ComNav Commander P2 - Table 12 - NMEA Sentence Priority

ComNav Commander P2 & P2VS Installation & Operation Appendices
Document PN 29010074 V4.1 - 187 -
Sentence
Priority
(higher to lower)
Sentence Data Used
11 *XTE Cross-Track Error
12 *BOD
Bearing Origin to Destination Magnetic & True,



Waypoint ID
13 *VBW
Boat Speed



14 *VHW
Boat Speed



15 *VTG
Boat Speed



16 *BWC
Bearing Present to Destination Magnetic & True,



Distance to Waypoint Nautical Miles,
Waypoint ID
(Bearing & Distance are on a Great Circle)
17 *HDG Magnetic Heading,
Magnetic Variation



18 *HDT True Heading
19 *HDM Magnetic Heading
Table 12 - NMEA Sentence Priority



The different units of Wind Speed (Knots, m/s & Km/H) present in these
sentences are all used in Wind calculations by the autopilot.



Magnetic Variation (for setting a Course, but not for Heading) is calculated from
the True & Magnetic values in these sentences.



The units of Boat Speed (Knots & Km/H) are present in these sentences, but do
not matter to the autopilot, since all displays & functions related to Boat Speed
are used without units.
If both Knots & Km/H values are present in the sentence (in the case of VTG, VHW,
VBW only, since the speed values in RMA & RMC are always in Knots), the Knots
value is used.
If the VBW sentence is being used, the Longitudinal Water Speed value (in Knots)
from it is used for Boat Speed.
The Speed values in RMA, RMC & VTG are Speed Over Ground; the others are
relative to the water.



Magnetic Variation from this sentence is used only for Heading, not for Course.
Note: the VWR, VWT, APA & HDM sentences are classified as “not recommended
for new designs” in NMEA 0183 Version 3.00. However, they have been
included in the P Series “accepted” list to allow use with existing equipment that
might still use them.