• 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.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.210-217
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• 2022

Passive source depth estimation has been studied for decades since the source depth can be used for target classification, target tracking, etc. The purpose of this paper is to solve the problem of ambiguity in the previous paper [S.-il. Cho et al. (in Korean), J. Acoust. Soc. Kr. 38, 120-127 (2019)] that source depth is estimated in two points. The patterns of phase shift of Channel Impulse Response(CIR) reflected in ocean surface and bottom is used for removing ambiguity of the source depth estimation, and after removing ambiguity, source depth is estimated at one point through the intersection of CIR. In order to extract CIR in case of unknown source signal and continuous signal or noise, Ray-based blind deconvolution is used. The proposed algorithm is demonstrated through numerical simulation in ocean waveguide.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.127.4-127
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• 2001

Inspection and shape measurement of three-dimensional objects are widely needed in industries for quality monitoring and control. A number of visual or optical technologies have been successfully applied to measure three dimensional surfaces. Especially, the shape measurement using an interferometric principle becomes a successful methodology. However, those conventional interferometric methods to measure surface profile have an inherent shortcoming, namely 2∏ ambiguity problem. The problem inevitably happens when the object to be measured has discontinuous shape due to the repetition of interferometric signal with phase period of 2∏. Therefore, in this paper, we choose as a shape measuring method, ...

• IEMEK Journal of Embedded Systems and Applications
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• v.8 no.2
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• pp.111-119
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• 2013

This paper proposes one method on photometric stereo calibration using the constraint on light source directions in which the light sources have the unknown tilt and slant angles but the slant angles are the same. First, the constraint is analyzed based on the equation of linear ambiguity which leads to the conclusion that another constraint should be added to solve the calibration completely. Later, the combination of constraint on light source directions and the constraint that there exists at least six surface patches having known albedos is exploited to resolve the linear ambiguity up to an accurate and close-form solution. The effective performance of the proposed method is demonstrated through experiment results.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.3
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• pp.215-220
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• 2020

This paper deal with estimating the direction of arrival (DOA) of GNSS signal using two antennae for spoofing detection. A technique for estimating the azimuth angle of a received signal by applying the interferometer method to the GPS carrier signal is proposed. The experiment assumes two antennas placed on the earth's surface and estimates the azimuth angle when only GPS signal are received without spoofing signal. The proposed method confirmed the availability through GPS satellite placement simulation and experiments using a dual antenna GPS receiver. In this case of using dual antenna, an azimuth angle ambiguity of the received signal occurs with respect to the baseline between two antennas. For this reason, the accurate azimuth angle estimation is limits, but it can be used for deception by cross-validating the ambiguity.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.1
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• pp.85-91
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• 2008

White light scanning interferometry has gotten a firm position in 3D surface profile measuring field. Recently, the LCD industry gave a chance for this technology to enter into real industry fields. It is known that white-light phase-shifting algorithm give a best resolution compare to other algorithms, but there are some problems to be resolved. One of them is 300nm jump in height profile, called bat-wing effect. The main reason of this problem is an ambiguity of phase-peak detection algorithm, and some solution has been proposed, but it didn't work perfectly. In this paper, I will show the cases when these effects are occurred, and these height discrepancies will be almost disappeared when broad-band illuminators are used.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.409-414
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• 2010

This paper describes the surface form measurement of a spherical smooth surface by using single shot off-axis Fizeau interferometry. The demodulated phase map is obtained and unwrapped to remove the $2\pi$ ambiguity. The unwrapped phase map is converted to height and the 3D surface height of the surface object is reconstructed. The results extracted from the single shot off-axis geometry are compared with the results extracted from four-frame phase shifting in-line interferometry, and the results are in excellent agreement.

• Multiscale and Multiphysics Mechanics
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• v.1 no.1
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• pp.15-33
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• 2016

In this paper, an asymptotic method is employed to formulate nano- or micro-beams based on strain gradient elasticity. Although a basic theory for the strain gradient elasticity has been well established in literature, a systematic approach is relatively rare because of its complexity and ambiguity of higher-order elasticity coefficients. In order to systematically identify the strain gradient effect, an asymptotic approach is adopted by introducing the small parameter which represents the beam geometric slenderness and/or the internal atomistic characteristic. The approach allows us to systematically split the two-dimensional strain gradient elasticity into the microscopic one-dimensional through-the-thickness analysis and the macroscopic one-dimensional beam analysis. The first-order beam problem turns out to be different from the classical elasticity in terms of the bending stiffness, which comes from the through-the-thickness strain gradient effect. This subsequently affects the second-order transverse shear stress in which the surface shear stress exists. It is demonstrated that a careful derivation of a first strain gradient elasticity embraces "Gurtin-Murdoch traction" as the surface effect of a one-dimensional Euler-Bernoulli-like beam model.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.1
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• pp.149-157
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• 2008

If we use the microwave of SAR, we can observe ocean in spite of severe weather or night time. The sea surface image of SAR has numerous information about atmospheric phenomena related to surface wind field. The extracted wind information from SAR can be used diversely. In order to extract sea wind speed from SAR image, a generated wind direction from SAR and sigma nought should be input into wind model. Therefore, wind speed can be obtained by input wind direction into CMOD5 Model. Azimuth angle using CMOD5 Model is generated by added $90^{\circ}$ to Look angle which is extracted from SAR data file. A gained wind direction spectrum from SAR image has $180^{\circ}$ ambiguity because of 2D-FFT. This ambiguity should decide to use the location of land, wind direction in field or the result of numerical model. Consequently, wind direction using 2D-FFT is $3^{\circ}{\sim}7^{\circ}$ differences with actual surveying data. Wind speed by CMOD5 model is similar to actual surveying data as below 2m/s.

• Journal of the Korean Institute of Landscape Architecture
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• v.18 no.3 s.39
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• pp.115-135
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• 1990

The purpose of this study was to suggest an improvement proposal for colors in urban environment with special regard to the surface color and their situations of apartment buildings in Seoul. For this goal, 167 cases of different color types of apartment buildings were surveyed. And, the survey was performed in the view of color by areas, by localtion, by builder, by paint year, by built year, by appearance of building, and by surface texture to prove the influencing factors on the surface colors. These collected data analyzed and compared with the existing studies to find out the changing trend of colors. The results are as follows : 1) The use of neutral gray($26.4{\%}$) and warm color(YR, Y, GY; 56.4%) were dominant and the usage trend of higher 'value'(87.4%) and lower 'saturation'(73.0%) was obvious. Especially, the use of PB and P was noticeable. 2) In comparing the existing studies, the changing trend in the surface color pattern was found. That is, neutral gray was used dominantly in 1970's, warm color(YR, Y)in the middle of 1980's. In the end of 1980's, warm color were also used dominantly same as before and GY, PB, P were used noticeably with some rising tendency of higher 'value' and lower 'saturation' was obvious. 3) The results of analysis by localtion shows that the different color groups might exist in Seoul city. Neutral gray and YR were dominant in zone I. Warm colors(YR, Y, GY)were prevailed in zone II, III, IV. In zone V, many colors were evenly used. In zone VI, middle values at warm color were dominant. Progressively, these color groups with further study could be considered in the color management in urban environment possibly. 4) Surface color of apartment buildings were different from their builders. 5) Concerned with the painted year, the use of higher 'value' and lower 'saturation' was increased gradually with the change of times. 6) the analysis by the built year revealed that the 'value' of surface colors on the old buildings was lower than that of the new ones. 7) The 'value' of colors on the surface with texture was higher than that of the surface without texture. 8) In the combination of two colors, the use of 'value' with difference at the same 'hue' was found harmonions in many cases, but the 'saturation' in usage was included in the ambiguity (Moon & Spencer's term). The ambiguity in color harmony should be improved in the near future.