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MacFixer, the iPhone, iPod, and iPad specialists
GPS Terminology

 

What is a Waypoint ?

Waypoints are locations or landmarks worth recording and storing in your GPS. These are locations you may later want to return to. They may be check points on a route or significant ground features. (e.g., camp, the truck, a fork in a trail, where Charlie buried his treasure,).

Waypoints may be defined and stored in the unit manually, by taking coordinates for the waypoint from a map or other reference. This can be done before ever leaving home. Or more usually, waypoints may be entered directly by taking a reading with the unit at the location itself, giving it a name, and then saving the point. Waypoints may also be put into the unit by referencing another waypoint already stored, giving the reference waypoint, and entering the distance and compass bearing to the new waypoint.

 

 

What is the difference between bearing and heading ?

'Bearing' is the direction you are aiming at while 'heading' is the direction you are actually going. Sometimes they are the same but sometimes you can't head directly where you want to go because of fences, wind, road, and other reasons. Heading is sometimes called 'track' so there are three words in use to describe these things. When flying you can actually point the plane in one direction while flying in another (due to wind) and neither may actually be toward the final destination (due to mountains).

 

 

What is a Route ?

A route is a series of waypoints entered in the order that you want to navigate them.

 

 

What is TTFF ?

TTFF stands for Time To First Fix.  This is the amount of time it takes to get a complete fix on as many satellites as it requires to triangulate your position.

 

 

8 or 12 Channel Receivers ?

The number of channels used by your GPS receiver is directly related to the number of satellite transmissions it can interpret at once. For example, if you have an 8 Channel receiver, then you can access eight different satellites at once. A 12 Channel receiver can interpret signals from twelve satellites. This is important if accuracy and consistency is a prime concern.

 

What is WAAS ?

WAAS stands for Wide Area Augmentation System.  WAAS is a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy.  A WAAS-capable receiver can give you a position accuracy of better than three meters, 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.  WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

 

Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of WAAS is that it does not require additional receiving equipment while DGPS does.

 

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