• Journal of Radiation Protection and Research
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• v.27 no.1
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• pp.67-75
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• 2002

The groundwater flow and contaminant transport numerical models have been established for understanding the movement of pollutants in surface soil environment. The numerical solutions were compared with the analytic solutions for the verification and the application of the models. The numerical solutions from the groundwater and transport models agreed welt with analytic solutions. Especially, the results of groundwater flow model were validated in one- and two-dimensional heterogeneous media. Therefore, it will represent well the characteristics of the heterogeneous media in the field applications. Also, the phenomena of the pollutant dispersion represented quite well by the advection and the hydrodynamic dispersion in the results of the transport model. The important input factor is the choice of complicated boundary conditions in operating the numerical models. The numerical results are influenced by the choice of the proper boundary conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.7
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• pp.721-730
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• 2012

The present paper presents a numerical study on multiphase flows induced by wall adhesion. The continuum surface force (CSF) model with the wall adhesion boundary condition model is used for calculating the surface tension force; this model is implemented in an in-house solution code (PowerCFD). The present method (code) employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with a volume capturing method (CICSAM) in a volume of fluid (VOF) scheme for phase interface capturing. The effects of wall adhesion are then numerically simulated by using the present method for a shallow pool of water located at the bottom of a cylindrical tank with no external forces such as gravity. Two different cases are computed, one in which the water wets the wall and one in which the water does not wet the wall. It is found that the present method efficiently simulates the surface tension-dominant multiphase flows induced by wall adhesion.

• Spatial Information Research
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• v.13 no.1 s.32
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• pp.55-63
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• 2005

Direct Georeferencing(DG) Is based on the direct measurement of the projection centers and rotation angle of sensor through loading the GPS and INS in aircraft. The methods can offer us to acquire the exterior orientation parameters with only minimum GCPs, even the ground control process could be completely skipped. Hence, as long as securing Digital Elevation Model (DEM), it is feasible to generate digital orthophotos without performing the aerial triangulation with Ground Control Point (GCP) surveying. In this study, the DEM is automatically generated by using a image matching technique based on aerial photos and exterior orientation parameters. This is followed by producing an orthophoto from these results. Finally, accuracy analysis of the georeferencing technique for generating orthoimage indicates that RMS errors of 62cm and 76cm occurred at the X and the Y axis, respectively. This means that the results fulfill the demanding accuracy of the 1:5000 digital map. Hence, it is possible to conclude from this study that the direct georeferencing based orthoimage generation method is able to effectively digital map update.

• Spatial Information Research
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• v.16 no.3
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• pp.317-330
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• 2008

In this paper, the acquisition of digital imagery and the orthoimage generation were performed to set up working process. And another purpose of this thesis is to evaluate the accuracy of orthoimage by overlapping digital topographic map and digital cadastral map on it. The digital topographic map and digital cadastral map were superimposed on the orthoimage to check the accuracy as another approach of evaluation. The RMSE is ${\pm}0.364m$ in X direction and ${\pm}0.413m$ in Y direction with digital topographical maps(1/5,000). And the RMSE is ${\pm}1.283m$ in X direction and ${\pm}1.085m$ in Y direction with digital cadastral map. It is necessary for the application of a newly developed digital aerial camera to make an exact synchronization between GPS/IMU data and image data, use a technology for setting a standard image resolution and the number of ground control points.

• Journal of Korean Society for Geospatial Information Science
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• v.12 no.3 s.30
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• pp.91-97
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• 2004

As for the former analogue method of photogrammetry, We have obtained final digital drawing by creating the stereo model from overlapped images through orientation process using plotting instrument and processing restitution procedure. However, digital photogrammetry batch processes such using small computer system thus We make an attempt automatization of the procedures. And without the production of stereo model, We could obtain 3D digital data through analysis method. Therefore, an objective of this study was to implement a surveying system that could 3D surveying positions using the digital image to reduce limitations of control point surveying and photographing conditions more efficiently to produce digital drawing. By the result, photogrammetry can practice and make out digital drawing to a computer by digital camera of a comparative low-cost. Small scale area can become practical use to drawing production etc. for facilities management because area can make out digital drawing economically than general surveying.

• Journal of Korean Society for Geospatial Information Science
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• v.15 no.4
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• pp.31-39
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• 2007

As the availability of images from airborne digital camera with high resolution is expanded, a lot of concern are shown about the production of orthoimage and digital map. This study presents the method of updating digital map using orthoimage from airborne digital camera image. Images were georectified using GPS surveying data. For the generation of orthoimage, Lidar DEM was used. The absolute positional accuracy of orthoimage was evaluated using GPS surveying data. And that of the building layer of digital map was estimated using the existed digital map at the scale of 1:1,000. The absolute positional accuracy of orthoimage was as followed: RMSE in X and Y were ${\pm}0.076m$ and ${\pm}0.294m$. The RMSE of the building layer were ${\pm}0.250m$ and ${\pm}0.210m$ in X and Y directions, respectively. The RMSE of the digital map using orthoimage from Aerial Digital Camera image fell within allowable error range established by NGII. Consequently, updating digital map using orthoimage from Aerial Digital Camera image can be applied to various fields including the construction of the framework data and the GIS of local government.

• Journal of the Korean Association of Geographic Information Studies
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• v.21 no.1
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• pp.106-114
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• 2018

DEM(Digital Elevation Model) are now easily produced with advancing remote sensing technology. Depending on desired task, UAV can produce high resolution DEM. But high resolution comes with issues of data storage and processing time and cost. To check the effect of DEM resolution, this study compares six geomorphological parameters derived from different resolution DEM in a test area around Chuncheon, Korea. The comparison analysis was based on statistics of each derivatives of slope, curvature, flow direction, flow accumulation, flow length and basin. As a result, it was found that DEM remained unchanged and so did the flow accumulation area. However, slope, curvature, flow length and basin numbers were decreased with the normalization of increasing pixel size. DEM resolution should be carefully selected depending on the precision of application required.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.10 no.2
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• pp.25-30
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• 1992

Most algorithms in computer vision and digital photogrammetry assume that digital stereo pairs are registered in epipolar geometry. But, an aerial stereo pair is not likely to be in epiplar geometry since the attitude of the camera at the instant of exposure is different at every exposure station. In this paper, stereo digital imagery is obtained from aerial stereo pair by scanner. Then procesure to resample the digital imagery to epipolar geometry using exterior orientation elements after absolute orientation is described. As a result, a stereo imagery in epipolar geometry is produced from stereo digital imagery. Epipolar imagery in this paper is applied to the image matching method by digital image correlation technique. Then, a digital elevation model is produced from the result of image matching. The digital elevation model in this paper is compared to the other digital elevation model produced by analytical plotter. As a result, an economical method to generate digital elevation model is presented.

• Journal of Korean Society for Geospatial Information Science
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• v.22 no.3
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• pp.121-128
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• 2014

This study investigated the accuracy of DEM generated by heterogeneous stereo satellite images based on RPC. Heterogeneous sensor images with different spatial resolution are SPOT-5 panchromatic and IKONOS images. For the accuracy evaluation of the DEM, we compared the DEMs generated from two kinds of sensors and that produced using homogeneous SPOT-5 and IKONOS stereo images. As results of the evaluation, accuracy of 3D positioning by heterogeneous images was substantially similar to that of homogeneous stereo images for exact conjugate points. But, in terms of quality of the DEM, DEM generated by heterogeneous sensor showed a lower accuracy about twice in RMSE and about 3 times in LE90 than that of homogeneous sensors. As a result, DEM can be generated by using heterogenous satellite imagery. But if we use a stereo image with different spatial resolution, the performance of image matching was very important factor for the production of high-quality DEM.

• Ecology and Resilient Infrastructure
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• v.6 no.4
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• pp.328-338
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• 2019

This paper presents the numerical simulations of future river bed changes using CCHE2D, a two-dimensional numerical model, for river confluences at the confluences of the Nakdong River and Gamcheon as well as Geum River and Mihocheon. The numerical simulations of future river bed changes were conducted for three years using hydrological data from August 30, 2012, to August 29, 2015 after the Four Major River Restoration Project. The simulation results demonstrated that river bed changes occurred actively near the confluence where sediment deposition was concentrated, resulting in the possibility of point bar formation. Through the numerical simulations, the characteristics of future river bed change was evaluated by investigating the characteristics of bed changes, average bed elevation changes, and the difference between deposition and erosion in the target section. The two-dimensional numerical model is expected to be used in the future to prepare effective stabilization plans for the tributary confluence.