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| GPS Terminology |
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What is a Waypoint ?
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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.
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What is the difference between bearing and heading ?
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'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 ?
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A route is a
series of waypoints entered in the order that you want to navigate them.
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What is TTFF ?
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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 ?
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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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