Saturday, August 27, 2011

All about GPS

The Global Positioning System (GPS) is a satellitebased
navigation system that provides reliable
positioning, navigation, and timing services

GPS shows the exact position on earth

GPS is a constellation of 24 satellites revolving
11,000 nautical miles above earth surface

A GPS receiver can detect signals transmitted by GPS sattelites

Terminologies
Differential GPS (DGPS)
• DGPS is a method of improving the accuracy of your receiver by
adding a local reference station to expand the information
available from the satellites

Wide Area Augmentation System (WAAS)
• WAAS is intended to enable aircraft to rely on GPS for all phases
of flight, including precision approaches to any airport within its
coverage area
• It transmits signals containing information on reliability and
European Geostationary Navigation Overlay
Service (EGNOS)accuracy of the positioning signals which are sent by GPS and Global Orbiting Navigation Satellite system(GLONASS)

Local Area Augmentation System ( LAAS)
• Corrected data are transmitted from a local source, typically an
airport or another location where accurate positioning is needed
• These correction data are typically useful for only about a thirty to
fifty kilometer radius around the transmitter

Geometric Dilution of Precision (GDOP)
• The effects of the combined errors of four variables (latitude,
longitude, altitude, and time) on the accuracy of a threedimensional
fix
• The ratio of incoming signal strength to the amount of interfering
Signal to Noise Ratio (SNR)
noise as measured in decibels on a logarithmic scale.

# Gpsd-GPS Service Daemon
gpsd is a service daemon that monitors one or more GPSs attached to a
host computer through serial or USB ports
It makes all data on the location/course/velocity of the sensors,
available to be queried on TCP port 2947 of the host computer
With gpsd, multiple GPS client applications (such as navigational and
wardriving software) can share access to GPSs without contention or
loss of data
# Waypionts
A waypoint is a spot on the surface of the Earth as defined by
coordinates that are inputted into the GPS and stored, usually along
with an icon, a descriptive name, and some text

Websites where waypoints can be stored:
• www.waypoint.org
• www.swopnet.com/waypoints
• www travelbygps.com
• www.pickatrail.com

#Wardriving
Wardriving is an activity by which WiFi
networks, broadcasting signals are
detected

With addition of GPS, pinpoint location
of the discovered hotspot can be stored

Information regarding street names,
building numbers, network spots, and
logs by location are stored automatically

#Sources of GPS Signal Errors

Factors which reduce quality of GPS signal are:
1.Ionosphere and troposphere delays
2.Signal multipath
3.Receiver clock errors
4.Orbital errors
5.Number of satellites visible
6.Satellite geometry/shading
7.Intentional degradation of the satellite signal

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