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Content available remote A robust technique for surface reconstruction from orthogonal slices
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Sviták R. , Skala V.
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tom Vol. 13, No. 3
221-233
EN
The problem of surface reconstruction from sets of planar slices representing cross sections through 3D objects is presented. The final result of surface reconstruction is always based on the correct estimation of the structure of the original object and on the visual quality of the resultant surface. This paper is a case study of the structure reconstruction and the surface formation problems. We present a new approach, which is based on considering mutually orthogonal sets of slices. A new method for surface reconstruction from orthogonal slices is described, and the benefit of orthogonal slices is also discussed. The properties and sample results are presented as well. Key words: surface reconstruction, orthogonal slices, orthogonal cross-sections, contour correspondence.
2
Content available remote A comparison of fundamental methods for iso surface extraction
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Patera J. , Skala V.
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tom Vol. 13, No. 4
329-343
EN
This paper compares four fundamental methods for iso surface extraction based on cell decomposition to tetrahedra. The methods are compared both on mathematically generated data sets as well as on real data sets. The comparison using mathematical data is made from different points of view such, as area approximation, or volume approximation. On the other hand, the Hausdorff distance and the root mean square are used to compare methods on real data sets. The presented comparison can be of help when deciding which of the tested methods to choose, as well as when we need to compare a newly developed method with other existing approaches.
3
Content available remote Two new algorithms for line clipping in E² and their comparison
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Skala V. , Hui B. D.
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tom Vol. 9, No. 1/2
297-306
EN
New efficient algorithms for the line clipping by the given rectangle in E² are presented. The first algoritm is based on the line direction evaluation the second one is based on a new coding technique of clipping rectangle's vertices. It allows solving all cases more effectively. A comparison of the proposed algorithms with the Liang-Barsky algorithm and some experimental results are presented, too.
4
Content available remote Two methods for iso-surface extraction from vlumetric data and their comparison
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Skala V. , Brusi A.
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tom Vol. 9, No. 1/2
149-166
EN
There are various methods for extracting iso-surfaces from volumetric data. Marching cubes or tetrahedra or raytracing methods are mostly used. There are many specific techniques to increase speed of computation and decrease memory requirements. Although a precision of iso-surface extraction is very important, too, it is not mentioned usually. A comparison of the selected method was made in different aspects: iso-surface extraction process time, number of triangles generated and estimation of radius, area and volume errors based on approximation of a sphere. Surprisingly, experiments proved that there is no direct relation between precision of extracted and human perception of the extracted iso-surface.
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Content available remote Faster algorithm for line clipping against a pyramid in E³
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Skala V. , Bui D. H.
Machine Graphics and Vision
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2000
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tom Vol. 9, No. 4
841-850
EN
A new algorithm for line clipping against a pyramid in E³ is presented. The suggested algorithm is based on the use of a separation function and avoids conmputation of intersection points that are not endpoints of the output line segment. It also allows to solved all cases more effictively. The performance of this algorithm is shown to be consistently better than the traditional Liang-Barsky's algorithm for line clipping in E³. Experimental are also presented.
6
Content available On streamwise structures in boundary layer under adverse pressure gradient on inclined plate
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Uruba V. , Prochazka P. , Skala V.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2018
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tom Vol. 22, No 3
255--267
EN
The presented study is focused on experimental investigation of a boundary layer on a flat plate in an adverse pressure gradient. The flat plate is placed in a regular flow, the pressure gradient is generated by the plate inclination. The preceding studies deal with the structure of the wake behind the plate, the presented study concentrates on the flow structureclose to the suction surface of the plate. The dynamical behavior of the flow structures is studied in details with respect to the topology in the streamwise direction. In spite of the fact that thetime-mean flow field is close to 2D, more or less constant along the span, the instantaneous structures topology is fully 3D. Rather oblique structures are detected instead of those oriented in the streamwise direction. The patterns are travelling in the streamwise direction along the plate.
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