• 대한공간정보학회지
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• 제24권2호
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• pp.79-87
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• 2016

As 3D geospatial information is demanded, terrestrial laser scanners which can obtain 3D model of objects have been applied in various fields such as Building Information Modeling (BIM), structural analysis, and disaster management. To acquire precise data, performance evaluation of a terrestrial laser scanner must be conducted. While existing 3D surveying equipment like a total station has a standard method for performance evaluation, a terrestrial laser scanner evaluation technique for users is not established. This paper categorizes and analyzes error sources which generally occur in terrestrial laser scanning. In addition to the prior researches about categorizing error sources of terrestrial Laser scanning, this paper evaluates the error sources by the actual field tests for the smooth in-situ applications.The error factors in terrestrial laser scanning are categorized into interior error caused by mechanical errors in a terrestrial laser scanner and exterior errors affected by scanning geometry and target property. Each error sources were evaluated by simulation and actual experiments. The 3D coordinates of observed target can be distortedby the biases in distance and rotation measurement in scanning system. In particular, the exterior factors caused significant geometric errors in observed point cloud. The noise points can be generated by steep incidence angle, mixed-pixel and crosstalk. In using terrestrial laser scanner, elaborate scanning plan and proper post processing are required to obtain valid and accurate 3D spatial information.

• 한국수산과학회지
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• 제51권4호
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• pp.435-443
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• 2018

The Antarctic krill Euphausia superba is important commercially and ecologically as a basic component of the Antarctic Ocean ecosystem. To manage this resource, it is important to determine the distribution and standing of krill in the water layer. Acoustic methods can capture information about the entire water layer quickly. Acoustic surveys were conducted from March 3 to March 14, 2017, using the commercial fishing boat Sejong (7,765 tons). Acoustic systems with a frequency of 38 kHz and a 200 kHz commercial echo sounder (ES70, Simrad, Norway) were used and the acquired data were processed using post processing software. The density and standing of Antarctic krill were determined using the two-frequency difference method, using the characteristics of two frequencies. To compare the frequency difference of krill, the method using the frequency difference according to the krill length, recommended by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and the values extracted according to the krill length at survey stations where only krill were collected during the study period, were compared. The frequency difference ranges were 3.96-5.91 dB and -3.0~13.8 dB, respectively.

• 정보처리학회논문지D
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• 제19D권4호
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• pp.271-280
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• 2012

현재 소셜 네트워크 서비스(Social Network Service: SNS)의 이용자 수가 늘어나면서 SNS에서 생성되는 콘텐츠 데이터의 양도 기하급수적으로 늘어나고 있다. 이러한 SNS는 개인의 근황, 관심사를 전달하기 위해 사용하고, 친목도모, 엔터테인먼트, 제품 마케팅, 최신 뉴스 공유, 1인 미디어 등 다양한 목적으로 활용하고 있다. SNS가 스마트폰에서 사용 가능해지면서 사용자들은 언제, 어디서나 실시간으로 사회의 주요쟁점이나 사회구성원들의 주 관심사와 같은 콘텐츠를 기존 미디어 매체보다 빠르게 생성하고 확산시킨다. 기존 웹 콘텐츠 색인 기법은 색인대상이 다양하고 정확성에 중점을 두어 색인하므로 실시간으로 대량 생성되는 SNS 콘텐츠를 색인하는 기법으로 한계가 있다. 이러한 문제를 해결하기 위하여 관계형 DBMS기반 실시간 색인 기법이 있으나 색인대상의 축소와 색인 절차의 복잡성이 높다는 단점이 있다. 따라서 본 논문에서는 실시간으로 생성된 SNS콘텐츠를 색인하기 위하여 NoSQL기반 SNS 콘텐츠 생성시간과 키워드를 각각 색인하는 TK-Indexing 기법을 제안하여 기존 색인 기법의 복잡성을 개선한다.

• 디지털융복합연구
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• 제13권9호
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• pp.489-495
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• 2015

BI-RADS의 구분에 따라 Algorithm의 변화로 영상의 질을 개선하는 기법을 이용하여 시각적 가시화의 차이를 일치도와 민감도로 평가하였다. 유방촬영을 시행한 172명을 대상으로 유방촬영의 판독소견과 자료 체계의 신뢰도를 평가하였다. Category 5단계(C0,C1,C2,C3,C4), 유방 실질 함유량 4단계(Fatty, Fibroglandular, Heterogeneous nodular, Diffuse dense), 병변 3종류(석회화, 결절, 종괴)로 분류하여 TE와 PV의 신뢰도를 평가하고, 민감도와 진단의 일치도, 정확도를 평가함으로 다방면의 융복합적 분석을 하였다. TE보다 PV가 병변의 신뢰도와 민감도와 정확도가 높았다. 유방 실질 함유량에 따른 평가에서 정확도는 PV가 높았다. TE에서는 Fatty는 모두에서, Fibroglandular는 종괴와 석회화가, Diffuse dense는 결절과 석회화가 구별이 용이하였다. PV에서는 Fatty는 모두에서, Fibroglandular는 결절, Heterogeneous nodular은 결절과 종괴, Diffuse dense는 결절과 석회화가 구별이 용이하였다. 민감도는 결절은 Fatty, Fibroglandular, Heterogeneous nodular에서 TE가 더 민감했고, 종괴에서는 Heterogeneous nodular, Diffuse dense에서 TE가 더 민감했으며, 석회화에서는 모두에서 TE가 더 민감하였다. 이에 Algorithm 기법을 적절히 변화시켜 활용한다면 진단과 판독에 정확성을 높일 것이라 사료된다.

• 컴퓨터교육학회논문지
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• 제18권2호
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• pp.47-57
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• 2015

본 연구는 플립러닝 학습 프로그램을 초등학교 5학년 학생에게 사회과 수업에서 적용했을 때 학습동기 및 학업성취도에 미치는 효과를 알아보기 위하여 실험집단 24명, 통제집단 25명을 대상으로 실험을 하였다. 연구도구는 플립러닝 학습 프로그램, 학습동기 검사지, 학업성취도 검사지를 사용하였다. 연구절차는 사전검사, 실험처치, 사후검사 순으로 이루어졌으며 자료처리는 독립표본 t-검증과 대응표본 t-검증을 사용하였다. 연구결과 플립러닝 학습이 사회과 학습동기에 긍정적인 영향을 주는데 학습동기 요소 중 특히 주의집중, 자신감 향상에 영향을 주었다. 또한 플립러닝 학습은 학업성취도 향상에 긍정적인 효과를 미치는 것으로 나타났는데 학업성취도 상위수준 학생보다는 하위수준 학생에게 영향을 주는 것으로 나타났다.

• 한국정보통신학회논문지
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• 제2권3호
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• pp.343-352
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• 1998

DGPS 이용으로 Standalone GPS의 정확도와 동일한 위성을 사용하는 2개 또는 그 이상의 사용자 수신기에서 생기는 공통오차제거가 가능하게 되었다. 정확한 기준점을 갖는 DGPS 시스템은 기준국과 사용자 수신기에서 발생하는 공통오차를 계산하여 사용자 수신기의 의사거리 보정을 한다. 정확한 기준점 측정은 특정한 측량기구 시스템을 이용하여 각 위성의 parameter를 측정하고 후 처리하여 얻게되므로 상당한 시간과 비용이 불가피하다. 본 연구에서는 측량기준점을 바탕으로 한 DGPS시스템과 Sub-optimal 기준점을 이용한 DGPS 시스템을 자체 구현하였다. 각각의 RTCM 보정 데이터를 이용하여 얻은 오차범위를 분석 평가하였다. 연구결과 이 시스템이 민간 및 군의 특정한 해양활동 사용시에 활용될 수 있음을 보였다.

• 한국군사과학기술학회지
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• 제21권2호
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• pp.166-172
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• 2018

To develop and evaluate the real-time SAR(Synthetic Aperture Radar) motion measurement system, true antenna phase center(APC) positions during SAT(Synthetic Aperture Time) are needed. In this paper, CDGPS(Carrier phase Differential Global Positioning System) post processing method is proposed to get the true APC position for spotlight SAR image formation. The CDGPS position is smoothed to remove high frequency noise which exists inherently in the carrier phase measurement. This paper shows smoothed CDGPS data is enough to provide the true APC for high-quality SAR image formation through motion measurement result, phase error estimation and IRF(Impulse Response Function) analysis.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.347-352
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• 2006

Narrowband interference can severely degrade the performance of GPS receivers. Detecting the presence of interference and then characterizing it can lead to its removal. Receivers can be reconfigured to focus on other signals or satellites that are less vulnerable to that interference at that moment. Using hardware reconfigurability of FPGA receivers and characterizing the effect of narrowband interference on the GNSS signal quality lead us to a new RFI mitigation technique in which the highest quality and less vulnerable signal can be chosen at each moment. In the previous work [1], the post processing capability of a software GPS receiver, has been used to detect and characterize the CW interference. This is achieved by passing the GPS signal and the interference through the correlator. Then, using the conventional definition of C/No as the squared mean of the correlator output divided by its variance, the actual C/No for each satellite is calculated. In this work, first the 'Exclusion zone' for each satellite signal has been defined and then by using some experiments the effects of different parameters like signal power, jamming power and the environmental noise power on the Exclusion zone have been analyzed. By monitoring the Doppler frequency of each satellite and using the actual C/No of each satellite using the traditional definition of C/No and actual data from a software GPS receiver, the decision to reconfigure the receiver to other signal can be made.

• 천문학회지
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• 제54권6호
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• pp.171-182
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• 2021

The lack of short baselines, referred to as the short-spacing problem (SSP), is a well-known limitation of the performance of radio interferometers, causing a reduction of the flux detected from source structure on large angular scales. The very large number of antennas operated in the Atacama Large Millimeter/sub-millimeter Array (ALMA) generates situations for which the impact of the SSP takes a complex form, not simply measurable by a single number, such as the maximal recoverable scale. In particular, extended antenna configurations, complemented by a small group of closeby antennas at the centre of the array, may result in a double-humped baseline distribution with a significant gap between the two groups. In such cases one should adopt as the effective maximal recoverable scale the one associated with the extended array and use only the central array to recover missing flux, as one would do with single dish or ACA (Atacama Compact Array) observations. The impact of the missing baselines can be very important and may easily be underestimated, or even overlooked. The present study uses ALMA archival data of the ²⁹SiO(8-7) line emission of the AGB star W Hydrae for a demonstration. A critical discussion of the reliability of the observations away from the star is presented together with comments of a broader scope. Properties of the circumstellar envelope of W Hya within ~15 au from the star, many of which are not mentioned in the published literature, are briefly described and compared with R Doradus, an AGB star having properties very similar to W Hya.

• 한국기계가공학회지
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• 제17권6호
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• pp.68-74
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• 2018

Study on the Ti-6Al-4V have been carried out using cutting simulation, and researches for cutting force and chip shape prediction have been actively conducted under various conditions. However, a 3D printer application method using Ti-6Al-4V metal powder material as a high-power method has been studied for the purpose of prototyping, mold modification and product modification while lowering material removal rate. However, in the case of products / parts made of 3D printers using powder materials, problems may occur in the contact surface during tolerance management and assembly due to the degradation of the surface quality. As a result, even if a 3D printer is applied, post-processing through cutting is essential for surface quality improvement and tolerance management. In the cutting simulation, the cutting force and the chip shape were predicted based on the Johnson-Cook composition equation, but the shape of the shear type chip was not predictable. To solve this problem, we added a damaging term or strain softening term to the Johnson-Cook constitutive equation to predict chip shape. In this thesis, we applied the constant value of the S-K equations to the cutting simulation to predict the cutting force and compare with the experimental data to verify the validity of the cutting simulation and analyzed the machining characterization by considering conditions.