l
74
DP Message Types (Continued)
Rolls-Royce Custom DP String
The Rolls-Royce Custom DP String adopts NMEA0183 conventions with a minimum length of of 82 characters. Two messages are emitted per rotor revolution, one for the Scene Reference
Point and one for a secondary virtual reference point (that is at a fixed offset from the Scene Reference Point).
$PGNRR,T,YYYY MM DD,HH MM SS.SSS,…N,…I,S,…R.RR,Z
R
.Z
R
Z
R
,…B.BB,Z
B
.Z
B
Z
B
,…Q,±…r.r,±…p.p,…A,XXXX*CC<CR><LF>
Where:
•
$PGNRR
Proprietary header
6 chars
•
T
Type field for SceneScan [S]
1 char
•
YYYY MM DD
Real-time clock date at message transmission to DP [1-9]
10 chars
•
HH MM SS.SSS
Real-time clock time at message transmission to DP
12 chars
•
[NNNN]N
16-bit revolution counter in decimal
1–5 chars
•
[IIII]I
Scene Reference Point ID
1–5 chars
•
S
Status [V]oid or [N]avigating
1 char
•
[RRR]R.RR
Range in metres
4–7 chars
•
Z
R
.Z
R
Z
R
Range standard deviation in metres
4 chars
•
[BB]B.BB
Bearing in degrees (clockwise from bow)
4–6 chars
•
Z
B
.Z
B
Z
B
Bearing standard deviation in degrees
4 chars
•
[Q]Q
Scene Similarity [%]
1–2 chars
•
±[r]r.r
Sensor roll in degrees at time of last valid position measurement
4–5 chars
•
±[p]p.p
Sensor pitch in degrees at time of last valid position measurement
4–5 chars
•
[AAA]A
†
Age of measurement in ms at transmission time
1–4 chars
•
XXXX
Reserved – 16 bit flags in hex
4 chars
•
*
Delimiter
1 chars
•
CC
Checksum
2 chars
•
<CR><LF>
Carriage return and Line Feed
2 chars
†
The ‘age’ is the accumulated time in milliseconds from the
moment the measurement was made until the moment the
message string is constructed, prior to being transmitted to the
DP system. It effectively gauges the lag through the system,
which may not be constant. Having a value for the lag allows
for subsequent correction of the measurement.
Summary of Contents for 20-0253
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