Eagle journey User Guide
11
to calculate a position. Speed, direction of travel, and distance are all
calculated from position information. Therefore, in order for it to determine
direction of travel, you must be moving and the faster, the better. This is
not to say that it won’t work at trolling speeds - it will. There will simply be
more “wandering” of the data shown on the display.
calculated from position information. Therefore, in order for it to determine
direction of travel, you must be moving and the faster, the better. This is
not to say that it won’t work at trolling speeds - it will. There will simply be
more “wandering” of the data shown on the display.
The United States government used to intentionally degrades the satellite’s
signal for civilian users. They introduced small errors into the signals that
made the GPS receiver less accurate. These errors are called selective
availability, or SA. This made the position reported by a GPS receiver that
met their specification to be within 100 meters horizontally and 150 meters
vertically 95% of the time. (The position can be worse than that the other
5% of the time.) In other words, the position shown on your receiver was
within 100 meters of your actual position, 95% of the time. That’s over 300
feet!
signal for civilian users. They introduced small errors into the signals that
made the GPS receiver less accurate. These errors are called selective
availability, or SA. This made the position reported by a GPS receiver that
met their specification to be within 100 meters horizontally and 150 meters
vertically 95% of the time. (The position can be worse than that the other
5% of the time.) In other words, the position shown on your receiver was
within 100 meters of your actual position, 95% of the time. That’s over 300
feet!
Selective availablility was turned off in May, 2000. As of this writing, the
government has not published an accuracy specification for the GPS sys-
tem. Currently, we are seeing an accuracy of 20 meters or less. Far better
than when SA was on. However, if you do want better performance, many
manufacturers (including Eagle) sell a DGPS receiver that attaches to
your GPS receiver. The DGPS system transmits correction signals that
increase the accuracy of the GPS receiver to about 10 meters. The DGPS
receiver takes signals from these land-based transmitters and gives them
to the GPS receiver which then uses them to show a more accurate posi-
tion. (You can use the signals from all of the Coast Guard DGPS stations
for free, by the way.) The downside to this is it requires another piece of
electronic gear (the DGPS receiver) . And you have to be close enough to
a station to receive the DGPS signals.
government has not published an accuracy specification for the GPS sys-
tem. Currently, we are seeing an accuracy of 20 meters or less. Far better
than when SA was on. However, if you do want better performance, many
manufacturers (including Eagle) sell a DGPS receiver that attaches to
your GPS receiver. The DGPS system transmits correction signals that
increase the accuracy of the GPS receiver to about 10 meters. The DGPS
receiver takes signals from these land-based transmitters and gives them
to the GPS receiver which then uses them to show a more accurate posi-
tion. (You can use the signals from all of the Coast Guard DGPS stations
for free, by the way.) The downside to this is it requires another piece of
electronic gear (the DGPS receiver) . And you have to be close enough to
a station to receive the DGPS signals.
Generally, you find that using your GPS receiver without DGPS is both
easy and amazingly accurate. It’s easily the most accurate method of
electronic navigation available to the general public today. Remember,
however, that this receiver is only a tool. Always have another method of
navigation available, such as a chart or map and a compass.
easy and amazingly accurate. It’s easily the most accurate method of
electronic navigation available to the general public today. Remember,
however, that this receiver is only a tool. Always have another method of
navigation available, such as a chart or map and a compass.
Also remember that this unit will always show navigation information in
the shortest line from your present position to a waypoint, regardless of
terrain! It only calculates position, it can’t know what’s between you and
your camp, for example. It’s up to you to safely navigate around obstacles,
no matter how you’re using this product.
the shortest line from your present position to a waypoint, regardless of
terrain! It only calculates position, it can’t know what’s between you and
your camp, for example. It’s up to you to safely navigate around obstacles,
no matter how you’re using this product.