Vehicle GPS tracking systems for Moving Vehicles

NRL collects the GPS data along with the laser tracking data for inter comparison studies. Tracking data from the GPS Control Segment stations, USNO, the broadcast position data and DMA precise ephemerides are collected. These are continuous data over the in~rbit operation of the satellites. To utilize the GPS derived tracking data for inter comparison with the laser derived data, the local clocks at the GPS Monitor Station sites must be accounted for since they are the basis for the GPS tracking measurements. In GPS itself these clocks are accounted for by the use of GPS Time which is a common synchronization time computed at the MCS. However, the GPS ranging measurements are directly related to the local clocks whose performance must be removed if the satellite clock is to be isolated from the satellite orbital position and evaluated. The laser data is independent of this influence on ranging measurements since the local clock is used for time tagging.

To determine the performance of the station clocks to the Master clock at USNO, common view time comparisons with USNO were made to the Colorado Springs, Hawaii and Ascension stations. Navigation users would not be aware of these changes since they use GPS Time which is a computed time accounting for these changes. For this experiment, removal of the local clock and the satellite position error by laser derived positions from the GPS tracking data will leave the satellite clock as the principal error component.

The field testing of VISAT, a prototype mobile highway mapping system which has been developed in cooperation between the University of Calgary and Geofit Inc. in Laval, Quebec, is described in this paper. The integration of inertial technology and GPS satellite receivers with an array of ceo cameras ( camera rear view mirror ) has resulted in a system that is capable of mapping all visible objects within a 50 m radius of the moving vehicle. Extensive tests in city centers, suburban areas, and rural areas have shown that the system works very reliably and that the expected positioning accuracy of 30 cm is surpassed in many cases. A more detailed analysis of the results shows that the RMS positioning error in acrosstrack direction and height is actually between 5 and 10 cm, while the along-track error is usually larger. Due the restrictions in the length of the paper, only some of the major results can be highlighted.

VISAT system integrates a cluster of video cameras ( rearview mirror with camera , Android rear view camera ), an Inertial Navigation System (INS), and satellite receivers of the Global Positioning System (GPS). The system carrier is currently a van, but airborne or marine applications can be realized in a similar way. The overall objective of the VISAT development was to build a precise multi-sensor mobile mapping system that could be operated at speeds of up to 60 Ian per hour and would achieve an accuracy of 0.3 m (RMS) with respect to the given control and a relative accuracy of 0.1 m (RMS) for points within a 50 m radius. This accuracy is required in all environments including inner cities, where stand-alone GPS is not reliable. Accuracy optimization must therefore be done with a view to total system performance, while system design has to be optimized with a view to isolating the error contribution of each sensor. The data flow has to be streamlined to facilitate the subsequent feature extraction process and transfer into a GIS system.