• Journal of Korea Multimedia Society
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• v.15 no.3
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• pp.398-407
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• 2012

We propose a tree modeling method of expressing realistically and efficiently numerous trees distributed on a broad terrain. This method combines and simplifies the recursive hierarchy of tree branch and branch generation process through self-organizing from buds, allowing users to generate trees that can be used more intuitively and efficiently. With the generation process the leveled structure and the appearance such as branch length, distribution and direction can be controlled interactively by user. In addition, we introduce an environment-adaptive model that allows to grow a number of trees variously by controlling at the same time and we propose an efficient application method of growing environment. For the real-time rendering of the complex tree models distributed on a broad terrain, the rendering process, the LOD(level of detail) for the branch surfaces, and shader instancing are introduced through the GPU(Graphics Processing Unit). Whether the numerous trees are expressed realistically and efficiently on wide terrain by proposed models are confirmed through simulation.

• Journal of Digital Contents Society
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• v.16 no.2
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• pp.189-196
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• 2015

The proposed cooperative 3D modelling system enables more efficient modeling works by improving current cooperation systems. Current 3D modeling tasks work on off-line and most of works are cooperation systems which communicate by files. These cooperation system cannot be interactive, occurs time delay while feedback and must have some programs which can read the files. This paper solves these problems using web that has the characteristics of network and proposes new cooperation system form. Using WebGL(Web Graphics Library) which is proposing technology in technical realization of Web 3D modeling, we make 3D objects in web browser and these objects can be manipulated by server-client communication. Therefore, if people use this system, they can use real time interaction and feedback. Also this system lowers a software installation necessity and can access everytime if web browser is installed.

• Journal of the Korea Computer Graphics Society
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• v.23 no.5
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• pp.29-38
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• 2017

We propose a method for tree-inspired chair modeling that can generate a tree-branch pattern in the skeleton of an arbitrary chair shape. Unlike existing methods that merge multiple-input models, the proposed method requires only one mesh as input, namely the contour mesh of the user's desired part, to model the chair with a branch pattern generated by tree-growth simulation. We propose a new method for the efficient extraction of the contour-mesh region in the tree-branch pattern. First, we extract the contour mesh based on the face area of the input mesh. We then use the front and back mesh information to generate a skeleton mesh that reconstructs the connection information. In addition, to obtain the tree-branch pattern matching the shape of the input model, we propose a three-way tree-growth simulation method that considers the tangent vector of the shape surface. The proposed method reveals a new type of furniture modeling by using an existing furniture model and simple parameter values to model tree branches shaped appropriately for the input model skeleton. Our experiments demonstrate the performance and effectiveness of the proposed method.

• Journal of the Korea Computer Graphics Society
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• v.18 no.1
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• pp.1-9
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• 2012

Video-based modeling / rendering developed to produce photo-realistic video contents have been one of the important research topics in computer graphics and computer visions. To smoothly combine original input video clips and 3D graphic models, geometrical information of light sources and cameras used to capture a scene in the real world is essentially required. In this paper, we present a simple technique to estimate the position and orientation of an optimal light source from the topology of objects and the silhouettes of shadows appeared in the original video clips. The technique supports functions to generate well matched shadows as well as to render the inserted models by applying the estimated light sources. Shadows are known as an important visual cue that empirically indicates the relative location of objects in the 3D space. Thus our method can enhance realism in the final composed videos through the proposed shadow generation and rendering algorithms in real-time.

• Journal of the Korea Computer Graphics Society
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• v.17 no.1
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• pp.1-7
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• 2011

We present a new technique for constructing a sweep surface using two-parameter motion. Firstly, a new rational B-spline motion with two parameters is introduced, which is obtained by extending its orientation curve and scaling curve to surface counterparts. A sweep surface is then defined by a single vertex v under the two-parameter motion and allows to represent different u-directional iso-curves depending on parameter ${\upsilon}$. Efficient techniques for modeling and editing the surface are achieved by intuitively controlling the two-parameter motion. We demonstrate the effectiveness of our technique with experimental results on modeling and editing a 3D propeller model.

• Journal of the Korea Computer Graphics Society
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• v.4 no.1
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• pp.55-66
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• 1998

This paper presents a simple method for relieving the ambiguity problems within the sub-voxel based surface-fitting approach for the surface construction. ECB algorithm is proposed to avoid the ambiguity problem which is the root of the holes within the resulting polygon based approximation. The basic idea of our disambiguation strategy is the use of a set of predefined modeling primitives (we call SMP) which guarantees the topological consistency of resulted surface polygons. 20 SMPs are derived from the extension of the concept of the elementary modeling primitives in the CB algorithm [3], and fit one to five faces of them to the iso-surface crossing a cell with no further processing. A look-up table which has a surface triangle list is pre-calculated using these 20 SMPs. All of surface triangles in the table are from the faces of SMPs and are stored in the form of edge list on which vertices of each surface triangle are located. The resulted polygon based approximation is unique at every threshold value and its validity is guaranteed without considering the complicated problems such as average of density and postprocessing. ECB algorithm could be free from the need for the time consuming post-processing, which eliminates holes by revisiting every boundary cell. Through three experiments of surface construction from volume data, its capability of hole avoidance is showed.

• Journal of the Korea Computer Graphics Society
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• v.8 no.4
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• pp.1-7
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• 2002

This paper presents a new approach for modeling human limbs shape from 3D scan data. Based on the cylindrical structure of limbs, the overall shape is approximated with a set of ellipsoids through ellipsoid fitting and interpolation of fit-ellipsoids. Then, the smooth domain surface representing the coarse shape is generated as the envelope surface of ellipsoidal sweep, and the fine details are reconstructed by constructing parametric displacement function on the domain surface. For fast calculation, the envelope surface is approximated with ellipse sweep surface, and points on the reconstructed surface are mapped onto the corresponding ellipsoid. We demonstrate the effectiveness of our approach for skeleton-driven body deformation.

• Journal of the Korea Computer Graphics Society
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• v.10 no.2
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• pp.1-9
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• 2004

본 논문에서는 바이러스와 같은 생화학 물질의 분자구조를 3 차원 모델로 시각화하여 관찰하고, 그 분자모델을 직관적인 방법으로 조작하기 위한 가상 현실 분자 모델링 시스템을 제안한다. 이 시스템을 사용하면, 입체영상 디스플레이 장치와 데이터 글러브 및 동작 추적 장치를 사용하여 3 차원 분자 모델을 실감나게 조작할 수 있어서 효율적으로 분자들을 관찰하고 결합, 분리하는 등의 분자 모델링 작업이 가능하다. 사용자들은 마우스나 키보드 등의 장비 대신에 자연스러운 몸 동작이나 손 동작을 이용하여 분자 모델링 작업을 위한 동작을 하게 된다. 분자들의 결합을 화학적으로 정확하게, 그리고 실시간으로 시뮬레이션 하기 위해서 에너지 계산 알고리즘을 구현하였으며 이러한 작업이 가능하도록 분자 구조를 표현하는 새로운 자료구조를 제안하였다. 본 연구에서 제안하는 동작 기반의 VR 분자 모델링 시스템의 타당성을 검증하기 위하여 HIV 바이러스 분자를 가지고 분자 모델링 작업을 수행하였고, 사용자 테스트를 실시하여 기존의 방식과 작업 성능 및 사용자 만족도를 비교하였다.

• International Journal of CAD/CAM
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• v.6 no.1
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• pp.139-148
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• 2006

Catmull-Clark subdivision scheme provides a powerful method for building smooth and complex surfaces. But the number of faces in the uniformly refined meshes increases exponentially with respect to subdivision depth. Adaptive tessellation reduces the number of faces needed to yield a smooth approximation to the limit surface and, consequently, makes the rendering process more efficient. In this paper, we present a new adaptive tessellation method for general Catmull-Clark subdivision surfaces. Different from previous control mesh refinement based approaches, which generate approximate meshes that usually do not interpolate the limit surface, the new method is based on direct evaluation of the limit surface to generate an inscribed polyhedron of the limit surface. With explicit evaluation of general Catmull-Clark subdivision surfaces becoming available, the new adaptive tessellation method can precisely measure error for every point of the limit surface. Hence, it has complete control of the accuracy of the tessellation result. Cracks are avoided by using a recursive color marking process to ensure that adjacent patches or subpatches use the same limit surface points in the construction of the shared boundary. The new method performs limit surface evaluation only at points that are needed for the final rendering process. Therefore it is very fast and memory efficient. The new method is presented for the general Catmull-Clark subdivision scheme. But it can be used for any subdivision scheme that has an explicit evaluation method for its limit surface.

• Journal of the Korea Computer Graphics Society
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• v.18 no.2
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• pp.63-72
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• 2012

As BIM(Building Information Modeling) is widely used in the construction process the need for exploring building models realistically is also growing. In this paper, we present a 3D stereoscopic navigation method for virtual buildings considering virtual perception. We first find out factors that may cause virtual discomfort while navigating stereoscopic building models, and then develop a method for automatically adjusting the range of virtual camera separation. In addition, we measure each user's JND(Just Noticeable Difference) in depth to adjust virtual camera separation and movement. The presented method can be used for various architectural applications by creating user-customized 3D stereoscopic contents.