25-02-2013, 11:32 AM
Navigation Systems
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INTRODUCTION
What is navigation? From, time immemorial human beings relied on
natural signpost and the position of celestial bodies to find the desired route.
As the population increase the need for better transportation increase. With the
increase in automobiles came the problem of traffic congestion. This led to
research in the field of navigation engineering. This brought about a wave of
technological breakthroughs.
In this report I have included the major navigation systems such as GPS
aided navigation system, two-dimensional vehicle tracking using video image
processing, the position location arid reporting system used by the US Army
and Marine Corps. Neural networks structure can be used to automate high
way driving.
AN INFORMATION STRUCTURAL MODEL OF
VEHICLE NAVIGATION AND ITS IMPLICATIONS
This paper proposes a simple model to provide a framework for
investigating human behavior with vehicle navigation aids. This model
consists of planning, decision- making, control, and perception. Decisions are
made by comparing perceived cues from the outside view with the expected
cues from planning. VNA assist mainly in dynamic planning, providing
support and updating to the cognitive map, navigators have of their
environment.
VNA aims at assisting drivers in car navigation; human capabilities and
limitations have to be incorporated in VNA designs. To date research in
vehicle navigation has not provided sufficient models to support such designs.
There are many aspects of vehicle navigation with VNA have not been
intensively addressed with models. The interactions between the human
driver, the machine and the natural view of the environment is one of them.
A VNA system is assumed to have at least the following Characteristics
1. It has a database of navigation information. The database provides
geographical and other relevant information about the area that the
vehicle is traveling through.
2. It has a capability of locating the current position of the vehicle.
3. There is an algorithm making dynamic suggestions on route selection.
4. It has an interface, which presents the navigation model to the human
driver.
DEVELOPMENT OF ADVANCED DYNAMIC
NAVIGATION SYSTEM
The dynamic navigation system is an information providing type
navigation and route guidance system. Fundamentally the system is suited for
phased implementation. In the information providing system, travelers can
obtain traffic condition information and determine travel routes at their own
discretion. Thus it may satisfy travelers more than an infrastructure oriented
perceptive system, thus achieving a higher acceptance ratio for the information
provided.
WHEEL ODOMETERS
Wheel odometers measure the vehicle traveling distance by multiplying
the number of pulses, electronically generated by the rotating wheels by a
constant, which depends on the perimeter of the wheels. Factors such as
vehicle speed, tire pressure, vehicle payload, tire tread wear off, etc. all affect
the actual tire size and thus the distance measurement accuracy.
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The difference between distance measurements from both the left and
the right wheels when it is small is in proportion to the relative heading. This
property makes the odometers useful for measuring the vehicle heading as
well. In reality, however, the measurement accuracy of relative heading is
affected by the distance measurement errors. However difference exists
between left and right wheel distance measurements. The distance difference
translates into a drift in bearing measurement even when the vehicle is
traveling on a straight road. Using the bias bearing measurements, the deadreckoning
trajectory eventually arrives at a distant point that is significantly
different from the point of destination. This drifting phenomenon is a major
error source for the dead-reckoning systems using differential odometry.
FLUX GATE COMPASS
Flux gate compass uses a pair of perpendicular coils to measure the
direction of the magnetic field. By measuring the vector direction formed by
the two coil voltages, the direction of the magnetic field can be determined.
Since the vehicle is a steel structure, the actual magnetic field direction,
measured by an onboard compass is really from the combined magnetic field
formed by the earth and the vehicle itself. The accuracy of the compass
measurements is thus affected greatly by the degree of vehicle body
magnetization.
A commonly used method to calibrate the magnetization effect is to
turn the vehicle for 360 0 and obtain the minima and maxima for both coil
voltages to identify the center of the magnetization circle. In addition, the
vehicle magnetic field may be affected by steel items carried on the vehicle,
the electrical current generated by onboard electrical devices etc.