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APPENDIX A
A
-7
HDM- Heading – magnetic
This sentence is not used in the current version of NMEA and IEC 61162. Some boaters may want the
GPS compass to indicate the magnetic heading when the boat is only fitted with a magnetic compass.
HDG is calculated by adding a geomagnetic variation to HDT.
$--HDM, x.x, M *hh<CR><LF>
Heading, degrees true
HDT - Heading - true
True heading in degrees obtained by processing RF cycle in the GPS carrier frequency.
$--HDT, x.x, T*hh<CR><LF>
Heading, degrees true
ROT – Rate of turn
ROT derived from a changing rate of GPS compass heading.
$--ROT, x.x, A*hh<CR><LF>
Status: A = data valid
Rate of turn, degrees/min, “-” = bow turns to port
VBW - Dual ground/water speed
$--VBW,x.x,x.x,A,x.x,x.x,A,x.x,A,x.x,A*hh<CR><LF>
| | | | | | | | | | |
| | | | | | | | | | +--- 11
| | | | | | | | | +----- 10
| | | | | | | | +-------- 9
| | | | | | | +----------- 8
| | | | | | +-------------- 7
| | | | | +----------------- 6
| | | | +-------------------- 5
| | | +------------------------ 4
| | +--------------------------- 3
| +------------------------------ 2
+---------------------------------- 1
1. Longitudial water speed, knots
2. Transverse water speed, knots
3. Status: water speed, A=data valid V=data invalid
4. Longitudial ground speed, knots
5. Transverse ground speed, knots
6. Status: ground speed, A=data valid V=data invalid
7. Stern transverse water speed, knots
8. Status: stern water speed, A=data valid V=data invalid
9. Stern transverse ground speed, knots
10. Status: stern ground speed, A=data valid V=data invalid
11. Checksum