• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.2
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• pp.265-271
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• 2010

This paper discusses a new software package, DEM_Comp, developed for effectively compressing large digital elevation model (DEM) data sets based on Lempel-Ziv-Welch (LZW) compression and Huffman coding. DEM_Comp was developed using the $C^{++}$ language running on a Windows-series operating system. DEM_Comp was also tested on various test sites with different territorial attributes, and the results were evaluated. Recently, a high-resolution version of the DEM has been obtained using new equipment and the related technologies of LiDAR (LIght Detection And Radar) and SAR (Synthetic Aperture Radar). DEM compression is useful because it helps reduce the disk space or transmission bandwidth. Generally, data compression is divided into two processes: i) analyzing the relationships in the data and ii) deciding on the compression and storage methods. DEM_Comp was developed using a three-step compression algorithm applying a DEM with a regular grid, Lempel-Ziv compression, and Huffman coding. When pre-processing alone was used on high- and low-relief terrain, the efficiency was approximately 83%, but after completing all three steps of the algorithm, this increased to 97%. Compared with general commercial compression software, these results show approximately 14% better performance. DEM_Comp as developed in this research features a more efficient way of distributing, storing, and managing large high-resolution DEMs.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2002.04a
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• pp.129-139
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• 2002

DEM을 구축하는 여러 방법 중 항공레이저측량을 이용하여 DEM을 구축하면 정확도 및 품질이 우수하고, 현시성 있는 DEM을 얻을 수 있다. 이에, 본 연구에서는 기존의 DEM구축방법과 신기술에 의한 DEM 구축방법을 품질 및 경제적 면에서 비교ㆍ평가하여 우리나라 국가 DEM의 구축방안을 제안하는데 그 목적이 있으며, 이를 위하여 DEM의 소요정확도 파악, 지형(또는 사용목적)별 적정한 격자간격 도출, DEM 구축방법별 경제성을 분석하고 추진일정을 제안하였다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.33 no.5
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• pp.443-451
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• 2015

In photogrammetry, GCPs (Ground Control Points) have traditionally been used to determine EOPs (Exterior Orientation Parameters) and to produce DEM (Digital Elevation Model). The existing DEM can be used as GCPs, where the observer’s approach is a difficult area, because it is very restrictive to survey in the field. For this, DEM matching should be performed. This study proposed the fusion method using ICP (Iterative Closest Point) and RT (proposed method by Rosenholm and Torlegard, 1988) in order to improve accuracy of the DEM matching. The proposed method was compared to the ICP method to evaluate its usefulness. Pseudo reference DEM with resolution 10m, and modified DEM (random-numbers are added from 0 to 2 at height; scale is 0.9; translation is 100 meters in 3-D axes; rotation is from 10° to 50° from the reference DEM) were used in the experiment. The results proposed accuracy was highest in the matching and absolute orientation. In the case of ICP, according to rotation of the modified DEM being increased, absolute orientation error is increased, while the proposed method generally showed consistent results without increasing the error. The proposed method would be applied to matching when the DEM is modified up to 30° rotation, compared to the reference DEM, based on the results of experiments. In addition when we use Drone, this method can be utilized to identify EOPs or detect 3-D surface deformation from the existing DEM of the inaccessible area.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.5
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• pp.443-451
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• 2006

DEM has been used for various purposes overall fields of engineering, the fields of civil engineering, military, communication, environment, and so forth and its applications are being extending increasingly. It is well hewn that LiDAR DEM is definitely superior to the other surveying methods. But LiDAR DEM run short of a full study about vertical accuracy. In order to assess LiDAR DEM, total 35 stations were selected and surveyed by GPS for utilizing as reference data. And then accuracy of LiDAR DEM was analyzed by comparison between both LiDAR DEM and CPS surveying. The RMSE of ${\pm}0.109m$ was shown in vertical direction. It is within the permissible accuracy required for mapping on a scale of 1 to 500 and 1 to 1000 on the mapping rule notified by the National Geographic Information Institute. It is expected that the results of this study will be fully used in the field of large scale DEM generation and be utilized as basic information in applied field of LiDAR DEM.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.20 no.3
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• pp.303-311
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• 2002

Recently, the research that analyze topography parameters that need in hydrology analysis using GIS techniques is achieved. DEM that is used in topography analysis can be constructed effectively using contour data of digital map. Therefore, DEM's applicability is increasing gradually in several fields. In this study, DEM of 20∼l00m grid size was applied PYONGCHANG river and JUBANG river basin to analyze what effect DEM grid size causes about slope and drainage watershed at topography parameter extraction. This study drew a regression equation about slope change by DEM grid size. As a result, according as DEM grid size increases, slope decreases, and basin area could know that is not change almost.

• Korean Journal of Remote Sensing
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• v.18 no.4
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• pp.221-231
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• 2002

In this study we applied a DEM generation algorithm developed in-house to satellite images at various resolution and discussed the results. We tested SPOT images at l0m resolution, EOC images at 6.6m and IKONOS images at 1m resolution. These images include the same urban area in Daejeon city. For camera model, we used Gupta & Hartley's(1997) DLT model for all three image sets. We carried out accuracy assessment using USGS DTED for SPOT and EOC and 23 check points for IKONOS. The assessment showed that SPOT DEM had about 38m RMS error, EOC DEM 12m RMS error and IKONOS DEM 6.5m RMS error. In terms of image resolution, SPOT and EOC DEM error corresponds to 2∼4 pixels where as IKONOS DEM error 6∼7pixels. IKONOS DEM contains more errors in pixels. However, in IKONOS DEM, individual buildings, apartments and major roads are identifiable. All three DEMs contained errors due to height discontinuity, occlusion and shadow. These experiments show that our algorithm can generate urban DEM from 1m resolution and that, however, we need to improve the algorithm to minimize effects of occlusion and building shadows on DEMs.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2002.04a
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• pp.187-194
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• 2002

본 논문에서는 SPOT 입체영상을 이용하여 광범위한 지역의 DEM을 제작할 경우 DEM 모자이크 과정에서 발생할 수 있는 접합선(seam-line)을 최소화할 수 있는 방법을 연구하였다. 지상의 60km$\times$60km 영역을 촬영할 수 있는 SPOT 위성의 입체 영상으로부터 구성한 단일 모델은 일반적으로 관심 있는 지역의 DEM을 제작하기에 충분히 넓은 지역을 포함할 수 있다. 그러나 광범위한 지역의 DEM 제작을 위해서는, 각각의 입체영상을 통해 제작된 DEM들을 접합해야 하며, 이 때 발생되는 접합선을 효과적으로 제거하는 작업이 필요하다. 이를 위해 SPOT 위성영상의 블록 조정 방법을 이용하여 종횡접합모델을 구성하고 중복되는 인접한 SPOT DEM간의 표고값을 일치시키므로써 DEM 접합선의 발생을 최소화하여 모자이크시 작업량을 줄이고자 한다. 본 논문에서는 기존의 지상기준점과 추가로 관측한 영상접합점을 이용하여 종횡접합 블록을 구성하고 광속조정 방법을 적용하여 블록에 포함된 위성영상의 외부표정요소를 계산하였다. 블록모델을 이용하여 DEM을 제작할 경우 접합선 탐색 및 blending 작업 없이 단순중첩 방법으로도 DEM 모자이크 작업을 빠르게 수행할 수 있음을 확인하였다.

• Tunnel and Underground Space
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• v.13 no.3
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• pp.207-214
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• 2003

To obtain Digital Elevation Model(DEM) from an exposed rock mass, techniques such as laser scanning and digital stereo photogrammetric technique are recently applied. We have obtained the DEM of the rock slope using above techniques in this study, and examined a suitability and improvement of the photogrammetry for the rock slope by overlapping the DEM. This study can be applied to the measurement of fracture orientations, the prediction of rock joint network, and the analysis on the change of the rock slope.

• Journal of the Korean Association of Geographic Information Studies
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• v.1 no.1
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• pp.3-7
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• 1998

The issue of data accuracy brings a different perspective to the issue of GIS modeling, calls into a question the usefulness of data models such as DEM. Accuracy can be determined by randomly checking positional and attribute accuracy within a GIS data layer. With the increasing availability of DEM and the software capable of processing them, it is worthwhile to call attention for data accuracy and error analysis as GIS application depends on the priori established spatial data. The purpose of this paper was to investigate methods for data accuracy measurement and error detection methodology with two types of DEM's: 1 to 24,000 and 1 to 250,000 DEM released by U.S. Geological Survey. Another emphasis was given to the development of methodology for processing DEM's to create Arc/Info and GRASS layers. Data accuracy analysis with DEM was applied to a 250 sq.km area and an error was detected at a scale of 1:24,000 DEM. There were two possible reasons for this error: gross errors and blunders.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.4
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• pp.359-365
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• 2008

This paper focused on generation of more accurate DEM and analysis of accuracy. For this, we applied suitable sensor modeling technique for each satellite image and automatic pyramid matching using image pyramid was applied. Matching algorithm based on epipolarity and scene geometry also was applied for stereo matching. IKONOS, Quickbird, SPOT-5, Kompsat-2 were used for experiments. In particular, we applied orbit-attitude sensor modeling technique for Kompsat-2 and performed DEM generation successfully. All DEM generated show good quality. Assessment was carried out using USGS DTED and we also compared between DEM generated in this research and DEM generated from common software. All DEM had $9m{\sim}12m$ Mean Absolute Error and $13m{\sim}16m$ RMS Error. Experimental results show that the DEMs of good performance which is similar to or better than result of DEMs generated from common software.