• Korean Journal of Remote Sensing
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• v.29 no.2
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• pp.183-195
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• 2013

Real-time high-precision image georeferencing is important for the realization of image based precise navigation or sophisticated augmented reality. In general, high-precision image georeferencing can be achieved using the conventional simultaneous bundle adjustment algorithm, which can be performed only as post-processing due to its processing time. The recently proposed sequential bundle adjustment algorithm can rapidly produce the results of the similar accuracy and thus opens a possibility of real-time processing. However, since the processing time still increases linearly according to the number of images, if the number of images are too large, its real-time processing is not guaranteed. Based on this algorithm, we propose a modified fast algorithm, the processing time of which is maintained within a limit regardless of the number of images. Since the proposed algorithm considers only the existing images of high correlation with the newly acquired image, it can not only maintain the processing time but also produce accurate results. We applied the proposed algorithm to the images acquired with 1Hz. It is found that the processing time is about 0.02 seconds at the acquisition time of each image in average and the accuracy is about ${\pm}5$ cm on the ground point coordinates in comparison with the results of the conventional simultaneous bundle adjustment algorithm. If this algorithm is converged with a fast image matching algorithm of high reliability, it enables high precision real-time georeferencing of the moving images acquired from a smartphone or UAV by complementing the performance of position and attitude sensors mounted together.

• Journal of Ocean Engineering and Technology
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• v.31 no.1
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• pp.69-79
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• 2017

This paper presents the operations of a multi-beam echo sounder (MBES) installed on the deep-sea remotely operated vehicle (ROV) Hemire. Hemire explored hydrothermal vents in the Forecast volcano located near the Mariana Trench in March of in 2006. During these explorations, we acquired profiling points on the routes of the vehicle using the MBES. Information on the position, depth, and attitude of the ROV are essential to obtain higher accuracy for the profiling quality. However, the MBES installed on Hemire does not have its own position and depth sensors. Although it has attitude sensors for roll, pitch, and heading, the specifications of these sensors were not clear. Therefore, we had to merge the high-performance sensor data for the motion and position obtained from Hemire into the profiling data of the MBES. Then, we could properly convert the profiling points with respect to the Earth-fixed coordinates. This paper describes the integration of the MBES with Hemire, as well as the coordinate conversion between them. Bathymetric maps near the summit of the Forecast volcano were successfully collected through these processes. A comparison between the bathymetric maps from the MBES and those from the Onnuri Research Vessel, the mother ship of the ROV Hemire for these explorations, is also presented.

• Smart Structures and Systems
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• v.24 no.6
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• pp.769-781
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• 2019

Dynamic displacement response of civil structures is an important index for in-construction and in-service structural condition assessment. However, accurately measuring the displacement of large-scale civil structures such as high-rise buildings still remains as a challenging task. In order to cope with this problem, a vision-based system with the use of industrial digital camera and image processing has been developed for long-distance, remote, and real-time monitoring of dynamic displacement of supertall structures. Instead of acquiring image signals, the proposed system traces only the coordinates of the target points, therefore enabling real-time monitoring and display of displacement responses in a relatively high sampling rate. This study addresses the in-situ experimental verification of the developed vision-based system on the Canton Tower of 600 m high. To facilitate the verification, a GPS system is used to calibrate/verify the structural displacement responses measured by the vision-based system. Meanwhile, an accelerometer deployed in the vicinity of the target point also provides frequency-domain information for comparison. Special attention has been given on understanding the influence of the surrounding light on the monitoring results. For this purpose, the experimental tests are conducted in daytime and nighttime through placing the vision-based system outside the tower (in a brilliant environment) and inside the tower (in a dark environment), respectively. The results indicate that the displacement response time histories monitored by the vision-based system not only match well with those acquired by the GPS receiver, but also have higher fidelity and are less noise-corrupted. In addition, the low-order modal frequencies of the building identified with use of the data obtained from the vision-based system are all in good agreement with those obtained from the accelerometer, the GPS receiver and an elaborate finite element model. Especially, the vision-based system placed at the bottom of the enclosed elevator shaft offers better monitoring data compared with the system placed outside the tower. Based on a wavelet filtering technique, the displacement response time histories obtained by the vision-based system are easily decomposed into two parts: a quasi-static ingredient primarily resulting from temperature variation and a dynamic component mainly caused by fluctuating wind load.

• Journal of the Korean Geographical Society
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• v.51 no.4
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• pp.491-508
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• 2016

This study has taken the Myeongjidong island, which has experienced spatial change due to various reasons ranging from the Japanese colonial era until today, as an instance in order to comprehend macroscopic spatial change of the Nakdonggang Delta and the adaptation process of the locals in a microscopic point of view. Spatial change of the Myeongjidong has been confirmed by collecting maps such as the atlas of late period of Chosun published in 1910, topographic map, regional geography, city records, and by applying coordinates with geographic reference function of GIS program, then checking for time sequential space change of individual regions. Space change driven by the Japanese government-general of Korea, Gimhae Irrigation Association, and by national policy or planning brought about environmental and humanistic changes unlike ever before, and land usage, housing and industry of the region and the locals experienced various adaptation processes. Such processes were compiled through collection and comparison of literature, and supplementation from interview of the locals during field study. As for the research region, it ranged from the construction of Nakdonggang bank and Myeongji seawall of 1935, agricultural rural landscape formed after the area expansion project by Gimhae Irrigation Association in 1940, to landscape that are becoming mercantile and urban due to the developmental plans of national and local governments.

• Journal of the Korean association of regional geographers
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• v.23 no.2
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• pp.376-387
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• 2017

This paper attempts to analyze the geographical characters of Twitter data and presents analysis potentials for social network analysis in geography. First, this paper suggests a methodology for a topic modeling-based approach in order to identify the geographical characteristics of tweets, including an analysis flow of Twitter data sets, tweet data collection and conversion, textural pre-processing and structural analysis, topic discovery, and interpretation of tweets' topics. GPS coordinates referencing tweets(geotweets) were extracted among sampled Twitter data sets because it contains the tweet place where it was created. This paper identifies a correlated relationship between some specific topics and local places in Jeju. This correlation is closely associated with some place names and local sites in Jeju Island. We assume it is the intention of tweeters to record their tweet places and to share and retweet with other tweeters in some cases. A surface density map shows the hotspots of tweets, detecting around some specific places and sites such as Jeju airport, sightseeing sites, and local places in Jeju Island. The hotspots show similar patterns of the floating population of Jeju, especially the thirty-year age group. In addition, a topic modeling algorithm is applied for the geographical topic discovery and comparison of the spatial patterns of tweets. Finally, this empirical analysis presents that Twitter data, as social network data, provide geographical significance, with topic modeling approach being useful in analyzing the textural features reflecting the geographical characteristics in large data sets of tweets.

• Journal of Cadastre & Land InformatiX
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• v.49 no.1
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• pp.85-101
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• 2019

Recently, thank to the popularization of light-weight drone through the significant developments in computer technologies as well as the advanced automated procedures in photogrammetry, Unmanned Aircraft Systems have led to a growing interest in industry as a whole. Documentation, maintenance, and restoration projects of large scaled cultural property would required accurate 3D phenomenon modeling and efficient visual inspection methods. The object of this study verify on the accuracies achieved of 3D phenomenon reconstruction as well as on the validity of the preservation, maintenance and restoration of large scaled cultural property by UAS photogrammetry. The test object is cltural heritage(treasure 1324) that is the rock-carved standing Bodhisattva in Soraesan Mountain, Siheung, documented in Goryeo Period(918-1392). This standing Bodhisattva has of particular interests since it's size is largest stone Buddha carved in a rock wall and is wearing a lotus shaped crown that is decorated with arabesque patterns. The positioning accuracy of UAS photogrammetry were compared with non-target total station survey results on the check points after creating 3D phenomenal models in real world coordinates system from photos, and also the quantified informations documented by Culture Heritage Administration were compared with UAS on the bodhisattva image of thin lines. Especially, tests the validity of UAS photogrammetry as a alternative method of visual inspection methods. In particular, we examined the effectiveness of the two techniques as well as the relative fluctuation of rock surface for about 2 years through superposition analysis of 3D points cloud models produced by both UAS image analysis and ground laser scanning techniques. Comparison studies and experimental results prove the accuracy and efficient of UAS photogrammetry in 3D phenomenon modeling, maintenance and restoration for various large-sized Cultural Heritage.

• Journal of Convergence for Information Technology
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• v.11 no.1
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• pp.136-142
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• 2021

Open-pit mine development requires continuous management because of topographical changes and there is a risk of accidents if the current status survey is performed directly in the process of calculating the earthwork. In this study, the application of UAV photogrammetry, which can acquire spatial information without direct human access, was applied to open-pit mines development area and analyzed the accuracy, earthwork, and mountain restoration plan to determine its applicability. As a result of accuracy analysis at checkpoint using ortho image and Digital Surface Model(DSM) by UAV photogrammetry, Root Mean Square Error(RMSE) is 0.120 m in horizontal and 0.150 m in vertical coordinates. This satisfied the tolerance range of 1:1,000 digital map. As a result of the comparison of the earthwork, UAV photogrammetry yielded 11.7% more earthwork than the conventional survey method. It is because UAV photogrammetry shows more detailed topography. And result of monitoring mountain restoration showed possible to determine existence of rockfall prevention nets and vegetation. If the terrain changes are monitored by acquiring images periodically, the utility of UAV photogrammetry will be further useful to open-pit mine development.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.3
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• pp.222-232
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• 2014

Purpose: This study aims to investigate if 2D analysis method is applicable to analysis of CBCT by comparing measuring points of CBCT with those of Adjusted 2D Lateral Cephalogram (Adj-Ceph) with magnification adjusted to 100% and finding out at which landmarks the difference in position appear. Materials and methods: CBCT data and Adj-Ceph (100% magnification) data from 50 adult patients have been extracted as research objects, and the horizontal (Y axis) and vertical (Z axis) coordinates of landmarks were compared. Landmarks have been categorized into 4 groups by the position and whether they are bilaterally overlapped. Paired t-test was used to compare differences between Adj-Ceph and CBCT. Results: Significant difference was found at 11 landmarks including Group B (S, Ar, Ba, PNS), Group C (Po, Or, Hinge axis, Go) and Group D (U1RP, U6CP, L6CP) in the horizontal (Y) axis while all the landmarks in vertical (Z) axis showed significant difference (P<.05). As a result of landmark difference analysis, a meaningful difference with more than 1 mm at 13 landmarks were indentifed in the horizontal axis. In the vertical axis, significant difference over 1 mm was detected from every landmark except Sella. Conclusion: Using the conventional lateral cephalometric measurements on CBCT is insufficient. A new 3D analysis or a modified 2D analysis adjusted on 19 landmarks of the vertical axis and 13 of the horizontal axis are needed when implementing CBCT diagnosis.

• Journal of Korea Water Resources Association
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• v.55 no.2
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• pp.135-145
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• 2022

This study aims to verify the Drone utilization and the accuracy of the global navigation satellite system (GNSS), Drone RGB (Photogrammetry) (D-RGB), and Drone LiDAR (D-LiDAR) surveying performance in the downstream reaches of the local stream. The results of the measurement of Ground Control Point (GCP) and Check Point (CP) coordinates confirmed the excellence. This study was carried out by comparing GNSS, D-RGB, and D-LiDAR with the values which the hydraulic characteristics calculated using HEC-RAS model. The accuracy of three survey methods was compared in the area of the study which is the ownership station, to 6 GCP and 3 CP were installed. The comparison results showed that the D-LiDAR survey was excellent. The 100-year frequency design flood discharge was applied in the channel sections of the small stream. As a result of D-RGB surveying 2.30 m and D-LiDAR 1.80 m in the average bed elevation, and D-RGB surveying 4.73 m and D-LiDAR 4.25 m in the average flood condition. It is recommended that the performance of D-LiDAR surveying is efficient method and useful as the surveying technique of the geospatial information using the drone equipment in stream channel.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2593-2600
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• 2013

The main purpose of this study is to carry out the performance evaluation of Ultra-light Fixed Wing UAV(Unmanned Aerial Vehicle) photogrammetry which is being, currently, applied for various fields such as cultural assets, accident survey, military reconnaissance work, and disaster management at home and abroad. Firstly, RMSE estimation of Aerial Triangulation (AT) are within approximately 0.10 cm in position (X, Y). And through the comparison of parcel's boundary points coordinates by terrestrial surveying and by UAV photogrammetry, the analysis shows that RMSE are shifted approximately 0.174~0.205 m in X-direction, 0.294~0.298 m in Y-direction respectively. Lastly, parcel's area by orthophoto of UAV photogrammetry and by that of cadastre register has been shown the difference by 0.118 m2. The results presented in this study is just one case study of orthophoto accuracy assessment of Ultra-light fixed wing UAV photogrammetry, hereafter various researches such as AT, direct-georeferencing, flight planning, practical applications, etc. should be necessary continuously.