• Journal of Auto-vehicle Safety Association
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• v.14 no.2
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• pp.39-44
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• 2022

This paper presents LiDAR static obstacle map based vehicle position correction algorithm for urban autonomous driving. Real Time Kinematic (RTK) GPS is commonly used in highway automated vehicle systems. For urban automated vehicle systems, RTK GPS have some trouble in shaded area. Therefore, this paper represents a method to estimate the position of the host vehicle using AVM camera, front camera, LiDAR and low-cost GPS based on Extended Kalman Filter (EKF). Static obstacle map (STOM) is constructed only with static object based on Bayesian rule. To run the algorithm, HD map and Static obstacle reference map (STORM) must be prepared in advance. STORM is constructed by accumulating and voxelizing the static obstacle map (STOM). The algorithm consists of three main process. The first process is to acquire sensor data from low-cost GPS, AVM camera, front camera, and LiDAR. Second, low-cost GPS data is used to define initial point. Third, AVM camera, front camera, LiDAR point cloud matching to HD map and STORM is conducted using Normal Distribution Transformation (NDT) method. Third, position of the host vehicle position is corrected based on the Extended Kalman Filter (EKF).The proposed algorithm is implemented in the Linux Robot Operating System (ROS) environment and showed better performance than only lane-detection algorithm. It is expected to be more robust and accurate than raw lidar point cloud matching algorithm in autonomous driving.

• Korean Journal of Remote Sensing
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• v.31 no.5
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• pp.461-471
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• 2015

In this study, we generated orthoimages and Digital Elevation Model (DEM) from Unmanned Aerial Vehicle (UAV) to confirm the accuracy of possibility of geospatial information system generation, then compared the DEM with the topographic height values measured from Real Time Kinematic-GPS (RTK-GPS). The DEMs were generated from aerial triangulation method using fixed-wing UAV and rotary-wing UAV, and DEM based on the waterline method also generated. For the accurate generation of mosaic images and DEM, the distorted images occurred by interior and exterior orientation were corrected using camera calibration. In addition, we set up the 30 Ground Control Points (GPCs) in order to correct of the UAVs position error. Therefore, the mosaic images and DEM were obtained with geometric error less than 30 cm. The height of generated DEMs by UAVs were compared with the levelled elevation by RTK-GPS. The value of R-square is closely 1. From this study, we could confirm that accurate DEM of the tidal flat can be generated using UAVs and these detailed spatial information about tidal flat will be widely used for tidal flat management.

• International Journal of Control, Automation, and Systems
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• v.6 no.4
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• pp.534-543
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• 2008

To use the Global Positioning System (GPS) carrier phase measurement for precise positioning, the integer ambiguities at the early stage of most algorithms must be determined. Furthermore, if a precise positioning is to be applied to real time navigation, fast determination and validation methods for integer ambiguity are essential. In this paper, the Wald test that simultaneously determines and validates integer ambiguities is used with assistance of the Inertial Navigation System (INS) to improve its performance. As the Wald test proceeds, it assigns a higher probability to the candidate that is considered to be true at each time step. The INS information is added during the Wald test process. Large performance improvements were achieved in convergence time as well as in requiring fewer observable GPS satellites. To test the performance improvement of the Wald test with the INS information, experimental tests were conducted using a ground vehicle. The vehicle moved in a prescribed trajectory and observed seven GPS satellites. To verify the effect of the INS information on the Wald test, the convergence times were compared with cases that considered the INS information and cases that did not consider the INS information. The results show that the benefits of using the INS were emphasized as fewer GPS satellites were observable. The performance improvement obtained by the proposed algorithm was shown through the fast convergence to the true hypothesis when using the INS measurements.

• International Journal of Aeronautical and Space Sciences
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• v.5 no.2
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• pp.1-8
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• 2004

Real-Time Kinematic GPS positioning is widely used for many applications.Resolving ambiguities is the key to precise positioning. Integer ambiguity resolution isthe process of resolving the unknown cycle ambiguities of double difference carrierphase data as integers. Two important issues of resolving are efficiency andreliability. In the conventional search techniques, we generally used chi-squarerandom variables for decision variables. Mathematically, a chi-square random variableis the sum of mutually independent, squared zero-mean unit-variance normal(Gaussian) random variables. With this base knowledge, we can separate decisionvariables to several normal random variables. We showed it with related equationsand conceptual diagrams. With this separation, we can improve the computationalefficiency of the process without losing the needed performance. If we averageseparated normal random variables sequentially, averaged values are also normalrandom variables. So we can use them as decision variables, which prevent from asudden increase of some decision variable. With the method using averaged decisionvalues, we can get the solution more quicklv and more reliably.To verify the performance of our proposed algorithm, we conducted simulations.We used some visual diagrams that are useful for intuitional approach. We analyzedthe performance of the proposed algorithm and compared it to the conventionalmethods.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2004.11a
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• pp.61-64
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• 2004

현재 GPS를 이용한 위성측위시스템은 기존의 DGPS에 의한 정밀도 향상 차원을 넘어 상시관측소를 활용한 기준국의 활용 증대 및 다양한 동시 사용자의 욕구를 충족시키기 위해 여러 가지 연구들이 진행되고 있다 현재 국내 연구동향으로 VRS-RTK (Virtual Reference Station Real Time Kinematic)에 대한 기초 연구가 진행 중에 있으며 해양수산부의 전파를 이용한 비콘 방식과 표준과학연구원 천문대에서는 MBC와 연계한 FM-DARC(Data Radio Channel)방식 등이 활용 방안으로 준비중에 있으며, 여러 기관과 대학 연구 기관에서 기초 연구가 진행 중에 있다. 따라서 이미 독일, 싱가폴, 일본 등에서 활용하고 있는 VRS의 연구를 보다 심화하여 현재 각기 다른 기관에서 보유하고 있는 70여개의 GPS 상시관측소의 효율적인 활용과 대 국민 서비스를 제공할 수 있는 시스템이 절실히 필요한 시기이다. 따라서 본 논문에서는 이런 가상관측의 결과를 산출할 수 있는 통계학적 모델링을 통한 가상관측 보정값을 산출할 수 있는 보정값을 제시할 수 있는 알고리즘 개발에 그 목적이 있다. 향후 알고리즘 개발이 완료되면 통계학적 모델링을 통해 단일 기준점에 의한 GPS 측량에서 불가능한 위치 결정 네트웍의 가상 관측을 가능하게 할 것이며, 신뢰성 있는 미지정수 해를 만들 수 있을 것이다.

• Journal of People, Plants, and Environment
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• v.24 no.4
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• pp.441-450
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• 2021

Background and objective: The purpose of study is to analyze the three-dimensional (3D) structure by creating a 3D model for green spaces in a park using unmanned aerial vehicle (UAV) images. Methods: After producing a digital surface model (DSM) and a digital terrain model (DTM) using UAV images taken in Mureung Park in Chuncheon-si, we generated a digital tree height model (DHM). In addition, we used the mean shift algorithm to test the classification accuracy, and obtain accurate tree height and volume measures through field survey. Results: Most of the tree species planted in Mureung Park were Pinus koraiensis, followed by Pinus densiflora, and Zelkova serrata, and most of the shrubs planted were Rhododendron yedoense, followed by Buxus microphylla, and Spiraea prunifolia. The average height of trees measured at the site was 7.8 m, and the average height estimated by the model was 7.5 m, showing a difference of about 0.3 m. As a result of the t-test, there was no significant difference between height values of the field survey data and the model. The estimated green coverage and volume of the study site using the UAV were 5,019 m² and 14,897 m³, respectively, and the green coverage and volume measured through the field survey were 6,339 m² and 17,167 m³. It was analyzed that the green coverage showed a difference of about 21% and the volume showed a difference of about 13%. Conclusion: The UAV equipped with RTK (Real-Time Kinematic) and GNSS (Global Navigation Satellite System) modules used in this study could collect information on tree height, green coverage, and volume with relatively high accuracy within a short period of time. This could serve as an alternative to overcome the limitations of time and cost in previous field surveys using remote sensing techniques.

• Journal of the Korean Association of Geographic Information Studies
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• v.25 no.4
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• pp.136-150
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• 2022

In this study, a comparative review was conducted on how to use RGB images to obtain river topographic information, which is one of the most essential data for eco-friendly river management and flood level analysis. In terms of the topographic information of river zone, to obtain the topographic information of flow section is one of the difficult topic, therefore, this study focused on estimating the river topographic information of flow section through RGB images. For this study, the river topography surveying was directly conducted using ADCP and RTK-GPS, and at the same time, and orthomosiac image were created using high-resolution images obtained by drone photography. And then, the existing developed regression equations were applied to the result of channel topography surveying by ADCP and the band values of the RGB images, and the channel bathymetry in the study area was estimated using the regression equation that showed the best predictability. In addition, CCHE2D flow modeling was simulated to perform comparative verification of the topographical informations. The modeling result with the image-based topographical information provided better water depth and current velocity simulation results, when it compared to the directly measured topographical information for which measurement of the sub-section was not performed. It is concluded that river topographic information could be obtained from RGB images, and if additional research was conducted, it could be used as a method of obtaining efficient river topographic information for river management.

• The Journal of the Korea Contents Association
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• v.7 no.11
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• pp.232-238
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• 2007

In this research, we constructed a 3D riverbed surveying system that is able to acquire the topographical information of a riverbed in real-time. The system consists of a RTK-GPS receiver and a echo sounder for collecting simultaneously the position and the water depth information of riverbed. A program for data composition and transformation was designed to generate the 3D coordinates by combining data of a GPS receiver and a echo sounder and made GIS database construction easy. We extracted TIN, digital elevation model and cross sectional maps of the riverbed by using GIS software from 3D data constructed through test surveying. It was shown that the accuracy of the result was RMS error of 0.069m when compared with the existing methods which use a total station and staffs. It is expected that the 3D riverbed surveying system wiil be able to be utilized to various surveying for water resources management in rivers, sea, dams, storing reservoirs and so forth.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.5
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• pp.379-388
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• 2019

Recently, a technique for acquiring spatial information data using UAV (Unmanned Aerial Vehicle) has been greatly developed. It is a very crucial issue of the GIS (Geographic Information System) mapping system that passes way point in the unmanned airframe and finally measures the accurate image and stable localization to the desired destination. Though positioning using DGPS (Differential Global Navigation System) or RTK-GPS (Real Time Kinematic-GPS) guarantee highly accurate, they are more expensive than the construction of a single positioning system using a single GPS. In the case of a low-priced single GPS system, the stability of the positioning data deteriorates. Therefore, it is necessary to supplement the uncertainty of the absolute position data of the UAV and to improve the accuracy of the current position data economically in the operating state of the UAV. The aim of this study was to present an algorithm enhancing the stability of position data in a single GPS mode of UAV with multiple GPS. First, the arrangement of multiple GPS receivers through the center of gravity of the UAV were examined. Next, MD (Mahalanobis Distance) is applied to detect instantaneous errors of GPS data in advance and eliminate outliers to increase the accuracy of previously collected multiple GPS data. Processing procedure for multiple GPS reception data by applying the center of the triangular method were presented to improve the position accuracy. Second, UAV navigation systems integrated multiple GPS through configuration of the UAV specifications were implemented. Using the unmanned airframe equipped with multiple GPS receivers, GPS data is measured with the TCM (Triangular Center Method). In addition, UAV equipped with multiple GPS were operated in study area and locational accuracy of multiple GPS of UAV with VRS (Virtual Reference Station) GNSS surveying were compared. The result showed that the error factors are compensated, and the error range are reduced, resulting in the reliability of the corrected value. In conclusion, the result in this paper is expected to realize high-precision position estimation at low cost in UAV using multiple low-cost GPS receivers.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.691-695
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• 2012

수위표의 영점에서 수면까지의 높이로 정의되는 해발수위는 유량 및 유사량 등과 같은 관련 수문자료를 생산하는데 기본이 되는 자료이며, 하천 및 수공구조물의 설계 등에 기초자료로 이용될 뿐만 아니라 수자원의 효율적인 관리 및 수문순환 해석을 위한 가장 중요한 기초자료로서 국가 차원의 올바른 수자원 계획과 정책을 수립하는데 널리 활용된다. 이와 같이 해발수위자료의 이용 분야가 다양하고 그 자체로서도 중요한 의미를 가지는 점을 고려할 때 무엇보다도 중요한 것은 자료의 품질이 확보되어야 하는 것이다. 그러나 영점표고검정수준점 및 기준 수위표의 설치 이후 오랜 시간이 경과됨에 따라 노후화와 수위관측소 주변의 환경변화가 발생하게 되어 자료의 정확도가 매우 낮아지고 있다. 본 연구에서는 해발수위 자료의 품질향상을 위해 수위관측소의 영점표고검정수준점 및 수위표 영점표고에 대하여 수준측량 및 RTK(Real Time Kinematic) GPS(Global Positioning System) 측량을 병행하여 수행하였으며, 조사측량된 값을 활용하여 기존에 측량된 영점표고검정수준점 및 수위표 영점표고에 대한 검토를 수행하였다. 금강 및 삽교천 수계에 위치한 50개 수위관측소 대하여 기존 측량값과 비교 검토한 결과 영점표고검정수준점은 0.10m 이하(54.0%), 0.10m 초과 ~ 0.50m 이하(26.0%), 0.50m 초과 ~ 1.00m 이하(6.0%), 1.00m초과 ~ 1.50m 이하(2.0%), 1.50m 초과 ~ 2.00m 이하(2.0%), 2.00m 초과 ~ 3.00m 이하(4.0%), 3.00m 초과(6.0%)의 값을 나타냈으며, 수위표 영점표고는 0.10m 이하(50.0%), 0.10m 초과 ~ 0.50m 이하(32.0%), 0.50m 초과 ~ 1.00m 이하(10.0%), 1.00m초과 ~ 1.50m 이하(2.0%), 1.50m 초과 ~ 2.00m 이하(2.0%), 2.00m 초과 ~ 3.00m 이하(2.0%), 3.00m 초과(2.0%)의 값을 가졌다. 이와 같이 기존과 금회 측량자료를 비교 검토한 결과 대부분이 안정적으로 유지되고 있으나 일부 수위관측소에서 변동량이 크게 발생한 원인은 영점표고검정수준점의 노후화, 기준 수위표의 교체 및 위치 변동, 인위적인 하천공사 등으로 인하여 발생한 것으로 판단된다.