Position Modes (Kalman Filter Algorithm) - ashtech DG16 Reference Manual

longitude are computed, and the altitude is held if only three satellites are
locked. If more than three satellites are used and the HDOP is less than
the specified HDOP mask, all three polar components are computed. If
HDOP is higher than the specified HDOP mask, the DG16 automatically
goes into the altitude hold mode. The receiver stops computing positions if
the number of satellites tracked falls below three.

Position Modes (Kalman Filter Algorithm)

The DG16 can operate in one of two position modes using the Kalman Filter
Algorithm: 3D and 2D.
• Mode 0: 3D
3D mode is the standard and default mode of operation for the DG16. In 3D
mode, four locked satellites are required to compute the initial position. After
the initial fix, the DG16 can maintain operation regardless of the number of
satellites tracked. When the number of tracked satellites drops to zero, the
DG16 can maintain navigation operation depending on the Kalman filter
prediction algorithm; this is the prediction mode. You can choose whether or
not the DG16 operates in prediction mode. Position fixes obtained during the
prediction mode are flagged "predicted" in GGA and other NMEA messages
containing position information, regardless if the receiver is in stand-alone
mode or differential mode.
In the $PASHS,KFP,PRI command, you can set the maximum allowable
length of time for the DG16 to operate in Prediction Mode (Prediction
Interval). The default interval for prediction mode is 10 seconds. After the
prediction mode has timed-out, the DG16 needs at least four satellites in 3-D
mode, and 3 satellites in 2-D mode, to reset its Kalman filter and resume
positioning using the reference altitude set in the $PASHS,FIX command.
In addition, you can set the receiver to not computea position if the number of
satellites used in the solution is less than a set number using $PASHS,PMD
command.
If you have set the DG16 to Static KF mode and only 1 satellite is available,
the position is still not considered predicted because Kalman filter, in this
case, is nothing but sequential least squares. Altitude remains constant for
the entire prediction interval.
If you set PMD to 1 or 3 (adaptive 2-D mode), the Kalman filter changes from
3-D to 2-D mode if the number of satellites drops below 4., and then the
Basic Operation
DEFAULT SETTINGS
—
$PASHS,PMD Position Mode 1
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