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Abstract: A new algorithm is presented for detecting the global reflection symmetry of geometric objects. The algorithm works for 2D and 3D objects which may be open or closed and may or may not contain holes. The algorithm accepts a point cloud obtained by sampling the object’s surface at the input. The points are inserted into a uniform grid and so-called boundary cells are identified. The centroid of the boundary cells is determined, and a testing symmetry axis/plane is set through it. In this way, the boundary cells are split into two parts and they are faced with the symmetry estimation function. If the function estimates the symmetric case, the boundary cells are further split until a given threshold is reached or a non-symmetric result is obtained. The new testing axis/plane is then derived and tested by rotation around the centroid. This paper introduces three techniques to accelerate the computation. Competitive results were obtained when the algorithm was compared against the state of the art.
Keywords: computer science, computational geometry, uniform subdivision, centroids
Published in DKUM: 01.04.2025; Views: 0; Downloads: 4
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Abstract: Over the past 20 years, the first author and numerous collaborators have attempted to introduce computer-based laboratory exercises in science, particularly in biology classes. While working with secondary and post-secondary students, it was realised that it was possible to simultaneously develop cross-cutting competencies that bridged several key competences of the European framework of eight key competences for lifelong learning. These were (a) Collecting, analysing, and organising information; (b) Communication of ideas; (c) Planning and organising activities; (d) Working with others in teams; (e) The use of mathematical ideas and techniques; (f) Problem solving; and (g) The use of technology. When inquiry and problem-solving strategies are used, student achievement is much higher compared to explanatory and expository labs.
Keywords: biology education, computer based laboratory, key competences, laboratory work, science education
Published in DKUM: 25.09.2024; Views: 0; Downloads: 2
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Keywords: computer science, algorithms, computational geometry, computer vision, shape features
Published in DKUM: 23.08.2024; Views: 110; Downloads: 10
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Abstract: This 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. Experiments on 32 benchmark greyscale raster images of various resolutions demonstrated that the proposed transformation reduces information entropy to a similar extent as the combination of the Burrows–Wheeler transform followed by the Move-To-Front or the Inversion Frequencies. The proposed transformation MwI yields the best result among all the considered transformations when the Hilbert arrangement is applied.
Keywords: computer science, algorithm, string transformation, information entropy, Hilbert space filling curve
Published in DKUM: 22.05.2024; Views: 160; Downloads: 17
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Abstract: The paper presents a new algorithm for reflection symmetry detection, which is specialized to detect maximal symmetric patterns in an Earth observation (EO) dataset. First, we stress the particularities that make symmetry detection in EO data different from detection in other geometric sets. The EO data acquisition cannot provide exact pairs of symmetric elements and, therefore, the approximate symmetry must be addressed, which is accomplished by voxelization. Besides this, the EO data symmetric patterns in the top view usually contain the most useful information for further processing and, thus, it suffices to detect symmetries with vertical symmetry planes. The algorithm first extracts the so-called interesting voxels and then finds symmetric pairs of line segments, separately for each horizontal voxel slice. The results with the same symmetry plane are then merged, first in individual slices and then through all the slices. The detected maximal symmetric patterns represent the so-called partial symmetries, which can be further processed to identify global and local symmetries. LiDAR datasets of six urban and natural attractions in Slovenia of different scales and in different voxel resolutions were analyzed in this paper, demonstrating high detection speed and quality of solutions.
Keywords: computer science, approximate symmetry, partial symmetry, local symmetry, point cloud, voxel, line segment
Published in DKUM: 28.09.2023; Views: 438; Downloads: 37
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