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Item Simple Derivation of the Hermite Bicubic Patch using Tensor product(2025) Skala, VáclavBicubic parametric patches are widely used in various geometric applications. These patchesare critical in CAD/CAM systems, which are applied in the automotive industry and mechanical andcivil engineering. Commonly, Hermite, B ́ezier, Coons, or NURBS patches are employed in practice.However, the construction of the Hermite bicubic patch is often not easy to explain formally. Thiscontribution presents a new formal method for constructing the Hermite bicubic plate based on thetensor product approach
Item An Efficient point-in-convex 3D polyhedron test using a projective algorithm with sub-linear expected complexity(2025) Skala, VáclavWe propose a novel algorithm for determining whether a given point lies within a convex polyhedron, achieving a sub-linear computational expected complexity of Oexp(N1/2), where N represents the number of triangles in the polyhedron’s triangular mesh. In contrast to traditional methods with linear complexity O(N), our approach significantly reduces com-putational overhead, making it especially effective for large polyhedral models. The algorithm is formulated entirely in projective space, utilizing homogeneous coordinates for the tested points and triangle vertices. By leveraging vector–vec¬tor operations optimized for SSE, AVX instructions, and GPU architectures, our method is robust and straightforward, tailored to handle even highly complex convex polyhedra. The efficiency of the approach was validated through theoretical analysis and estimated speed-up calculations, demonstrating its potential to accelerate applications in computer graphics, computational geometry, collision detection, and related fields. Additionally, the simplicity of the proposed algorithm ensures a high potential for broad applicability and supports further advancements in this area.
Item Register-Based and Stack-Based Virtual Machines: Which Perform Better in JIT Compilation Scenarios?(2025) Šimek, Bohuslav; Fiala, Dalibor; Dostal, MartinBackground: Just-In-Time (JIT) compilation plays a critical role in optimizing the performance of modern virtual machines (VMs). While the architecture of VMs – register-based or stack-based – has long been a subject of debate, empirical analysis focusing on JIT compilation performance is relatively sparse. Objective: In this study, we aim to answer the question: “Register-based and stack-based virtual machines: which perform better in JIT compilation scenarios?”. Methods: We explore this through a comprehensive set of benchmarks measuring execution speed. To achieve this, we developed identical test cases in languages that support both types of VM architectures and ran these tests under controlled conditions. The performance metrics were captured and analyzed for JIT compilation, including initial interpretation, bytecode translation, and optimized code execution. Results: Our findings suggest that register-based VMs generally outperform stack-based VMs in terms of execution speed. Moreover, the performance gap between the two architectures in mixed execution mode, which essentially copies characteristics of the underlying virtual machine, suggests that making the right choice of VM architecture is still important. Conclusion: This study provides developers, researchers, and system architects with actionable insights into the performance trade-offs associated with each VM architecture in JIT-compiled environments. The findings can guide the design decisions in the development of new virtual machines and JIT compilation strategies.Item Robust Line-Convex Polygon Intersection Computation in E2 using Projective Space Representation(2023) Skala, VáclavThis paper describes modified robust algorithms for a line clipping by a convex polygon inE2and a convex polyhedron inE3. The proposed algorithm is based on the Cyrus-Beck algorithmand uses homogeneous coordinates to increase the robustness of computation. The algorithm enablescomputation fully in the projective space using the homogeneous coordinates and the line can be givenin the projective space, in general. If the result can remain in projective space, no division operation isneeded. It supports the use of vector-vector operations, SSE/AVX instructions, and GPU.Item A New Fully Projective O(lg N) Line Convex Polygon Intersection Algorithm(2025) Skala, VáclavIntersecting algorithms, especially line clipping in E2 and E3 in computer graphics, have been studied for a long time. Many different algorithms have been developed. The simplest case is a line clipping by a convex polygon in E2 with O(N) computational complexity and with known polygon edges orientation. This contribution presents a new algorithm for a line clipping by a convex polygon in E2 with O(lg N) complexity, which is based on the point-in-half plane test. The proposed algorithm does not require prior knowledge of the polygon edge orientation. The vertices of the convex polygon and the clipped line can be given in projective space using homogeneous coordinates. The algorithm uses vector–vector operations for efficient implementation with SSE or AVX vector–vector instructions or on GPUs.Item A new fully projective O(log N) point-in-convex polygon algorithm: a new strategy(2025) Skala, VáclavA novel and fully projective algorithm for a point-in-convex polygon test with computational complexity of O(log N) in 2D isdescribed in this contribution. The polygon vertices and tested points can be given in projective space without conversion toEuclidean space. The proposed algorithm is simple, robust, easy to implement, and invariant to the convex polygon orientation.It can be easily modified for use in Euclidean space and CPU implementation. Vector–vector operations are used, makingit suitable for implementation using SSE, AVX, and FMA instructions.Item On self-supervision in historical handwritten document segmentation(Springer, 2025) Baloun, Josef; Prantl, Martin; Lenc, Ladislav; Martínek, Jiří; Král, PavelItem Russian Publications in Web of Science: A Bibliometric Study(2023) Fiala, Dalibor; Maltseva, DariaThis article presents a bibliometric study of 1.38 million Russian publications indexed in Web of Science as of May 2022 without any restrictions as to document types, time periods, scientific disciplines, etc. From this perspective, the present analysis reflects Russian research’s true presence and visibility in the most prestigious scientific literature database. The main results obtained are: a) There was a rapid increase in research production in the 2010s, but the share of the Russian output in the global research production is still below 3%. b) International collaborative publications account for about 30% of Russian papers but around 70% of Russian citations. c) Physics, chemistry, and engineering are the most productive Russian research areas, but their citation impact is below the world average in those respective fields. d) The most frequently collaborating countries are the United States, Germany, and France, but Canada and Switzerland consistently contribute to the greatest relative citation impact of collaborative papers in the top ten research areas.Item Analysis of Cited References in Russian Publications on Web of Science(2024) Fiala, Dalibor; Maltseva, DariaIn this article we analyze the cited references in 1.38 million papers by Russian (co-)authors indexed in the Web of Science database until May 2022. Similarly, to the established processes in the so-called Reference Publication Year Spectroscopy (RPYS), we study the distribution of the references across the cited years and seek to identify the peak years with the publications that attracted the most attention of Russian scholars. In this way, the historical roots of Russian science may be traced and we take a closer look at these most influential works. In addition, we investigate the evolution of the mean age of references and of their average number per paper over time and inspect the most frequently cited sources. The results show that the average number of references in Russian papers has been steadily increasing, but the mean age of references has been declining in the most recent years. Also, the foundations of Russian science seem to be physics of particles and electrochemistry and have recently become based more internationally than in the past. This study is the first of its kind and may help better understand the character of Russian research.Item Editing mesh sequences with varying connectivity(2024) Hácha, Filip; Dvořák, Jan; Káčereková, Zuzana; Váša, LiborTime-varying connectivity of triangle mesh sequences leads to substantial difficulties in their processing. Unlike editing sequences with constant connectivity, editing sequences with varying connectivity requires addressing the problem of temporal correspondence between the frames of the sequence. We present a method for time-consistent editing of triangle mesh sequences with varying connectivity using sparse temporal correspondence, which can be obtained using existing methods. Our method includes a deformation model based on the usage of the sparse temporal correspondence, which is suitable for the temporal propagation of user-specified deformations of the edited surface with respect to the shape and true topology of the surface while preserving the individual connectivity of each frame. Since there is no other method capable of comparable types of editing on time-varying meshes, we compare our method and the proposed deformation model with a baseline approach and demonstrate the benefits of our framework.Item Accelerated multi-hillshade hierarchic clustering for automatic lineament extraction(2024) Kaas, Ondřej; Šilhavý, Jakub; Kolingerová, Ivana; Čada, VáclavThe lineaments are linear features reflecting mountain ridges or discontinuities in the geological structure. Recently, an automatic approach of their recognition based on multi-hillshade hierarchic clustering (MHHC) has been developed, based on line extraction from a raster image. This paper presents a modification of MHHC, which solves the spatial line segment clustering as a facility location problem. The proposed modification is faster than MHHC while not changing the method’s core.Item Improved Methodology for Assessment of Communication Protocols for Distributed Road Traffic Simulation(2024) Potužák, TomášThis paper describes an improved methodology for testing and assessment of high-level communication protocols for micro-scale (or microscopic) distributed road traffic simulations. The methodology investigates the dependencies of the communication protocols’ performance on various features of the simulation and enables to easily calculate score for each of the tested protocols. Using the scores, the tested protocols can be directly compared. The improved version of the methodology is an evolution of its original version. It newly incorporates the assessment of the error introduced into the simulation by lossy communication protocols and reduces overall number of performed tests.Item Simplification of contour lines, based on axial splines, with high-quality results(2023) Bayer, Tomáš; Kolingerová, Ivana; Čelonk, Marek; Lysák, JakubThis paper introduces a new simplification method providing high-quality contour lines derived from the 3D point cloud. It combines the simplification potential and the splines with the generalized axial symmetry. It applies to large-scale maps (1:5000–1:25,000). It significantly improves all geometric and shape parameters of contour lines, namely in flatter areas. The simplified contour lines preserve the given vertical error, lie within the vertical buffer, are aesthetically pleasing, and have similar spacing; their artificial oscillations are significantly reduced.Item An incremental facility location clustering with a new hybrid constrained pseudometric(2023) Bayer, Tomáš; Kolingerová, Ivana; Potůčková, Markéta; Čábelka, Miroslav; Štefanová, EvaThe Euclidean metric, one of the classical similarity measures applied in clustering algorithms, has drawbacks when applied to spatial clustering. The resulting clusters are spherical and similarly sized, and the edges of objects are considerably smoothed. This paper proposes a novel hybrid constrained pseudometric formed by the linear combination of the Euclidean metric and a pseudometric plus penalty. The pseudometric is used in a new deterministic incremental heuristic facility location algorithm (IHFL). Our method generates larger, isotropic, and partially overlapping clusters of different sizes and spatial densities, better adapting to the surface complexity than the classical non-deterministic clustering. Cluster properties are used to derive new features for supervised/unsupervised learning. Possible applications are the classification of point clouds, their simplification, detection, filtering, and extraction of different structural patterns or sampled objects. Experiments were run on point clouds derived from laser scanning and images.Item Model-Free-Communication Federated Learning: Framework and application to Precision Medicine(2024) De Falco, Ivan; Della Cioppa, Antonio; Koutný, Tomáš; Scafuri, Umberto; Tarantino, ErnestoThe problem of executing machine learning algorithms over data while complying with data privacy is highly relevant in many application areas, including medicine in general and Precision Medicine in particular. In this paper, an innovative framework for Federated Learning is proposed that allows performing machine learning and effectively tackling the issue of data privacy while taking a step towards security during communication. Unlike the standard federated approaches where models should travel on the communication networks and would be subject to possible cyberattacks, the models proposed by our framework do not need to travel, thus moving in the direction of security improvement. Another very appealing feature is that it can be used with any machine learning algorithm provided that, during the learning phase, the model updating does not depend on the input data. To show its effectiveness, the learning process is here accomplished by an Evolutionary Algorithm, namely Grammatical Evolution, thus also obtaining explicit knowledge that can be provided to the domain experts to justify the decisions made. As a test case, glucose values prediction for a number of patients with type 1 diabetes is considered and is tackled as a classification problem, the goal being to predict for any future value a possible range. Finally, a comparison of the performance of the proposed framework is performed against that of a non-Federated Learning approach.Item Cross-lingual aspect-based sentiment analysis: A survey on tasks, approaches, and challenges(2025) Šmíd, Jakub; Král, PavelAspect-based sentiment analysis (ABSA) is a fine-grained sentiment analysis task that focuses on understanding opinions at the aspect level, including sentiment towards specific aspect terms, categories, and opinions. While ABSA research has seen significant progress, much of the focus has been on monolingual settings. Cross-lingual ABSA, which aims to transfer knowledge from resource-rich languages (such as English) to low-resource languages, remains an under-explored area, with no systematic review of the field. This paper aims to fill that gap by providing a comprehensive survey of cross-lingual ABSA. We summarize key ABSA tasks, including aspect term extraction, aspect sentiment classification, and compound tasks involving multiple sentiment elements. Additionally, we review the datasets, modelling paradigms, and cross-lingual transfer methods used to solve these tasks. We also examine how existing work in monolingual and multilingual ABSA, as well as ABSA with LLMs, contributes to the development of cross-lingual ABSA. Finally, we highlight the main challenges and suggest directions for future research to advance cross-lingual ABSA systems.Item AhiLS - an Algorithm for Establishing Hierarchy among Detected Weak Local Reflection Symmetries in Raster Images(2024) Podgorolec, David; Kolingerová, Ivana; Lovenjak, Luka; Žalik, BorutA new algorithm is presented for detecting the local weak reflection symmetries in raster images. It uses contours extracted from the segmented image and a convex hull. A tree representing the hierarchy of the detected local symmetries is the result of the algorithm.Item A case study on entropy-aware block-based linear transforms for lossless image compression(2024) Žalik, Borut; Podgorolec, David; Kolingerová, Ivana; Strnad, Damjan; Kohek, ŠtefanData compression algorithms tend to reduce information entropy, which is crucial, especially in the case of images, as they are data intensive. In this regard, lossless image data compression is especially challenging. Many popular lossless compression methods incorporate predictions and various types of pixel transformations, in order to reduce the information entropy of an image. In this paper, a block optimisation programming framework is introduced to support various experiments on raster images, divided into blocks of pixels. Eleven methods were implemented, including prediction methods, string transformation methods, and inverse distance weighting, as a representative of interpolation methods.Item A New Transformation Technique for Reducing Information Entropy: A Case Study on Greyscale Raster Images(2023) Žalik, Borut; Strnad, Damjan; Podgorolec, David; Kolingerová, Ivana; Lukač, Luka; Lukač, Niko; Kolmanič, Simon; Žalik, Krista Rizman; Kohek, ŠtefanThis paper proposes a new string transformation technique called Move with Interleaving (MwI). Four possible ways of rearranging 2D raster images into 1D sequences of values are applied, including scan-line, left-right, strip-based, and Hilbert arrangements.Item A Novel Radial Basis Function Description of a Smooth Implicit Surface for Musculoskeletal Modelling(2024) Červenka, Martin; Kohout, Josef; Lipus, BogdanAs musculoskeletal illnesses continue to increase, practical computerised muscle modelling is crucial. This paper addresses this concern by proposing a mathematical model for a dynamic 3D geometrical surface representation of muscles using a Radial Basis Function (RBF) approximation technique. The objective is to obtain a smoother surface while minimising data use, contrasting it from classical polygonal (e.g. triangular) surface mesh models or volumetric (e.g. tetrahedral) mesh models. The paper uses RBF implicit surface description to describe static surface generation and dynamic surface deformations based on its spatial curvature preservation during the deformation. The novel method is tested on multiple data sets, and the experiments show promising results according to the introduced metrics.
