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|  MIL-D-70789A (AR)
3.10.6.2 Position update. After the DRU has entered the
Survey mode, it shall compare any position coordinates entered
via the serial data buses to the present internal estimate of DRU
position. If the position differences are within the following
tolerance:
3 (DRU Estimated Error) +X meters, the DRU shall
accept them and complete the update. If the difference for any
one of the updated parameters exceeds the tolerance, the entire
update shall be rejected and an alert indicated in the STATUS
word. ALERT DATA Character D4, bit 0, shall be set for excessive
horizontal position error if the difference exceeds 3 (DRU
Estimated Error) +X meters but does not exceed 12 (DRU Estimated
Error) +Y meters. ALERT DATA Character D4, bit 1, shall be set
for excessive Altitude error if the difference exceeds 3 (DRU
Estimated Error) +X meters but does not exceed 12 (DRU Estimated
Error) +Y meters. ALERT DATA Character D4, bit 3, shall be set if
the difference for horizontal position exceeds 12 (DRU Estimated
Error) +Y meters. ALERT DATA Character D4, bit 4, shall be set if
the difference for Altitude exceeds 12 (DRU Estimated Error) +Y
meters. (When an entire update has been rejected, the operator
will check whether an error was made in the keyboard entry or
whether the vehicle is at the correct survey control point. He
will exercise judgment to determine whether the update should be
abandoned or whether he should follow procedures that will make
the DRU accept the update An spite of the alert(s). In the
extreme case, if ALERT DATA Character D4, bit 3 and 4 were set,
the DRU shall accept an update if the data is reentered after
RESTART is commanded). When an update has been rejected, the
data shall be stored for comparison purposes in case the data is
reentered. If the reentered data is not the same, or if the
reentered data is "the same but the vehicle has been moved, the
data shall be tested against the normal tolerance and either
accepted or appropriate alert(s) set, i.e., the same as if the
data were being entered for the first time. If the reentered data
is the same and the vehicle has not been moved, the update shall
be accepted if D4/3 and/or D4/4 were not previously set.
Otherwise, the update shall be rejected and the same alert(s)
set. If either D4/3 alert or D4/4 alert is inhibiting an update,
the operator may accomplish a partial update by proper choice of
update groupings (3.5.7). For example, if an update of grouping
b.
(3.5.7) was attempted and rejected because D4/4 was set, the
operator may choose grouping c. and accomplish an update. If
D4/0 were also set, the update would be accepted with only one
reentry of data, assuming all other criteria for update were met.
The X and Y tolerance values are:
Coordinate
X(m)
Y (m)
Horizontal
Position
10
150
Altitude
5
50
87
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