• Mycobiology
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• v.32 no.1
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• pp.54-56
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• 2004

During the study of mushroom flora in Hongneung Arboretum, Ileodictyon gracile was confirmed as new to Korea and described based on morphological and microscopic characteristics in here. This species has subhypogeous, clathrate structure, and obovoid spores. The clathrate structures have $4{\sim}12$ polygonal meshes.

• International Journal of CAD/CAM
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• v.3 no.1_2
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• pp.77-83
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• 2003

We propose two algorithms to generate (1) polygonal meshes and (2) developable surface patches far generalized cylinders defined by contours of discrete curves. To solve the contour blending problem of generalized cylinder, the presented algorithms have adopted the algorithm and related properties of LIDM (linear interpolation by direction map) that interpolate geometric shapes based on direction map merging and group scaling operations. Proposed methods are fast to compute and easy to implement.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.15-19
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• 2001

A dedicated reverse engineering(RE) system for rapid manufacturing of human head in a 3D bust has been developed. The first step in the process is to capture the surface details of a human head and shoulder by three scanners based upon the digital moire fringe technique. Then the multiple scans captured from different angles are aligned and merged into a single polygonal mesh, and the aligned data set is refined by smoothing, subdividing or hole filling process. Finally, the refined data set is sent to a 4-axis computer numerically control(NC) machine to manufacture a replica. In this paper, we mainly describe on the algorithms and software for aligning multiple data sets. The method is based on the recently popular Iterative Closest Point(ICP) algorithm that aligns different polygonal meshes into one common coordinate system. The ICP algorithm finds the nearest positions on one scan to a collection of points on the other scan by minimizing the collective distance between different scans. We also integrate some heuristics into the ICP to enhance the aligning process. A typical example is presented to validate the system and further research work is also discussed.

• Journal of Electrical Engineering and Technology
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• v.6 no.6
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• pp.867-873
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• 2011

A navigation mesh (NavMesh) is a suitable tool for the representation of a three-dimensional game world. A NavMesh consists of convex polygons covering free space, so the path can be found reliably without detecting collision with obstacles. The main disadvantage of a NavMesh is the huge state space. When the $A^*$ algorithm is applied to polygonal meshes for detailed terrain representation, the pathfinding can be inefficient due to the many states to be searched. In this paper, we propose a method to reduce the number of states searched by using visibility tests to achieve fast searching even on a detailed terrain with a large number of polygons. Our algorithm finds the visible vertices of the obstacles from the critical states and uses the heuristic function of $A^*$, defined as the distance to the goal through such visible vertices. The results show that the number of searched states can be substantially reduced compared to the $A^*$ search with a straight-line distance heuristic.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.4
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• pp.140-147
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• 2004

In reverse engineering, the whole surfaces of the three-dimensional product are measured using 3D positional scanners. The raw triangle meshes constructed from a scanned point set are not well fitted for direct use in the downstream engineering or graphic activities. No object can be fully described by a single scan. Although multiple scans are usually taken and aligned to achieve a complete model, a set of scanned points does not entirely wrap the whole object. This is because some surfaces may be inaccessible to the scanner, so some portion of the scanned surface may be missing. This paper discusses the algorithms of a hole-filling that are crucial to refine the triangle meshes. In this paper, the holes are filled with flat triangles first by subdivision operation and then smoothed with neighboring triangles. This process continues until it converges to a certain user-defined iteration number. Examples are given and discussed to validate the system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.10
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• pp.4042-4059
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• 2020

The development of new multimedia techniques such as 3D printing is increasingly attracting the public's attention towards 3D objects. An optimized robust and imperceptible watermarking method based on Ant Colony Optimization (ACO) and Weber Law is proposed for 3D polygonal models. The proposed approach partitions the host model into smaller sub meshes and generates a secret watermark from the sub meshes using Weber Law. ACO based optimized strength factor is identified for embedding the watermark. The secret watermark is embedded and extracted on the wavelet domain. The proposed scheme is robust against geometric and photometric attacks that overcomes the synchronization problem and authenticates the secret watermark from the distorted models. The primary characteristic of the proposed system is the flexibility achieved in data embedding capacity due to the optimized strength factor. Extensive simulation results shows enhanced performance of the recommended framework and robustness towards the most common attacks like geometric transformations, noise, cropping, mesh smoothening, and the combination of such attacks.

• Korean Journal of Computational Design and Engineering
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• v.17 no.6
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• pp.436-442
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• 2012

Traumatic loading during car accidents or sports activities can lead to cervical spinal cord injury. Experiments in spinal cord injury research are mainly carried out on rabbit or rat. Finite element models that include the rat cervical spinal cord and adjacent soft tissues should be developed for efficient studies of mechanisms of spinal cord injury. Images of a rat were obtained from high resolution MRI scanner. Polygonal surfaces were extracted structure by structure from the MRI data using the ITK-SNAP volume segmentation software. These surfaces were converted to Non-uniform Rational B-spline surfaces by the INUS Rapidform rapid prototyping software. Rapidform was also used to generate a thin shell surface model for the dura mater which sheathes the spinal cord. Altair's Hypermesh pre-processor was used to generate finite element meshes for each structure. These processes in this study can be utilized in modeling of other biomedical tissues and can be one of examples for reverse engineering on biomechanics.

• Transactions of Materials Processing
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• v.16 no.7
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• pp.538-548
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• 2007

In this paper, a novel approach which enables rapid die surface modification for sheet metal forming process is proposed. In this method an implicit surface which interpolates a given set of control points and displacement constraints is generated to compute the displacements at arbitrary points located on die surface. The proposed method does not depend on the underlying surface representation type and is affected neither by its complexity nor by its quality. In addition, the domain decomposition method is introduced in order to treat large surface model. The global domain of interest is divided into smaller domains where the problem can be solved locally. And then the local solutions are combined together to obtain a global solution. In order to verify the validity and effectiveness of the proposed method, various surface modifications are carried out fur three kinds of die surface model including polygonal surface composed of triangular and rectangular meshes, polynomial surface and NURBS surface.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.12
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• pp.2374-2391
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• 2011

A variety of reconstruction methods has been developed to convert a set of scattered points generated from real models into explicit forms, such as polygonal meshes, parametric or implicit surfaces. In this paper, we present a method to construct multi-scale implicit surfaces from scattered points using multiscale kernels based on kernel and multi-resolution analysis theories. Our approach differs from other methods in that multi-scale reconstruction can be done without additional manipulation on input data, calculated functions support level of detail representation, and it can be naturally expanded for n-dimensional data. The method also works well with point-sets that are noisy or not uniformly distributed. We show features and performances of the proposed method via experimental results for various data sets.

• Journal of the Korea Computer Graphics Society
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• v.11 no.1
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• pp.21-30
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• 2005

그래픽, 오디오, 텍스트 정보 등의 저작권 보호를 위해 사용되어오던 디지털 워터마킹은 이제 기하 정보의 저작권을 보호하는데에도 중요하게 쓰이게 되었다. 스펙트랄 영역에서의 다각형 모델에 대한 워터마킹은 여러가지 공격에 대하여 강건함을 갖는다. 우리는 기존의 스펙트랄 영역에서의 워터마킹 기법을 일반화하고 이에 기반한 새로운 방법을 제시한다. 워터마크를 삽입 할 때에 라플라시안 행렬의 고유값과 고유벡터를 찾지 않는다. 대신 스케일링 함수로 부터 얻어진 선형 작용소를 사용한다. 테스트 결과는 서로 상충되는 워터마크를 삽입하고 추출하는데 드는 비용과 공격에 대한 강건성을 어떻게 조정하였는지 보여준다.