding techniques of similar implementation complexity confirms that the new technique represents an efficient alternative way to encode 8-connected contours.

An efficient raster font compression for embedded systems

This paper presents a new lossless raster font compression method that uses vertex chain code to define characters outline. Obtained chain codes are compressed by Huffman coding algorithm. The results show that the new method requires least memory space to store the raster fonts among the known methods. Moreover, the font size has almost no impact on the coder efficiency. Due to the low complexity of the decoder that occupies only 2.7kB of memory space, this method is ideal for use in embedded systems.