10.2 A GPS Glossary

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Here are some GPS terms that you will encounter when you use GPS and GPS software:


8/12 channels receiver

An 8-channel receiver uses 8 channels to access 8 different satellites at any one time. A 12-channel receiver can access 12 satellites at once.


Bearing

The direction you are aiming for.


CEP, RMS, and 2D RMS

Circular Error Probable (CEP), Root Mean Square (RMS), and 2D RMS are all measures of the accuracy of a GPS receiver. CEP represents the radius of a circle containing 50% of the GPS readings. RMS represents the radius of a circle containing 68% of the GPS readings. 2D RMS represents the radius of a circle containing 98% of the GPS readings. If three GPS receivers each claims to have 2m CEP, 2m RMS, and 2m 2D RMS respectively, then the third one is the most accurate, because it has readings accurate to within a 2-meter radius 98 percent of the time.


DGPS

Differential GPS is an enhancement to the satellite-based GPS that makes use of receivers on fixed reference points on the ground and improves accuracy to within 3-5 meters . These receivers transmit error-correcting information to DGPS receivers to enhance the information supplied by the satellites.


Fix

A location returned by the GPS receiver after processing the readings of at least three satellites.


Heading

The actual direction you are traveling towards. It is not the same as bearing. Bearing is your desired direction, but you may not be heading towards the desired direction due to factors such as obstacles (e.g., water, fences, and mountains ). Therefore, you have to momentarily head in another direction in a bid to get to your destination.


Latitude, longitude, and altitude

The coordinates of a specific location on earth. These three pieces of information together define a point in the three-dimensional space.


National Marine Electronics Association (NMEA)

The NMEA-0183 standard has been universally adopted by GPS manufacturers and virtually every GPS product for exchanging navigational information between devices. NMEA-0183 defines a " sentence " format (using printable ASCII text) describing navigational information.


Route

A collection of waypoints representing the path that you would like to take.


Selective Availability (SA)

The degradation of GPS data for nonmilitary use. See the sidebar "GPS Accuracy" earlier in this chapter for more information on SA.


Time to First Fix (TTFF)

The least amount of time required to obtain a fix by the minimum number of satellites required for triangulation. Normally, it takes a few minutes before you can receive a fix.


WAAS

WAAS is an enhancement similar to DGPS that uses fixed reference stations on the ground to enhance accuracy to under 3 meters.


Waypoint

A location that you store in your GPS system (as coordinates). Examples of waypoints are a hiking location, camping ground, church , or any place of interest to a GPS user . You normally add a waypoint to your GPS before you start your traveling. You can also add one during your travel when you locate a place of interest.

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Linux Unwired
Linux Unwired
ISBN: 0596005830
EAN: 2147483647
Year: 2004
Pages: 100

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