74
94-0561-D
Marine Technologies (Custom)
The MT Custom DP String adopts NMEA0183 conventions with a minimum length of 63 and maximum length of 80 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).
$PGNMT,T,HH˽MM˽SS.SSS,[NNNN]N,E,[IIII]I,S,[RRR]R.RR,
Z
R
.Z
R
Z
R
,[BB]B.BB,
Z
B
.Z
B
Z
B
,[Q]Q,[AAA]A,XXXX*CC<CR><LF>
Where:
$PGNMT
Proprietary header
6 chars
T
Type field for SceneScan [S]
1 char
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
E
Sequence identifier
1 char
[IIII]I
Scene Reference Point ID
1 char
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
[AAA]A
†
Age of measurement in ms
1–4 chars
XXXX
Reserved – 16 bit flags in hex
4 chars
*
Delimiter
1 char
CC
Checksum
2 chars
<CR><LF>
Carriage return and Line Feed
2 chars
10.8
Configuring the SceneScan System
10
DP Message Types (continued)
†
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.