Integrated Systems and their Impact on the Future of
Positioning, Navigation, and Mapping Applications
by Naser El-Sheimy
Key words: GPS, Inertial Systems, Navigational Aid,
Vision-Based Systems.
Abstract
The Global Positioning System (GPS) is a
constellation of satellites that broadcast signals that can be used to
derive precise timing, location, and velocity information. The derived
information (time, position, and velocity) may be combined with other
systems such as communications devices, computers, and software to
perform a variety of tasks.
The Global Positioning System (GPS) is capable of
providing all range positioning accuracy in all situations where
uninterrupted signal reception is possible and the general satellite
geometry is within acceptable limits. It is also evident that other
navigation technologies, such as Inertial Navigation Systems (INS),
are currently not capable of providing similar accuracies at a
comparable price, i.e. there is no real competition to GPS in a
scenario of uninterrupted signal reception. This leaves two scenarios
to be considered. The first one is that of intermittent signal
reception, as for instance in heavily forested areas or in urban
centres. The other one is that of no signal reception at all, as for
instance in buildings, underground or underwater. In the first case,
GPS has to be integrated with other sensors to bridge periods of no
signal reception. In the second case, GPS has to be replaced by
another system that can provide continuous navigation in those
environments where GPS does not work. Both cases will be treated in
this paper where the integration of systems and navigational aids (navaids),
will be investigated as an alternative for times of no GPS signal
reception. In terms of systems, both INS and vision-based systems will
be considered. In terms of navaids, odometers, gyros and digital maps
will be considered for land vehicle navigation, and pedometers,
magnetic compasses, digital maps, and cellular phones for backpack
systems.
Integrated systems will, therefore, provide a
system that has superior performance in comparison with either a GPS,
an INS, or vision-based stand-alone system. For instance, GPS derived
positions have approximately white noise characteristics over the
whole frequency range. The GPS-derived positions and velocities are
therefore excellent external measurements for updating the INS and
providing the imaging sensors with position parameters, thus improving
its long-term accuracy. Similarly, the INS can provide precise
position and velocity data for GPS signal acquisition and
reacquisition after outages and the orientation parameters for the
vision-based system. The vision-based system can be used as a backup
navigation system and to update the INS data if the GPS signal is
blocked for long periods. In general, the fact that redundant
measurements are available for the determination of the vehicle
trajectory parameters greatly enhances the reliability of the system.
The paper will cover both, the concept of
integration and implementation aspects of integrated systems. Features
common to most systems will be identified and factors affecting system
performance will be discussed. All major features will be illustrated
by examples. Finally, examples on future systems for mapping,
positioning, and navigation applications will be given.
Dr. Naser El-Sheimy
Assistant Professor
Chair FIG C5 WG 1
Department of Geomatics Engineering
The University of Calgary
2500 University Dr.
N.W. Calgary
Canada
E-mail: naser@geomatics.ucalgary.ca
Web: http://www.geomatics.ucalgary.ca/~nel-shei/
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