SHOUT 3G User Guide Version B
Document Number: 451-93218-002B
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Figure 25:
Reset Ephemeris
Key
Monitor the accuracy of the position by observing the Horizontal Accuracy (HACC). HACC is
measured in meters. HACC is defined as the radius of a circle centered on the true value that
contains the GPS measurement. Thus, a position fix with ten meters’ HACC accuracy indicates
that it is within ten meters of the true position—the higher the HACC value, the less accurate
the GPS measurement.
The Chk GPS option is a good indicator of whether or not the GPS receiver has sufficient signal
to initiate a Waypoint or a Test Report when located in a challenging environment, e.g., in
dense foliage or around urban settings with tall buildings. You can monitor HACC in real-time to
ensure it converges to a small and stable value (usually less than 30 meters). At which point, it
is certain that a 3D fix can be obtained with the most current ephemeris data being updated
and saved. You can then go back to the
Utilities
menu to send a test report. When the GPS
receiver cannot acquire a fix, HACC gradually increases and at some point stops at a value of
4294967.500. It is an indication that the surrounding obstructions prevent the GPS receiver
from obtaining a fix and you should move on to a different location.
