ashtech GG Surveyor, Reference Manual

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64 GG Surveyor GPS+GLONASS Reference Manual
GST estimates of latitude, longitude, and altitude accuracy automatically account for
DOP, SNR, and many other factors. These parameters are built into the GST estimate
already and do not have to be recomputed by the user.
Required Number of Satellites
The receiver requires seven or more satellites to fix integers, following power on, or
obstruction and re-acquisition. If the solution is fixed with 7 or more satellites, and
the number of satellites falls below 7 but stays above 3, the solution stays fixed and
accuracy remains at the centimeter-level. If the solution is not fixed, but the receiver
has four, five, or six satellites in view, the solution will be floating-point, and steadily
converges to sub-decimeter accuracy. Positions are always three-dimensional when in
RTK mode. Two-dimensional positions, using previously calculated altitudes, are not
possible.
Mask Angles
At the remote station the position elevation mask is always controlled by
$PASHS,PEM, whether the receiver is in Differential mode or RTK mode.
Figure 5.4: Typical GST Performance
0.001
0.01
0.1
1
1 25 49 73 97 121 145 169 193 217 241 265 289 313 337 361 385 409 433 457 481
Seconds
Horizon
tal error (m)
GST 2-sigma
GST 1-sigma
Actual Error
“Float” Solution
“Fixed” Solution