• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.3
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• pp.353-360
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• 2012

This paper describes a SLAM method which estimates landmark locations and robot pose simultaneously. The particle filter can deal with nonlinearity of robot motion as well as the non Gaussian property of robot motion uncertainty and sensor error. The state to be estimated includes the locations of landmarks in addition to the robot pose. In the experiment, four beacons which transmit ultrasonic signal are used as landmarks. The robot receives the ultrasonic signals from the beacons and detects the distance to them. The method uses rang scanning sensor to build geometric feature of the environment. Since robot location and heading are estimated by the particle filter, the scanned range data can be converted to the geometric map. The performance of the method is compared with that of the deadreckoning and trilateration.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.4
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• pp.438-444
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• 2004

The intelligent robots that will be needed in the near future are human-friendly robots that are able to coexist with humans and support humans effectively. To realize this, robots need to recognize their position and posture in known environment as well as unknown environment. Moreover, it is necessary for their localization to occur naturally. It is desirable for a robot to estimate of his position by solving uncertainty for mobile robot navigation, as one of the best important problems. In this paper, we describe a method for the localization of a mobile robot using image information of a moving object. This method combines the observed position from dead-reckoning sensors and the estimated position from the images captured by a fixed camera to localize a mobile robot. Using the a priori known path of a moving object in the world coordinates and a perspective camera model, we derive the geometric constraint equations which represent the relation between image frame coordinates for a moving object and the estimated robot's position. Since the equations are based or the estimated position, the measurement error may exist all the time. The proposed method utilizes the error between the observed and estimated image coordinates to localize the mobile robot. The Kalman filter scheme is applied for this method. its performance is verified by the computer simulation and the experiment.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.11
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• pp.98-105
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• 2010

In this paper, double ball-bar is used to estimate the geometric errors of a rotary table, which includes one-axial motion, two-radial motions and two-tilt motions, except the angular positioning error. To simplify the measurement procedures, three measurement steps have been designed and developed. At each measurement step, one end of the double ball-bar is fixed at the nose of spindle and the other end is located on the rotary table. And specific circular test path is planned to keep the distance between two balls as constant at ideal case. The relationship including the geometric errors of a rotary table and the measured distance between two balls which is distorted by the geometric errors is defined by using ball-bar equation. Each geometric error is modeled as $4^{th}$ order polynomial considering $C^1$-continuity. Finally the coefficients of polynomial are calculated by least-square method. Simulation is done to check the validation of the suggested method considering set-up errors and measurement noise. Suggested method is applied to estimate geometric errors of a rotary table of a 5-axis machine tool.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.5
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• pp.251-258
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• 2004

This paper proposes a method for estimating the illuminant chromaticity using the distributions of the camera responses obtained by a CCD camera in a real-world scene. Illuminant estimation using a highlight method is based on the geometric relation between a body and its surface reflection. In general, the pixels in a highlight region are affected by an illuminant geometric difference, camera quantization errors, and the non-uniformity of the CCD sensor. As such, this leads to inaccurate results if an illuminant is estimated using the pixels of a CCD camera without any preprocessing. Accordingly, to solve this problem the proposed method analyzes the distribution of the CCD camera responses and selects pixels using the Mahalanobis distance in highlight regions. The use of the Mahalanobis distance based on the camera responses enables the adaptive selection of valid pixels among the pixels distributed in the highlight regions. Lines are then determined based on the selected pixels with r-g chromaticity coordinates using a principal component analysis(PCA). Thereafter, the illuminant chromaticity is estimated based on the intersection points of the lines. Experimental results using the proposed method demonstrated a reduced estimation error compared with the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2C
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• pp.156-165
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• 2006

In this paper, a new intelligent moving target tracking and surveillance system basing on the pan/tilt-embedded stereo camera system is suggested and implemented. In the proposed system, once the face area of a target is detected from the input stereo image by using a YCbCr color model and phase-type correlation scheme and then, using this data as well as the geometric information of the tracking system, the distance and 3D information of the target are effectively extracted in real-time. Basing on these extracted data the pan/tilted-imbedded stereo camera system is adaptively controlled and as a result, the proposed system can track the target adaptively under the various circumstance of the target. From some experiments using 480 frames of the test input stereo image, it is analyzed that a standard variation between the measured and computed the estimated target's height and an error ratio between the measured and computed 3D coordinate values of the target is also kept to be very low value of 1.03 and 1.18$\%$ on average, respectively. From these good experimental results a possibility of implementing a new real-time intelligent stereo target tracking and surveillance system using the proposed scheme is finally suggested.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.5
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• pp.995-1002
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• 2022

Global Navigation Satellite System(GNSS) is a convenient system that acquires position and time information of a receiver if only satellite signals can be received anywhere in the world. However navigation signals include errors and a position error occurs according to the reception state of the signal. Also, a position error is affected by the geometric arrangement of the satellites. Therefore a receiver position performance varies by the number and status of visible satellites The condition of satellite signals is not good when the satellite rises or sets and the position change of receiver occurs when the signal is blocked by an obstacle such as a building in the urban area. In this paper, we proposed methods to improve the GNSS performance by using pseudorange correction method estimating the correction amount and the visible satellites selection method. By applying the proposed methods to an environment in which the number of visible satellites changes variously, the performance enhancement was verified.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.28.4-29
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• 2010

이 연구는 심우주 추적망(Deep Space Network) 측정 시스템의 구현을 위한 한국형 심우주 항법 예비 소프트웨어(Korean Deep Space Orbit Determination Program version 1; K-DSODP ver.1)의 개발을 목표로 한다. 연구의 주 내용은 심우주 항법을 위한 기초 기술 연구로 지구로부터 달까지 진행하는 탐사선의 궤적 추정에 대한 것이며, 연구의 시작에 앞서 사용될 관측 데이터를 얻기 위해 한국형 심우주 항법 관측데이터 생성 소프트웨어(Korean Deep Space Observation Data Generation Program version 1; K-DSODGP ver.1)를 개발하여 사용하였다. 임의의 잡음이 추가된 가상의 관측 데이터를 생성한 후, 이 관측 데이터를 실제 궤도로 상정하여 기하학적인 관측 모델을 수립하였고, 일정한 시간 간격동안 모은 임의의 관측 데이터를 가지고 궤도 결정을 수행하여 추정된 궤도를 전파하였다. 궤도 결정 알고리즘을 구성하기 위해 기본적인 좌표계, 탐사선에 미치는 지구의 중력에 대한 동역학 모델, 천체력과 탐사선의 동역학 모델로 구성된 관측 모델들을 유도하였으며, 탐사선의 위치와 속도를 추정하는 과정에서 가중치 최소 자승법을 적용하여 추정 궤도와 실제 궤도의 최소화를 유도하였다. 이러한 일련의 과정을 통해 요구한 시각의 탐사선의 위치와 속도를 결정하는 궤도결정 시스템을 구현하였고, 궤도 결정 시스템의 성능을 평가하기 위해 전파된 궤도와 실제 궤도의 차이를 분석하였다. 결과적으로 300초마다 관측데이터를 받을 경우, 2일 이상의 궤도결정 시간간격을 상정했을 때 평균 오차는 각각 약 0.26km RMS(range), 6.84km/s RMS(range-rate) 이내의 결과를 얻었고, 600초마다 관측데이터를 받을 경우, 평균 오차는 각각 약 0.30km RMS (range), 6.35km/s RMS(range-rate) 이내의 안정적인 결과를 얻었다. 이 연구의 결과를 통하여 추후 심화된 심우주 항법 소프트웨어 개발을 위한 기반이 마련될 것이다.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.9
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• pp.155-163
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• 2012

The geometrical and electrical errors of array sensors can severely degrade the performance of array sensor system. Various calibration techniques are developed to alleviate this problem. In this paper, two different calibration methods with respect to location, gain and phase of array sensors are presented. One method applies the first-order Taylor series expansion to approximate the true steering vector from the nominal values of array sensors. Then a set of equations is formed by using the null characteristics of the MUSIC spectrum to estimate errors of location, gain and phase of array sensors. Another method estimates these errors based on the data covariance matrix of pilot sources. From the simulations, it is demonstrated that two calibration algorithms calibrated an array system successfully. In addition to that, Fistas and Manikas's algorithm is more robust against noise than Ng and Lie's one when SNR is from 10dB to 50dB.

• Korean Journal of Agricultural and Forest Meteorology
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• v.20 no.4
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• pp.376-385
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• 2018

To estimate the hourly temperature distribution due to solar radiation during the day, on slope in complex terrain, an empirical formula was developed including the hourly deviation in the observed temperature following solar radiation deviation, at weather stations on the east-facing and west-facing slopes. The solar radiation effect was simulated using the empirical formula to estimate hourly temperature at 11 weather observation sites in mountainous agricultural areas, and the result was verified for the period from January 2015 to December 2017. When the estimated temperature was compared with the control, only considering temperature lapse rate, it was found that the tendency to underestimate the temperature from 9 am to 3 pm was reduced with the use of an empirical formula in the form of linear expression; consequently, the estimation error was reduced as well. However, for the time from 5 pm to 6 pm, the estimation error was smaller when a hyperbolic equation drawn from the deviation in solar radiation on the slope, which was calculated based on geometric conditions, was used instead of observed values. The reliability of estimating the daytime temperature at 3 pm was compared with existing estimation model proposed in other studies; the estimation error could be mitigated up to an ME (mean error) of $-0.28^{\circ}C$ and RMSE (root mean square error) of $1.29^{\circ}C$ compared to the estimation error in previous models (ME $-1.20^{\circ}C$, RMSE $2.01^{\circ}C$).

• The Journal of the Acoustical Society of Korea
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• v.36 no.6
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• pp.419-424
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• 2017

TDoA (Time Difference-of Arrival) or DoA (Direction-of-Arrival) can be used for source localization. However, the localizing performance is dependent on relative position between source and receivers, receivers' geometric structure, sound speed, and so on. In this paper we propose a source localization method with enhanced performance that combines multiple information. The proposed method uses the time TDoA, DoA and sound speed as variables. LM (Levenberg-Marquardt) method which is one of nonlinear optimizations is applied. The performances of the proposed method was evaluated by simulation. As result of simulation, the proposed method has the lower average localizing error performance than the previous method.