• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.50.1-50.1
• /
• 2015

We present a new hydrodynamic simulation based on the unstructured moving mesh scheme. The simulation utilizes the Voronoi tessellation technique that produces polygonal cells composed of, on average, 13 surfaces each in 3D. We devise the incremental expanding method (IEM) and hybrid-neighbor searching algorithm and achieve the CPU time just proportional to the number of particles, i.e., O(N). We show the results of requisite tests for hydrodynamic simulations and demonstrate superiority of our code over the conventional codes using the stationary meshes. The applications in the context of cosmological and galactic simulations are also discussed.

• Proceedings of the Korean Information Science Society Conference
• /
• 2003.04a
• /
• pp.824-826
• /
• 2003

지능형 개념기반 검색시스템(Intelligent Concept Based Retrieval System)은 구문적 서술(Syntactic Description)과 의미적 서술(Semantic Description)과 의한 상호 융합으로 이뤄질 수 있는데 컬러 히스토그램, Curvanature 히스토그램등과 같은 구운적 서술(Syntactic Description) 내용의 추출은 현재의 기술들로 잘 이를 수 있다. 또한 특정 응용 분야에서뿐만 아니라 미디어 타입에 따라서도 쉽게 사용될 수 있다. 이미 MPEG-7에서 표준화된 Description Scheme을 제공하고 있다. 그러나 기술 구조 레벨과 개요 레벨등과 같은 다양한 기술 레벨들에 의해 구문적 서술(Syntactic Description) 이질성은 발생한다. 따라서 본 연구에서는 Polygonal mesh 기반 미디어 객체 표현방법을 제시하고 이를 통해 간접적 서술 변환을 할 수 있는 방안을 제시하여 구문적 서술(Syntactic Description)에서의 이질성 문제를 해결하였다.

• Journal of KIISE:Computer Systems and Theory
• /
• v.27 no.3
• /
• pp.245-254
• /
• 2000

This paper proposes a new discrete curvature error metric to generate LOD meshes. For mesh simplification, discrete curvatures are defined with geometric attributes, such as angles and areas of triangular polygonal model, and dihedral angles without any smooth approximation. They can represent characteristics of polygonal surface well. The new error metric based on them, discrete curvature error metric, increases the accuracy of simplified model by preserving the geometric information of original model and can be used as a global error metric. Also we suggest that LOD should be generated not by a simplification ratio but by an error metric. Because LOD means the degree of closeness between original and each level's simplified model. Therefore discrete curvature error metric needs relatively more computations than known other error metrics, but it can efficiently generate and control LOD meshes which preserve overall appearance of original shape and are recognizable explicitly with each level.

• Journal of KIISE:Computer Systems and Theory
• /
• v.29 no.6
• /
• pp.307-317
• /
• 2002

In this paper we propose a new mesh reconstruction scheme that produces a displaced subdivision surface directly from unorganized points. The displaced subdivision surface is a new mesh representation that defines a detailed mesh with a displacement map over a smooth domain surface, but original displaced subdivision surface algorithm needs an explicit polygonal mesh since it is not a mesh reconstruction algorithm but a mesh conversion (remeshing) algorithm. The main idea of our approach is that we sample surface detail from unorganized points without any topological information. For this, we predict a virtual triangular face from unorganized points for each sampling ray from a parameteric domain surface. Direct displaced subdivision surface reconstruction from unorganized points has much importance since the output of this algorithm has several important properties: It has compact mesh representation since most vertices can be represented by only a scalar value. Underlying structure of it is piecewise regular so it ran be easily transformed into a multiresolution mesh. Smoothness after mesh deformation is automatically preserved. We avoid time-consuming global energy optimization by employing the input data dependant mesh smoothing, so we can get a good quality displaced subdivision surface quickly.

• Journal of Korea Multimedia Society
• /
• v.9 no.11
• /
• pp.1483-1495
• /
• 2006

The navigation mesh represents a terrain as a set of triangles on which characters may move around. The navigation mesh cab be generated automatically, and it is more flexible in representing 3D surface. The number of triangles to represent a terrain may vary according to the structure of the terrain. As characters are moving around on a navigation mesh, the path planning can be performed more easily by projecting the 3D surfaces into 2D space. However, when the terrain is represented with an elaborated mesh of large number of triangles to achieve more realistic movements, the path finding can be very inefficient because there are too many states(triangles) to be searched. In this paper, we propose an efficient method of path finding in 3D games where the terrain is represented by navigation meshes. Our method uses the visibility tests. When the graph-based search is applied to elaborated polygonal meshes for detailed terrain representation, the path finding can be very inefficient because there are too many states(polygons) to be searched. In our method, we reduce the search space by using visibility tests so that the search can be fast even on the detailed terrain with large number of polygons. First we find the visible vertices of the obstacles, and define the heuristic function as the distance to the goal through those vertices. By doing that, the number of states that the graph-based search visits can be substantially reduced compared to the plane search with straight-line distance heuristic.

• Journal of KIISE:Computer Systems and Theory
• /
• v.31 no.5_6
• /
• pp.297-304
• /
• 2004

In this paper, a mesh simplification algorithm based on wavelet transform and 2D planar sampling is proposed for efficient handling of 3D objects in computer applications. Since 3D vertices are directly transformed with wavelets in conventional mesh compression and simplification algorithms, it is difficult to solve tiling optimization problems which reconnect vertices into faces in the synthesis stage highly demanding vertex connectivities. However, a 3D mesh is sampled onto 2D planes and 2D polygons on the planes are independently simplified in the proposed algorithm. Accordingly, the transform of 2D polygons is very tractable and their connection information Is replaced with a sequence of vertices. The vertex sequence of the 2D polygons on each plane is analyzed with wavelets and the transformed data are simplified by removing small wavelet coefficients which are not dominant in the subjective quality of its shape. Therefore, the proposed algorithm is able to change the mesh level-of-detail simply by controlling the distance of 2D sampling planes and the selective removal of wavelet coefficients. Experimental results show that the proposed algorithm is a simple and efficient simplification technique with less external distortion.

• Nuclear Engineering and Technology
• /
• v.49 no.7
• /
• pp.1495-1504
• /
• 2017

In a previous study, a set of polygon-mesh (PM)-based skin models including a $50-{\mu}m-thick$ radiosensitive target layer were constructed and used to calculate skin dose coefficients (DCs) for idealized external beams of electrons. The results showed that the calculated skin DCs were significantly different from the International Commission on Radiological Protection (ICRP) Publication 116 skin DCs calculated using voxel-type ICRP reference phantoms that do not include the thin target layer. The difference was as large as 7,700 times for electron energies less than 1 MeV, which raises a significant issue that should be addressed subsequently. In the present study, therefore, as an extension of the initial, previous study, skin DCs for three other particles (photons, protons, and helium ions) were calculated by using the PM-based skin models and the calculated values were compared with the ICRP-116 skin DCs. The analysis of our results showed that for the photon exposures, the calculated values were generally in good agreement with the ICRP-116 values. For the charged particles, by contrast, there was a significant difference between the PM-model-calculated skin DCs and the ICRP-116 values. Specifically, the ICRP-116 skin DCs were smaller than those calculated by the PM models-which is to say that they were under-estimated-by up to ~16 times for both protons and helium ions. These differences in skin dose also significantly affected the calculation of the effective dose (E) values, which is reasonable, considering that the skin dose is the major factor determining effective dose calculation for charged particles. The results of the current study generally show that the ICRP-116 DCs for skin dose and effective dose are not reliable for charged particles.

• Journal of the Korea Computer Graphics Society
• /
• v.13 no.1
• /
• pp.1-6
• /
• 2007

Although free-form surfaces can represent smooth shapes with only a few control points contrary to polygonal meshes, graphics hardware does not support surface rendering currently. Since modern programmable graphics pipeline can be used to accelerate various kinds of existing graphics algorithms, this paper presents a method that utilizes the graphics processing unit (GPU) to render blending surfaces with arbitrary topology fast. Surface parameters sampled on the control mesh and geometric data for local surfaces are sent to the graphics pipeline, and then the vertex processor evaluates the surface positions and normals with these data. This method can achieve very high performance rather than CPU-based rendering.

• Korean Journal of Optics and Photonics
• /
• v.20 no.2
• /
• pp.94-101
• /
• 2009

A novel method for the reconstruction of 3D shape and texture from elemental images has been proposed. Using this method, we can estimate a full 3D polygonal model of objects with seamless triangulation. But in the triangulation process, all the objects are stitched. This generates phantom surfaces that bridge depth discontinuities between different objects. To solve this problem we need to connect points only within a single object. We adopt a segmentation process to this end. The entire process of the proposed method is as follows. First, the central pixel of each elemental image is computed to extract spatial position of objects by correspondence analysis. Second, the object points of central pixels from neighboring elemental images are projected onto a specific elemental image. Then, the center sub-image is segmented and each object is labeled. We used the normalized cut algorithm for segmentation of the center sub-image. To enhance the speed of segmentation we applied the watershed algorithm before the normalized cut. Using the segmentation results, the subdivision process is applied to pixels only within the same objects. The refined grid is filtered with median and Gaussian filters to improve reconstruction quality. Finally, each vertex is connected and an object-based triangular mesh is formed. We conducted experiments using real objects and verified our proposed method.

• Journal of Korea Multimedia Society
• /
• v.5 no.4
• /
• pp.458-467
• /
• 2002

There has been proposed many simplification algorithms for effectively decreasing large-volumed polygonal surface data. These algorithms apply their own cost function for collapse to one of fundamental simplification unit, such as vertex, edge and triangle, and minimize the simplification error occurred in each simplification steps. Most of cost functions adopted in existing works use the error estimation method based on distance optimization. Unfortunately, it is hard to define the local characteristics of surface data using distance factor alone, which is basically scalar component. Therefore, the algorithms cannot preserve the characteristic features in surface areas with high curvature and, consequently, loss the detailed shape of original mesh in high simplification ratio. In this paper, we consider the vector component, such as surface orientation, as one of factors for cost function. The surface orientation is independent upon scalar component, distance value. This means that we can reconsider whether or not to preserve them as the amount of vector component, although they are elements with low scalar values. In addition, we develop a simplification algorithm based on half-edge collapse manner, which use the proposed cost function as the criterion for removing elements. In half-edge collapse, using one of endpoints in the edge represents a new vertex after collapse operation. The approach is memory efficient and effectively applicable to the rendering system requiring real-time transmission of large-volumed surface data.