Yong-Cheol Suh

Evaluation of Satellite-Based Navigation Services in Complex Urban Environments Using a Three-Dimensional GIS

We developed a comprehensive simulation system for evaluating satellite-based navigation services in highly built-up areas; the system can accommodate Global Positioning System (GPS) multipath effects, as well as line-of-sight (LOS) and dilution of position (DOP) issues. For a more realistic simulation covering multipath and diffracted signal propagations, a 3D-ray tracing method was combined with a satellite orbit model and three-dimensional (3D) geographic information system (GIS) model. An accuracy estimation model based on a 3D position determination algorithm with a theoretical delay-locked loop (DLL) correlation computation could measure the extent to which multipath mitigation improved positioning accuracy in highly built-up areas. This system could even capture the multipath effect from an invisible satellite, one of the greatest factors in accuracy deterioration in highly built-up areas. Further, the simulation results of satellite visibility, DOP, and multipath occurrence were mapped to show the spatial distribution of GPS availability. By using object-oriented programming, our simulation system can be extended to other global navigation satellite systems (GNSSs) simply by adding the orbital information of the corresponding GNSS satellites. We demonstrated the applicability of our simulation system in an experimental simulation for Shinjuku, an area of Tokyo filled with skyscrapers.

Ajax GIS application for GNSS availability simulation

This paper describes an Ajax (Asynchronous JavaScript and XML) GIS (geographic information system) application for the simulation of GNSS (Global Navigation Satellite System) availability in dense urban areas. In the forthcoming GNSS environment, satellite visibility will be greatly increased owing to the integration of multiple GNSSs such as the American GPS (Global Positioning System), the Russian GLONASS (Global Navigation Satellite System), the European Union’s GALILEO, and the Japanese QZSS (Quasi-Zenith Satellite System). However, in dense urban areas, the improvements of position accuracy may be limited because obstruction of the signal by high buildings results in bad geometries and multipath effects. To evaluate the spatiotemporally varying availability of GNSS positioning, we built an estimation model that computes the number of visible satellites, the values of DOP (dilution of position), and the amount of multipath errors, according to the location and time of a user. Then, the GNSS availability components were visualized in an Ajax-based Web application that provides a desktop-like interactiveness through the asynchronous data transfer between client and server. This Web simulation shows when and where the navigation services by integrated GNSS are available or appropriate in urban canyons. As a feasibility test, we demonstrated an experimental simulation for the Shinjuku ward of Tokyo filled with skyscrapers.

Development of an RTK-GPS Positioning Application with an Improved Position Error Model for Smartphones

This study developed a smartphone application that provides wireless communication, NRTIP client, and RTK processing features, and which can simplify the Network RTK-GPS system while reducing the required cost. A determination method for an error model in Network RTK measurements was proposed, considering both random and autocorrelation errors, to accurately calculate the coordinates measured by the application using state estimation filters. The performance evaluation of the developed application showed that it could perform high-precision real-time positioning, within several centimeters of error range at a frequency of 20 Hz. A Kalman Filter was applied to the coordinates measured from the application, to evaluate the appropriateness of the determination method for an error model, as proposed in this study. The results were more accurate, compared with those of the existing error model, which only considered the random error.

Frequent Unscheduled Updates of the National Base Map Using the Land-Based Mobile Mapping System

This paper focuses on the use of the Land-based Mobile Mapping System (LMMS) for the unscheduled updates of a National Base Map, which has nationwide coverage and was made using aerial photogrammetry. The objectives of this research are to improve the weak points of LMMS surveying for its application to the updates of a National Base Map (NBM), which has rigorous accuracy and quality standards. For this, methods were suggested for the (1) improvement of the accuracy of the Global Positioning System/Inertial Navigation System (GPS/INS) in the long-term exposure of environments with poor GPS reception; (2) elimination of mutual deviations between LMMS data obtained in duplicate to meet resolution standards; (3) devising an effective way of mapping objects using LMMS data; and (4) analysis of updatable regions and map layers via LMMS. To verify the suggested methods, experiments and analyses were conducted using two LMMS devices in four target areas for unscheduled updates of the National Base Map.

A New Window-Based Program for Quality Control of GPS Sensing Data

The main purpose of this study is to develop a new Windows-based program that calculates a quality control parameter that shows the quality of GPS observations using Global Positing Sensing (GPS) data in a Receiver INdependent Exchange (RINEX) format. This new program, Global Positing Sensing Quality Control) (GPSQC), allows general GPS users to easily and intuitively check the quality of GPS observations before post-processing, which will lead to the improvement of GPS positioning precision in diverse areas of GPS applications. The GPSQC is designed to control the multi-path, cycle slip, and ionospheric errors of L1 and L2 signals in GPS observations. The GPSQC was developed using C#.NET language for the Window series with Microsoft Graphical User Interfaces (MS GUIs). This program gives brief information for GPS observations, time series plots, graphs of quality control parameters, and a summary report in MS word, Excel and PDF formats. It can simply perform quality checking of GPS observations that is difficult for surveyors conducting field work. We expect that GPSQC can be used to improve the accuracy of positioning and to solve time-consuming problems due to data loss and large errors in GPS observations.

Development of Soil Compaction Analysis Software (SCAN) Integrating a Low Cost GPS Receiver and Compactometer

A software for soil compaction analysis (SCAN) has been developed for evaluating the compaction states using the data from the GPS as well as a compactometer attached on the roller. The SCAN is distinguished from other previous software for intelligent compaction (IC) in that it can use the results from various types of GPS positioning methods, and it also has an optimal structure for remotely managing the large amounts of data gathered from numerous rollers. For this, several methods were developed: (1) improving the accuracy of low cost GPS receiver’s positioning results; (2) modeling the trajectory of a moving roller using a GPS receiver’s results and linking it with the data from the compactometer; and (3) extracting the information regarding the compaction states of the ground from the modeled trajectory, using spatial analysis methods. The SCAN was verified throughout various field compaction tests, and it has been confirmed that it can be a very effective tool in evaluating field compaction states.

The Inference Search Process for Managing Control Points Using OWL and SWRL

Current searching works are common and essential in Web users. On the other hand, in the real world, the searching is the time-consuming works because of several searching to extract more exact and satisfied information. In this paper, we propose an Inference process to effectively extract control points based on the ontology. The ontology-based searching supports hierarchical and associated results as well as knowledge sharing with hierarchy concepts. Moreover, inferred searching can lessen consumed times of searching and prevent empty results with ontology and user-defined reasoning rules.