• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.6
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• pp.499-506
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• 2019

NDSM (Normalized Digital Surface Model) is key information for the detailed analysis of remote sensing data. Although NDSM can be simply obtained by subtracting a DTM (Digital Terrain Model) from a DSM (Digital Surface Model), in case of UAV (Unmanned Aerial Vehicle) data, it is difficult to get an accurate DTM due to high resolution characteristics of UAV data containing a large number of complex objects on the ground such as vegetation and urban structures. In this study, RGB-based UAV vegetation index, ExG (Excess Green) was used to extract initial seed points having low ExG values for region growing such that a DTM can be generated cost-effectively based on high resolution UAV data. For this process, local window analysis was applied to resolve the problem of erroneous seed point extraction from local low ExG points. Using the DSM values of seed points, region growing was applied to merge neighboring terrain pixels. Slope criteria were adopted for the region growing process and the seed points were determined as terrain points in case the size of segments is larger than 0.25 ㎡. Various slope criteria were tested to derive the optimized value for UAV data-based NDSM generation. Finally, the extracted terrain points were evaluated and interpolation was performed using the terrain points to generate an NDSM. The proposed method was applied to agricultural area in order to extract the above ground heights of crops and check feasibility of agricultural monitoring.

• Journal of the Korean Association of Geographic Information Studies
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• v.19 no.4
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• pp.169-185
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• 2016

Recently mean stand height has been added as new attribute to forest type maps, but it is often too costly and time consuming to manually measure 9,100,000 points from countrywide stereo aerial photos. In addition, tree heights are frequently measured around tombs and forest edges, which are poor representations of the interior tree stand. This work proposes an estimation of mean stand height using an image-based point cloud, which was extracted from stereo aerial photo with FUSION S/W. Then, a digital terrain model was created by filtering the DSM point cloud and subtracting the DTM from DSM, resulting in nDSM, which represents object heights (buildings, trees, etc.). The RMSE was calculated to compare differences in tree heights between those observed and extracted from the nDSM. The resulting RMSE of average total plot height was 0.96 m. Individual tree heights of the whole study site area were extracted using the USDA Forest Service's FUSION S/W. Finally, mean stand height was produced by averaging individual tree heights in a stand polygon of the forest type map. In order to automate the mean stand height extraction using photogrammetric methods, a module was developed as an ArcGIS add-in toolbox.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2008.06a
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• pp.318-321
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• 2008

본 연구에서는 대용량의 항공 레이저 스캔 포인트 자료로부터 정규 격자 형태의 수치 표면 모델을 고속으로 생성하기 위하여 가상격자와 병렬처리를 기반으로 한 자료 처리 기법을 제안하였다. 수십$\sim$수백 평방 킬로미터 영역에 대하여 항공 레이저 스캔을 중복적으로 수행할 경우 포인트 수는 수억$\sim$수십억에 이르며 이를 일반적인 시스템에서 처리하는 데에는 한계가 존재한다. 이에 본 연구에서는 병렬처리를 위해 구성한 피씨 클러스터 상에서 자료를 분산시켜 가상격자를 이용하여 처리하는 방식을 제안하였다. 즉, 마스터 노드는 포인트 자료를 읽어 들여 포인트의 평면 좌표 값에 따라 슬래이브 노드로 전송하고 각 슬래이브 노드에서는 전송받은 포인트를 가상 격자에 저장한 후 보간(interpolation)을 수행한다. 보간 방식으로는 IDW(Inverse Distance Weightin)을 사용하였으며 제안한 방식의 효율성을 평가하기 위하여 사용된 슬래이브 노드 수에 대한 처리 시간을 측정하였다.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.4
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• pp.11-20
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• 2010

In situation that carbon dioxide emissions are being increased as urbanization, urban green space is being promoted as an alternative to find solution for these problems. In urban areas, trees have the ability to reduce carbon dioxide as well as to be aesthetic effect. In this study, we proposed the methodology which uses only LIDAR data in order to extract these trees information effectively. To improve the operational efficiency according to the extraction of trees, the proposed methodology was carried out using multiple data processing such as point, polygon and raster. Because the existing NDSM(Normalized Digital Surface Model) contains both the building and tree information, it has the problems of high complexity of data processing for extracting trees. Therefore, in order to improve these problems, this study used modified NDSM which was removed estimate regions of building. To evaluate the performance of the proposed methodology, three different zones which coexist buildings and trees within urban areas were selected and the accuracy of extracted trees was compared with the image taken by digital camera.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.213-216
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• 2004

본 연구에서는 복잡한 형상을 가진 음원으로부터 방사하는 음장을 등가음원법 (equivalent source method)을 이용하여 재구성한다. 일반적인 등가음원법의 기본 원리는 진동하는 물체의 표면 또는 내부에 등가음원을 분포시켜서 등가음원의 강도를 계산하는 방법이다. 각 등가음원의 강도는 음원의 경계 조건이나 측정된 음장 음압을 통해서 구할 수가 있으며 사용된 등가음원의 차수, 개수 그리고 위치 등은 고려되어야 할 중요한 변수들이다. 기존의 HELS (Helmholtz equation least square) 방법은 한 곳의 위치에 다양한 차수로 이루어진 등가음원을 사용하여 각 차수의 계수를 구하는 방법으로써 구형에 가까운 음원에 대해서 좋은 결과를 보이나 음장의 결과가 최대 차수의 선택에 따라서 큰 오차를 유발하는 문제점이 있다. 따라서 정규화 기법을 사용하여 음장을 재구성하기 위해 필요한 등가음원의 최적 차수를 구하고, 음원 내부에 최적 차수로 이루어진 등가음원을 여러 개의 점에 위치시켜서 재구성 정확도를 향상시켰다. 정규화된 등가음원법의 타당성 검증을 위하여 표면 일부가 진동하는 구에 대한 수치 해석 및 청소기 모델에 대한 음장 재구성 실험 을 수행하였다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.6
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• pp.405-416
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• 2019

Due to the development of information and communication technology, the production and processing speed of data is getting faster. To classify objects using machine learning, which is a field of artificial intelligence, data required for training can be easily collected due to the development of internet and geospatial information technology. In the field of geospatial information, machine learning is also being applied to classify or recognize objects using images and point clouds. In this study, the problem of manually constructing training data using existing digital map version 1.0 was improved, and the technique of classifying roads, buildings and vegetation using image and point clouds were proposed. Through experiments, it was possible to classify roads, buildings, and vegetation that could clearly distinguish colors when using true ortho-image with only RGB (Red, Green, Blue) bands. However, if the colors of the objects to be classified are similar, it was possible to identify the limitations of poor classification of the objects. To improve the limitations, random forest and support vector machine techniques were applied after band fusion of true ortho-image and normalized digital surface model, and roads, buildings, and vegetation were classified with more than 85% accuracy.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.103-108
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• 2018

The fragility curves for CFRD dams are derived in this study for probabilistic damage estimation as a function of a ground motion intensity. The dam crest settlement, which is a widely used damage index, is used for minor, moderate, and extensive damage states. The settlement is calculated from nonlinear dynamic numerical simulations. The accuracy of the numerical model is validated through comparison with a centrifuge test. The fragility curve is represented as a log normal distribution function and presented as a function of the peak ground acceleration. The fragility curves developed in this study can be utilized for real time assessment of the damage of dams.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2
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• pp.13-22
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• 1994

A theoretical model is studied to describe the sound radiation by the surface vibration of in-service tires. The tire is modeled as a circular ring model. The effects of normalized frequency and structrual loss factor are included. Through numerical integration of the sound pressure, the radiated sound power is calculated as a fuction of normalized frequency and structural loss factor. The basic sound radiation mechanism is shown to be the damped progressive wave field on the structure in the vicinity of the applied force. The results indicate that the potential sound reduction might be obtained if values of normalized frequency and structural loss factor are investigated.