• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1305-1313
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• 2013

In this study, a method to apply feature-based simplification to boundary representation models is proposed. For feature-based simplification, a volume decomposition tree is created from a boundary representation model. The volume decomposition tree is represented by regularized Boolean operations of additive volumes, subtractive volumes, and fillet/round/chamfer volumes, and it is generated by stepwise volume decomposition, which consists of fillet/round/chamfer decomposition, wrap-around decomposition, volume split decomposition, and cell-based decomposition. After the volume decomposition tree is transformed to an infix expression, the CAD model can be simplified by reordering the volumes. To verify the proposed method, a prototype system was implemented, and experiments on test cases were conducted. From the results of the experiments, it is verified that the proposed method is useful for simplifying CAD models based on boundary representation.

• Journal of the Korea Computer Graphics Society
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• v.20 no.4
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• pp.1-7
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• 2014

The volume rendering has become an important technique in many applications along with hardware development. Understanding and perception of volume visualization benefit from visual cues which are available from shading. Better visual cues can be obtained from global illumination models but it's huge amount of computation and extra GPU memory need cause a lack of interactivity. In this paper, in order to improve visual cues on volume rendering, we propose an image space occlusion shading model which requires no additional resources.

• Journal of the Korea Computer Graphics Society
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• v.6 no.1
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• pp.19-27
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• 2000

This paper proposes a non-self-intersecting multiresolution deformable model to extract and reconstruct three-dimensional boundaries of objects from volumetric data. Deformable models offer an attractive method for extracting and reconstructing the boundary surfaces. However, convensional deformable models have three limitations- sensitivity to model initialization, difficulties in dealing with severe object concavities, and model self-intersections. We address the initialization problem by multiresolution model representation, which progressively refines the deformable model based on multiresolution volumetric data in order to extract the boundaries of the objects in a coarse-to-fine fashion. The concavity problem is addressed by mesh size regularization, which matches its size to the unit voxel of the volumetric data. We solve the model self-intersection problem by including a non-self-intersecting force among the customary internal and external forces in the physics-based formulation. This paper presents results of applying our new deformable model to extracting a sphere surface with concavities from a computer-generated volume data and a brain cortical surface from a MR volume data.

• Journal of the Korea Computer Graphics Society
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• v.21 no.5
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• pp.37-44
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• 2015

This paper presents a novel 3D model representation, called hybrid model representation, to overcome existing 3D volume-based indoor scene reconstruction mechanism. In indoor 3D scene reconstruction, volume-based model representation can reconstruct detailed 3D model for the narrow scene. However it cannot reconstruct large-scale indoor scene due to its memory consumption. This paper presents a memory efficient plane-hash model representation to enlarge the scalability of the indoor scene reconstruction. Also, the proposed method uses plane-hash model representation to reconstruct large, structural planar objects, and at the same time it uses volume-based model representation to recover small detailed region. Proposed method can be implemented in GPU to accelerate the computation and reconstruct the indoor scene in real-time.

• The Journal of the Korea Contents Association
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• v.10 no.4
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• pp.106-114
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• 2010

Mesh parameterization is the process of finding one-to-one mapping between an input mesh and a parametric domain. It has been considered as a fundamental tool for digital geometric processing which is required to develop several applications of digital geometries. In this paper, we propose a novel 3D volume parameterization by means that a harmonic mapping is established between a 3D volume mesh and a unit solid cube. To do that, we firstly partition the boundary of the given 3D volume mesh into the six different rectangular patches whose adjacencies are topologically identical to those of a surface cube. Based on the partitioning result, we compute the boundary condition as a precondition for computing a volume mesh parameterization. Finally, the volume mesh parameterization with a low-distortion can be accomplished by performing a harmonic mapping, which minimizes the harmonic energy, with satisfying the boundary condition. Experimental results show that our method is efficient enough to compute 3D volume mesh parameterization for several models, each of whose topology is identical to a solid sphere.

• 한국HCI학회:학술대회논문집
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• 2009.02a
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• pp.68-73
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• 2009

As various haptic algorithms and haptic equipments have developed, the computer simulation includes the haptic simulation. Basically, the haptic simulation requires very fast refresh rate approximately 1000 Hz. The traditional haptic simulations have satisfied that requirement by simplifying the target model. In soft body simulation, simplifying the deformation is not good because the visual feedback is important. Separating haptic model from deformable model can be solution of that problem. However, the user may feel a subtle distiction because the relationship between two models are not clear. In this paper, we propose the hybrid model to manipulate haptic rendering and deformation and define the relationship between two models.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10b
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• pp.499-501
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• 2000

음함수 곡면 모델의 대표적인 구조 요소인 메타볼은 다양한 형태의 곡면을 모델링하는데 뛰어난 성능을 갖는다[1]. 그러나 복잡한 형태의 물체는 곡면 뿐 아니라 평면적인 요소를 포함하기 때문에 메타볼만으로 부정형 물체를 모델링하는 데에는 많은 어려움이 따른다. 메타큐브는 메타볼의 장점을 수용하면서 적은 수의 데이터로 평면 형태의 물체가지 모델링할 수 있는 메타볼의 확장 형태로서, 두 개의 매개변수만으로 구에서 정육면체까지 자유로운 확장이 가능하다[2]. 본 논문은 메타큐브를 이용하여 볼륨 데이터로부터 3차원 물체를 자동 모델링하는 방법을 제안한다. 제안 방법은 볼륨 데이터의 형태에 기반하여 분할된 볼륨 트리를 이용하여 비교적 빠른 시간에 볼륨 데이터로부터 비슷한 형태의 3차원 물체를 재구성하는 메타큐브 집합을 추출한다. 다양한 볼륨데이타에 대한 실험 결과를 제시함으로써 제안 방법의 효용성을 증명한다.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.11
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• pp.589-600
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• 2002

Deformable models offer an attractive approach for extracting three-dimensional boundary structures from volumetric images. However, conventional deformable models have three major limitations - sensitive to initial condition, difficult to represent complex boundaries with severe object concavities and protrusions, and self-intersective between model elements. This paper proposes a deformable model that is effective to extract geometrically complex boundary surfaces by improving away the limitations of conventional deformable models. First, the proposed deformable model resamples its elements hierarchically based on volume image pyramid. The hierarchical resampling overcomes sensitivity to initialization by extracting the boundaries of objects in a multiscale scheme and enhances geometric flexibility to be well adapted to complex image features by refining and regularizing the size of model elements based on voxel size. Second, the physics-based formulation of our model integrates conventional internal and external forces, as well as a non-self-intersecting force. The non-self-intersecting force effectively prevents collision or crossing over between non-neighboring model elements by pushing each other apart if they are closer than a limited distance. We show that the proposed model successively extracts the complex boundaries including severe concavities and protrusions, neither depending on initial position nor causing self-intersection, through the experiments on several computer-generated volume images and brain MR volume images.

• The Journal of Korean Institute of Next Generation Computing
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• v.15 no.5
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• pp.75-83
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• 2019

Direct volume rendering is a widely used method for visualizing three-dimensional volume data such as medical images. This paper proposes a method for applying depth-of-field effects to volume ray-casting to enable more realistic depth-of-filed rendering in direct volume rendering. The proposed method exploits a camera model based on the human perceptual model and can obtain realistic images with a limited number of rays using jittered lens sampling. It also enables interactive exploration of volume data by on-the-fly calculating depth-of-field in the GPU pipeline without preprocessing. In the experiment with various data including medical images, we demonstrated that depth-of-field images with better depth perception were generated 2.6 to 4 times faster than the conventional method.

• Proceedings of the Korea Information Processing Society Conference
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• 2016.04a
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• pp.751-753
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• 2016

볼륨 렌더링에서 가시화된 물체를 더욱 사실적으로 표현하기 위해서는 조명효과의 표현이 중요하다. 이를 위해 빛의 직접적인 영향과, 산란, 흡수에 따른 소멸, 반사등을 고려하여 빛의 에너지를 누적시켜 표현한다. 이러한 모든 연산을 수행하려면 많은 자원과 연산이 필요 하기 때문에, 여러 근사 방법들이 제안 되어 왔다. 본 논문에서는 3 차원 정보를 갖는 템플릿을 통해 광원의 위치에 상관없이 산란효과와 음영 효과를 표현한다. 램버트의 조명 모델을 기반으로 볼륨 데이터 전체에 대한 광원맵이 아닌 물체의 성질로부터 적은 자원을 차지하는 빛 분포-템플릿들을 생성한다. 생성된 템플릿들을 빛의 영향에 따라 누적 계산하여 3차원 볼륨 데이터를 가시화하는 방법을 제안한다.