• Bulletin of the Korean Mathematical Society
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• v.44 no.3
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• pp.483-492
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• 2007

In this paper, we study the map projections from pseudo-sphere $S_1^2$ onto the non-lightlike surfaces in the 3-dimensional Lorentzian space, $L^3$, with curvature zero. We show geometrical means and properties of $\mathbb{R}{\times}S_1^1-cylindrical$, $S^1{\times}L-cylindrical$ and $\mathbb{R}{\times}H_0^1-cylindrical$ projections defined on $S_1^2$ to cylinders $\mathbb{R}{\times}S_1^1,\;S^1{\times}L$ and $\mathbb{R}{\times}H_0^1$, respectively, and orthographic and stereographic projections on $S_1^2$ to Lorentzian plane, $L^2$.

• The korean journal of orthodontics
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• v.45 no.6
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• pp.282-288
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• 2015

Objective: This study investigated whether it is possible to use a two-dimensional (2D) standard in three-dimensional (3D) analysis, by comparing the angles and lengths measured from a midsagittal projection in 3D cone-beam computed tomography (CBCT) with those measured by 2D lateral cephalometric radiography (LCR). Methods: Fifty patients who underwent both LCR and CBCT were selected as subjects. CBCT was reoriented in 3 different methods and the measuring-points were projected onto the midsagittal plane. Twelve angle values and 8 length values were measured on both LCR and CBCT and compared. Results: Repeated measures analysis of the variance revealed statistically significant differences in 7 angular and 5 linear measurements among LCR and 3 types of CBCT (p < 0.05). Of these 12 measurements, multiple comparisons showed that 6 measurements (ANB, AB to FH, IMPA, FMA, Co-Gn, Go-Me) were not significantly different in pairwise comparisons. LCR was significantly different from 3 types of CBCT in 3 angular (SN to FH, interincisal angle, FMIA) and 2 linear (S-Go, Co-ANS) measurements. The CBCT method was similar for all measurements, except for 1 linear measurement, i.e., S-N. However, the disparity between the mean values for all parameters was within the range of clinical measurement error. Conclusions: 3D-CBCT analysis, using midsagittal projection, is a useful method in which the 2D-LCR normative values can be used. Although the measurements changed with reorientation, these changes were not clinically significant.

• Korean Journal of Applied Biomechanics
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• v.17 no.2
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• pp.157-166
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• 2007

This study was to compare the major kinematic factors between the success and failure group on performing the back somersault motion in floor exercise. Three gymnasts(height : $167.3{\pm}2.88cm$, age : $22.0{\pm}1.0years$, body weight : $64.4{\pm}2.3kg$) were participated in this study. The kinematic data was recorded at 60Hz with four digital video camera. Two successful motions and failure motions for each subject were selected for three dimensional analysis. 1. Success Trail It was appear that success trail was larger than failure group in projection velocity, but success trail was smaller than failure trail in projection angle. Also it was appear that success trail was longer than failure group in the time required. Hand segment velocity and maximum velocity in success trail were larger than those in failure trail, and this result was increasing the projection velocity and finally increasing the vertical height of center of mass. At the take-off(event 2), flection amount of hip and knee joint angle was contributed to the optimal condition for the take-off and at the peak point, hip and knee joint angle was maximum flexed for reducing the moment of inertia. Also in this point, upper extremities of success trail extended more than those of failure trail. in this base, success trail in upward phase(p3) 2. Failure Trail It was appear that failure trail was smaller than success trail in projection velocity, but failure trail was larger than success trail in projection angle. Also it was appear that failure trail was more short than success trail in the time required. Hand segment velocity and maximum velocity in failure trail were smaller than those in success trail, and this result was reducing the projection velocity and finally reducing the vertical high of center of mass. At the take-off(event 2), flection amount of hip and knee joint angle wasn't contributed to the optimal condition for the take-off and at the peak point, hip and knee joint angle wasn't maximum flexed for reducing the moment of inertia. Also in this point, upper extremities of failure trail didn't extended more than those of success trail.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.95.1-95.1
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• 2012

Halo coronal mass ejections (HCMEs) are major cause of geomagnetic storms and their three dimensional structures are important for space weather. In this study, we compare three cone models: an elliptical cone model, an ice-cream cone model, and an asymmetric cone model. These models allow us to determine the three dimensional parameters of HCMEs such as radial speed, angular width, and the angle (${\gamma}$) between sky plane and cone axis. We compare these parameters obtained from three models using 62 well-observed HCMEs from 2001 to 2002. Then we obtain the root mean square error (RMS error) between maximum measured projection speeds and their calculated projection speeds from the cone models. As a result, we find that the radial speeds obtained from the models are well correlated with one another (R > 0.84). The correlation coefficients between angular widths are less than 0.53 and those between ${\gamma}$ values are less than 0.47, which are much smaller than expected. The reason may be due to different assumptions and methods. The RMS errors of the elliptical cone model, the ice-cream cone model, and the asymmetric cone model are 213 km/s, 254 km/s, and 267 km/s, respectively. Finally, we discuss their strengths and weaknesses in terms of space weather application.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.1
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• pp.81-87
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• 2012

This paper focuses on three-dimensional measurement system of micro balls on micro Ball-Grid-Array(BGA) packages in-line. Most of visual inspection system still suffers from sophisticate reflection characteristics of micro balls. For accurate shape measurement of them, a specially designed visual sensor system is proposed under the sensing principle of phase shifting moire interferometry. The system consists of a pattern projection system with four projection subsystems and an imaging system. In the projection system, four subsystems have spatially different projection directions to make target objects experience the pattern illuminations with different incident directions. For the phase shifting, each grating pattern of subsystem is regularly moved by PZT actuator. To remove specular noise and shadow area of BGA balls efficiently, a compact multiple-pattern projection and imaging system is implemented and tested. Especially, a sensor fusion algorithm to integrate four information sets, acquired from multiple projections, into one is proposed with the basis of Bayesian sensor fusion theory. To see how the proposed system works, a series of experiments is performed and the results are analyzed in detail.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.52.1-52.1
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• 2012

It is often said that there is little geometrical mind in Korean history. However, a method to project the surface of a sphere onto 2-dimensional plain was applied to the representative Korean star chart or Cheonsang Yeolcha Bunyajido (天象列次分野之圖). The method, called the equi-distant polar projection, was explained in detail in ancient Chinese history book of the Tang dynasty, which was originated from older history. Another method of the Mercator projection was introduced by the famous engineer Su Song (蘇頌) of the Song dynasty. The description has quite geometrical thoughts, especially the concept of infinity or convergence appears, However, this type of sky projection method was not widely used in east Asia. When the European Jesuits came to China to evangelize the Chinese people, they found that the Chinese people paid much attention to advanced European astronomical knowledge. Thus, they introduced the European astronomical knowledges into China, and the star chart was one of them. The projection method of the new charts were quite different from the Chinese tradition. When the Koreans brought those new star chart from China, they must have known the geometrical description of the method. The method was described in detail in a volume of Chongzhen Lishi (崇禎曆書) or Xiyang Xinfa Lishu (西洋新法曆書). The explanation consists of three part. One is the quantitative way; another is a geometrical way using axiomatic systems; and the other is the practical method to draw star chart with the geometical projection. However, when we see the Honcheon Jeondo (渾天全圖) that is thought to be duplicated by Kim Jeongho (金正浩), the new geometrical method was not so widely known to the Koreans. I will discuss the reason why the geometrical minds have not been widely adopted in the Korean civilization.

• Journal of Korean Society for Geospatial Information Science
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• v.20 no.1
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• pp.117-123
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• 2012

Many nations have been launched their own earth observation satellites due to much interest in space exploration. Because of this, the number of high resolution satellite are increasing day by day. With the development of web environment, general users have easy access to satellite images. The research conducted a basic study about web-based satellite photogrammetry in order to determine three dimensional coordinates easily without having profound knowledge of satellite sensor modeling. Various element technologies were analyzed to decide three dimensional coordinates by using high resolution satellite images in web environment, and case studies were conducted by using IKONOS satellite images. By applying parallel projection model, which is one of sensor modeling methods, epipolar image was created and prototype form of program that can decide three dimensional location in web environment was implemented. Through this, general users could decide three dimensional location easily in web environment and knew that already existed spatial information can be renewed and used in service area.

• Journal of Digital Contents Society
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• v.16 no.4
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• pp.605-613
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• 2015

This paper addresses the problem to make sparse the projection matrix in pattern recognition method. Recently, the size of computer program is often restricted in embedded systems. It is very often that developed programs include some constant data. For example, many pattern recognition programs use the projection matrix for dimension reduction. To improve the recognition performance, very high dimensional feature vectors are often extracted. In this case, the projection matrix can be very big. Recently, RSR(roated sparse regression) method[1] was proposed. This method has been proved one of the best algorithm that obtains the sparse matrix. We propose three methods to improve the RSR; outlier removal, sampling and elastic net RSR(E-RSR) in which the penalty term in RSR optimization function is replaced by that of the elastic net regression. The experimental results show that the proposed methods are very effective and improve the sparsity rate dramatically without sacrificing the recognition rate compared to the original RSR method.

• Journal of the Korea Computer Graphics Society
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• v.22 no.4
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• pp.1-9
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• 2016

In this paper we present a projection mapping system onto human's moving hand by a projector as information delivery media and Kinect to recognize hand motion. Most traditional projection mapping techniques project a variety of images onto stationary objects, however, our system provides new user experience by projecting images onto the center of the moving palm. We explain development process of the system, and production of content as applications on our system. We propose hardware organization and development process of open software architecture based on object oriented programming approach. For stable image projection, we describe a device calibration method between the projector and Kinect in three dimensional space, and a denoising technique to minimize artifacts from Kinect coordinates vibration and unstable hand tremor.

• Korean Journal of Optics and Photonics
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• v.9 no.6
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• pp.368-372
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• 1998

A 16-views 3 dimensional imaging system is designed by spatially combinding two 8-views time multiplexed image channels. Each 8-views channel composed of 3 primary color CRTs and a dichroic beam splitter which combining the three CRTs as one channel. Each CRT displays 8-view images time sequentially. These images are projected to a holographic screen of a size 1$\times$0.8 $m^2$ through a projection optics. Characteristics of the three different configurations of projection optics are examined with the optics designing program "DEMOS" to select an optimized projection optics for the system. The configulation of the optimized projection optics is found like following; images from each channel combined by two-fold mirror are projected by a projection objective through a 16-strips LCD shutter. In this configuration, the shutter should be located at the entrance pupil of the objective, and the folded edge of the two-fold mirror should contact symmetrically to the center line of the shutter.e shutter.