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GNSS (Global Navigation Satellite System) has been effectively used in civil aviation, maritime transportation as well as other fields due to its stability, convenience, and high accuracy. Different from other land-based application, railway transportation is relatively fixed on rail tracks. This makes digital track map a vital basis for introducing GNSS into railways. First of all, the digital track map provides the representation of both geometry and topology of the railway tracks. Also, it creates the connection between three-dimensional position coordinates and one-dimension track-defined location for the train. SIS (Signal in Space) unavailability and multipath problem often challenges GNSS-based train positioning because of the environment diversity (such as canyon, bridge, mountain and so on) along the track. However, the digital track map can be integrated as an assistance for train location determination system, which can greatly improve the performance in terms of availability, accuracy and integrity. The digital track map is divided into two parts in this paper: geometry structure and topology structure, and the requirements of each part is analyzed. The horizontal geometry of a rail track is usually consisted of three segments: straight lines, circular curves and transition curves, where cubic parabola or clothoid is frequently used. The topological railway network represents the topological connections such as signaling, switch and block design, which are important elements in train control system. In this paper we propose a method to identify mainline track geometry, then different approximation methods are adopted to present different segments of the track, which makes a better description of track instead of many consecutive points only. Then the points-of-interest (POIs) and sidings are added as topological information of the railway network. Furthermore, the evaluation of the geometry and topology of the generated track map is detailed afterwards. Finally, the field data in real railway line is used to generate the digital track map and the result shows the proposed method can effectively identify the mainline geometry and present the topology network correctly without too much storage.

Precise point positioning (PPP) is increasingly being used in many precise positioning applications, which can provide centimeter-to-decimeter-level accuracy with using a single receiver and not be dependent on differential correction. As the railways in China’s western region have the characteristics of long mileage, low traffic volume and inadequate infrastructure, PPP results not only further improve the positioning accuracy without the limitation of the operation range, but lower set-up and maintenance cost at the same time. In order to obtain more information of train location, one widely used solution to deliver a more consistent position, speed and attitude is the integration of GNSS and Inertial Navigation System (INS). However, GNSS signals cannot be always maintained in difficult areas such as bridges, tunnels and valleys, the performance of the GNSS/INS integrated navigation system therefore degrades greatly because of the gyroscope and accelerometer errors. Fusing the wheel speed sensor and the Inertial Measurement Unit (IMU) data is one of the most efficient way to provide train position in GNSS signal outage area. In this research, we focus on the PPP performance for train kinematic positioning computed by the different International GNSS Service (IGS) products, and propose a feasible PPP-GNSS/INS/wheel speed sensor integrated navigation system. In order to evaluate the performance of the proposed train positioning system, a real experiment was conducted on the Qinghai-Tibet railway in western China. Compared with the measurements of Differential Global Positioning System (DGPS), the RMS value of PPP-GNSS/INS/wheel speed sensor integrated navigation positioning results computed by IGS final products are 0.7549m, 0.6053m and 1.7454m in north, east, and vertical direction, respectively. It is interesting to note that the accuracy of integrated navigation positioning results computed by the IGS Rapid products is compared with that computed by the IGS Final products, while the performance of positioning results computed by IGS Ultrarapid products is unsatisfied owing to the errors of predicted satellite clocks and orbits. Also, the experimental results indicate that the PPP-GNSS/INS/wheel speed sensor integrated navigation system could provide accurate and continuous positioning results in both open-sky and GNSS signal-obstructed environments.

The train positioning technology based on GNSS (Global Navigation Satellite System) has greatly developed in the train control system because of its stability, low-cost, easy maintenance. The train positioning technology is used to prevent possible potential train-to-train collision, and it can also be utilized for automatic train operation and train scheduling. However, due to some inevitable defects in GNSS, such as SIS (Signal in Space) unavailability, multi-path effects and electromagnetic interference and so on, map-assisted train positioning technique is proposed to achieve a better performance. Map matching plays a crucial role in map-assisted train positioning, which uses position and heading data from positioning systems including GNSS, dead reckoning (DR) system and inertial navigation system (INS) to integrate and then compare with the track map database. The map matching algorithm finally distinguishes the actual track the train is running on between parallel tracks and matches the measured position to the right point on map route. So a digital track map database is indispensable for map-assisted GNSS-based applications. The track map database can be built based on the original measurements with high-accuracy GPS receivers. And developing a dedicated tool to assist map data collection and processing in field operation is of great importance, which can reduce the cost and workload considerably. In this paper, the requirements and necessities of digital track map database in train positioning are explained. The map-tool-chain is implemented, which consists of Station Schematic Editor, Station Map Data Recorder, Map Database Editor, and Map Database Validator. The four components serves the whole process of the generation of digital track map database, which includes four step: railway track surveying, data processing, map database generation and map database validation. There are a lot of methods using during the track map generation, such as outliers elimination in original measurement, uniform sampling, smoothness inspection in track curve and multiple GPS trajectories fusion. These algorithms will be elaborated in this paper. Furthermore, the map-tool-chain is used to generate a track map database for field applications in Hankou-Yichang Railway (HYR) and Jincheng Anthracite Mining Group in China. The results from field applications prove that the map-tool-chain can not only inspect and remove the outliers in raw data, but also make the generated track map better spacing and smoother. The proposed methods and map-tool-chain will be more competitive in developing rail applications based on GNSS positioning, including train control and supervision system, train collision early warning system and train integrity monitoring system.