Furuno VR-3000 Operator's Manual page 42

GNS - GNSS fix data
Fix data for single or combined satellite navigation systems (GNSS).
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$--GNS,hhmmss.ss,llll.lll,a,yyyyy.yyy,a,c--c,xx,x.x,x.x,x.x,x.x,x.x,a*hh<CR><LF>
1) UTC of position
2) Latitude, N/S
3) Longitude, E/W
4) Mode indicator
Mode indicator. A variable length valid character field type with the first three characters currently defined.
The first character indicates the use of GPS satellites, the second character indicates the use of GLONASS
satellites and the third indicate the use of Galileo satellites. If another satellite system is added to the
standard, the mode indicator will be extended to four characters, new satellite systems should always be
added on the right, so the order of characters in the mode indicator is: GPS, GLONASS, Galileo, other
satellite systems in the future. The characters should take one of the following values.
A = Autonomous. Satellite system used in non-differential mode in position fix.
D = Differential. Satellite system used in differential mode in position fix
E = Estimated (dead reckoning) mode
F = Float RTK. Satellite system used in real time kinematic mode with floating integers
M = Manual input mode
N = No fix. Satellite system not used in position fix, or fix not valid
P = Precise. Satellite system used in precision mode. Precision mode is defined as: no deliberate
degradation (such as selective availability) and higher resolution code (P-code) is used to compute
position fix. P is also used for satellite system used in multi-frequency, SBAS or Precise Point
Positioning (PPP) mode.
R = Real Time Kinematic. Satellite system used in RTK mode with fixed integers
S = Simulator mode
5) Total number of satllite in use,00-99
6) HDOP
HDOP calculated using all the satellites (GPS, GLONASS, Galileo and any future satellites) used in
computing the solution reported in each GNS sentence.
7) Antenna altitude, m, re: mean-sea-level(geoid)
8) Geoidal separation
Geodial Separation: the difference between the earth ellipsoid surface and mean-sea-level (geoid) surface
defined by the reference datum used in the position solution, "-" = mean-sea-level surface below ellipsoid.
The reference datum may be specified in the DTM sentence.
9) Age of differential data (see Note.)
10) Differential reference station ID (see Note.)
11) Navigation status indicator
The navigational status indicator is according to IEC 61108 requirements on 'Navigational (or Failure)
warnings and status indications'. This field shoule not be a NULL field and the character should take one
of the following values:
S = Safe
C = Caution
U = Unsafe
V = Navigational status not valid, equipment is not providing navigational status indication.
Note
Age of differential data and Differential Reference Station ID:
:
a) When the talker is GN and more than one of the satellite systems are used in
differential mode, then the "Age of differential data" and "Differential reference station ID"
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When the estimated positoning accuracy (95 % confidence) is within the selected
accuracy level corresponding to the actual navigation mode, and integrity is available
and within the requirements for the actual navigation mode, and a new valid position
has been calculated within 1 s for a conventional craft and 0.5 s for a high spee craft.
When integrity is not available
When the estimated positioning accuracy (95 % confidence) is less than the selected
accuracy level corresponding to the actual navigation mode, and/or integrity is available
but exceeds the requirements for the actual navigation mode, and/or a new valid
position has not been calculated within 1 s for a conventional craft and 0.5 s for a high
speed craft.
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