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GPS AND AVL Tracking
Global
Positioning System (GPS)
GPS is a satellite-based radio navigation system developed and operated by the U.S. Department of Defense. GPS permits land, sea, and airborne users to determine their three dimensional position, velocity, and time, 24 hours a day in all weather, anywhere in the world.
GPS consists of
three segments: space, control, and user.
The GPS concept
of operation is based upon satellite ranging. Users figure their position on the
earth by measuring their distance from the group of satellites in space. The
satellites act as precise reference points.
Each GPS
satellite transmits an accurate position and time signal. The user's receiver
measures the time delay for the signal to reach the receiver, which is the
direct measure of the apparent range to the satellite. Measurements collected
simultaneously from four satellites are processed to solve for the three
dimensions of position, velocity and time.
GPS receivers collect signals from satellites in view. They display the user's position, velocity, and time, as needed for their marine, terrestrial, or aeronautical applications. Some display additional data, such as distance and bearing to selected waypoints or digital charts.
GPS is used to
support land, sea, and airborne navigation, surveying, Geophysical exploration,
mapping and geodesy, vehicle location systems, and a wide variety of additional
applications.
GPS provides
two levels of service -- a Standard Positioning Service (SPS) for general public
use and an encoded Precise Positioning Service (PPS) primarily intended for use
by the Department of Defense. SPS signal accuracy is intentionally degraded to
protect U.S. national security interests. This process, called Selective
Availability (SA), controls the availability of the system's full capabilities.
The SPS accuracy specifications, given below, include the effects of SA.
SPS provides
accuracy's of (for position, the accuracy with respect to geographic, or
geodetic coordinates of the Earth) within:
100 meters (2
drms) horizontal 156 meters (2 Sigma) vertical 300 meters (99.99% prob.)
horizontal 340 nanoseconds time (95% prob.)
SPS Coverage is
continuous and worldwide, with a position dilution of precision (PDOP) of 6 or
less.
GPS based Automatic Vehicle location or tracking systems let a viewer observe the GPS-determined position of a person or vehicle from a remote location at a given time. GPS tracking has been available for several years, and has been used by very large firms to track assets such as trucks and trailers. The ideal tracking system would be small, low cost and easy to install. However, the technology is still evolving, and most systems are expensive and require the incorporation of several larger, more obtrusive devices. Personal tracking devices that are available are few, and they are not yet small enough to be convenient for use on the people with the greatest need.
The
primary components of the GPS based AVL system are:
1) a GPS receiver, with power and a
data connection.
2) a communication device, such as a
cell phone, wireless device, radio or satellite transmitter.
(Sometimes items 1
& 2 are integrated into a single device)
3) a communication service for the
device.
4) an on-line tracking service or
centralized tracking software for a PC with a modem.
Selection
of tracking system components is dependent upon several factors:
1) the area where you are tracking
your asset within.
2) service availability for the
communication device that you choose
3) the type and frequency of data
you wish to collect or communicate
4) the number of assets you wish to
track
5) the type of equipment you may already
have
6) where you need to access the tracking
data from
7) the budget, and the cost/benefit
of the tracking.
8) the addition of other functions, such as
navigation or two-way communication.
Real Time Tracking. The GPS receiver will compute its position based on data it receives from GPS satellites. When a position report is requested, the base tracking station issues a call via its communication service to the communication device attached to the GPS receiver. If the GPS device has power, and can see the satellites, it will transmit back position (and sometimes other) information. If the satellite view is blocked, sometimes the GPS will transmit the last known position. If the asset is outside the range of the communication network, then no position reading can be successfully reported.
Another form of tracking device is a passive tracker. This device does not transmit real-time tracking information. Instead the GPS antenna feeds regular location, speed and time information into internal memory, which is later downloaded for analysis, using a program the customer has on their PC. These are useful to keep records of where the vehicle has been, and time in transit. Usually these are wired to the vehicle power system, though some have internal batteries (with limited operating time).
Different users may demand different tracking needs.
Depending upon the system components you choose, you may be able to have your tracking system function in the following ways to meet your needs:The largest group of users is the trucking industry. Transcontinental and regional carriers both benefit by knowing the location of their cargo at any point in time. It can help you identify delays or forecast arrival times, plus you can be better able to re-direct drivers to pick up additional loads in-transit, or for return legs. Most of these users require satellite tracking, unless the region is completely within the service territory of the radio, wireless or cellular network.
Many smaller fleets of local delivery and repair trucks and emergency vehicles can be found in the major metropolitan areas. These assets can usually take advantage of service coverage provided by the public cellular or wireless network. These customers can use real-time tracking, usually on demand, to find assets when the need arises. Incorporating a mapping GPS into the system may help drivers reach their destinations more quickly.
For Heavy Industries like Petrochemicals,Steel,Coal etc, a private radio network (VHF\UHF) is used.
Owing to cost implications in sending the data , event based tracking is sometimes used. This means that the AVL system only transmits the data, when a exception occurs i.e. when the vehicle strays from its designated path or when it does not reaches it schedule destination on time etc. This saves the data transmission costs.
Tracking Costs associated with tracking systems vary with the needs of the company and which system components you choose to meet those needs. In general, there is
a) the cost of the GPS and communication hardware (and attachments)
b) the cost of the communication service.
c) the cost for tracking software or service
d) Installation and Commissioning costs
e) Training costs for the dispatcher or system operator
In general, tracking system costs range from about $800 per vehicle for simpler systems, up to about $1500 per vehicle, for more complicated or far-reaching systems, plus any associated monthly fees.| Sl No. | Item | Manufacturer |
| 1 | Garmin GPS V | www.garmin.com |
| 2 | Radio Modem with 0.5 w telemetry module | www.woodanddouglas.co.uk |
| 3 | VHF radios- Motorola GM300/950 | www.Motorola.com |
| 4 | GIS Mapping software(FREE) | www.agismap.com |
| 5 | Tracking software | Fugawi software, Manufacturer Northport, used with Navtech GPS. |
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