• Journal of the Korea Computer Graphics Society
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• v.24 no.3
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• pp.33-41
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• 2018

We present a secondary camera optimization method that helps the user exploring 3D virtual environment to precisely observe possible collisions between objects. The first role of our secondary camera is to automatically detect the area with the greatest possible collision. The second role is to show the detected area from a new angle of view that the current main camera cannot show. However, as the shapes of target objects are complex, the shape of the empty space between objects is also complex and narrow. It means that the space for the secondary camera position is highly constrained and its optimization can be very difficult. To avoid this difficulty and increase the efficiency of the optimization, we first compute a bisector surface between two target objects. Then, we limit the domain of the secondary camera's position on the bisector surface in the optimization process. To verify the utility of our method, we built a demonstration program in which the user can explore in a 3D virtual world and interact with objects by using a hand motion recognition device and conducted a user study.

• International Journal of CAD/CAM
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• v.8 no.1
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• pp.11-20
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• 2009

The conventional methods of boundary-conformed 2D surfaces generation usually yield some problems. This paper deals with two boundary-conformed 2D surface generation methods, one conventional approach, the linear Coons method, and a new method, boundary-conformed interpolation. In this new method, unidirectional 2D surface has been generated using some of the geometric properties of the given boundary curves. A method of simultaneous displacement of the interpolated curves from the opposite boundaries has been adopted. The geometric properties considered for displacements include weighted combination of angle bisector and linear displacement vectors at all the data-points of the two opposite generating curves. The algorithm has one adjustable parameter that controls the characteristics of transformation of one set of curves from its parents. This unidirectional process has been extended to bi-directional parameterization by superimposing two sets of unidirectional curves generated from both boundary pairs. Case studies show that this algorithm gives reasonably smooth transformation of the boundaries. This algorithm is more robust than the linear Coons method and capable of resolving the 2D boundary-conformed parameterization problems.

• Journal of Korean society of Dental Hygiene
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• v.12 no.5
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• pp.987-997
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• 2012

Objectives : This study was carried out in order to obtain basic data for students' efficient acquirement and instruction of radiography technology in the future by surveying dental hygiene students' recognition of periapical radiography. Methods : This study carried out a questionnaire survey targeting dental hygiene students from December 2009 to December 2010, and obtained the following results. Results : 1. As a result of examining recognition on periapical radiography, the bisecting angle technique was indicated to be averagely $3.84{\pm}0.566$ points. The paralleling technique was indicated to be $2.66{\pm}0.701$ points. 2. As a result of examining about problems given the bisecting angle technique, what had been most difficult given the bisecting angle technique was indicated to be the highest in cone positioning with 34.2%. The most difficulty given deciding on the X-ray vertical-angel irradiation direction was indicated to be the highest with 66.9% in adjusting the cone direction on the virtual bisector. 3. As a result of examining about problems given the paralleling technique, what had been most difficult in the process of the paralleling technique was indicated to be the highest with 56.7% in fixing the film immobilization device inside the mouth. Conclusions : Examining the above results, it is considered that there is a need of understanding morphological and anatomical structure inside the mouth in order to reduce the mistake rate given the periapical radiography, and that it is important to increase skill level by repetitively shooting several times with having enough time.

• Wind and Structures
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• v.5 no.1
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• pp.25-48
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• 2002

Wind flow and pressure on the roof of the Texas Tech Experimental Building are studied along with the incident wind in an effort to understand the wind-structure interaction and the mechanisms of roof pressure generation. Two distinct flow phenomena, cornering vortices and separation bubble, are investigated. It is found for the cornering vortices that the incident wind angle that favors formation of strong vortices is bounded in a range of approximately 50 degrees symmetrical about the roof-corner bisector. Peak pressures on the roof corner are produced by wind gusts approaching at wind angles conducive to strong vortex formation. A simple analytical model is established to predict fluctuating pressure coefficients on the leading roof corner from the knowledge of the mean pressure coefficients and the incident wind. For the separation bubble situation, the mean structure of the separation bubble is established. The role of incident wind turbulence in pressure-generation mechanisms for the two flow phenomena is better understood.