Reference Information
LD8 Operations Manual
AB- V-MA-00635_RevA6
34
5.3.4 GSA Sentence
The NMEA GSA sentence contains the GNSS receiver operating mode, active satellites used in the navigation
solution, and DOP values.
GSA Sentence Structure & Example
$GNGSA, a, 1, cc, cc, cc, cc, cc, cc, cc, cc, cc, cc, cc, cc, d.d, e.e, f .f *hh
$GNGSA, a, b, 02, 12, 15, 20, 21, 24, 25, 29, 32, , , , 1.7, 0.9, 1.5 *58
GSA Sentence Defined
Field
Content
GSA
GNSS DOP and Active Satellites
a
Mode (M = Manual mode, forced to operate in 2D or 3D mode,
A = Automatic mode, allowed to automatically switch 2D/3D)
b
Fix (1 = Not available, 2 = 2D, 3 = 3D)
cc
PRN ID numbers of satellites used in solution a total of 12 fields
GPS = 1 to 32
GLONASS = 65 to 96
As shown in the above example, if less than 12 satellites for one constellation are used null
values will be output in the string.
d.d
PDOP
e.e
HDOP
f.f
VDOP
hh
Checksum
5.3.5 VTG Sentence
The NMEA VTG sentence provides the actual course and speed relative to the ground.
VTG Sentence Structure & Example
$GNVTG, ppp.ppp, T, qqq.qgg, M, rr.rrr, N, ss.sss, K, U, *hh
$GNVTG, 167.608, T, 167.608, M, 0.006, N, 0.012, K, D, *3D
VTG Sentence Defined
Field
Content
VTG
Course over ground and ground speed
ppp.ppp True course over ground
T
Degrees True indicator
qqq.qgg Magnetic course over ground
M
Degrees Magnetic
rr.rrr
Speed over ground, knots
N
Nautical speed indicatior (N = Knots)
ss.sss
Speed over ground, kilometres/hour
K
Speed indicator (K = km/hr)
U
Positioning mode indicator (A = Autonomous, D = Differential,
E = Estimated (Dead reckoning), M = Manual, N = Data not valid)
*hh
Checksum
