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NMEA-GP-GGA

Description:

Standard NMEA: Global positioning system fix data. This message contains time, date, position (in LLH coordinates), fix quality, number of satellites, and horizontal dilution of precision (HDOP) data provided by the selected source.

Configuration:

  • NMEA-GP-GGA_GNSS for combined (average) output from both receivers

    • The time and position data is the average between GNSS1 and GNSS2.

    • The fix type, number of satellites and PDOP values are from the “best” receiver.

    • The message is only valid if both receivers have a valid fix.

  • NMEA-GP-GGA_GNSS1 for output from GNSS 1 receiver

    • This is the standard NMEA GGA for GNSS1.

  • NMEA-GP-GGA_GNSS2 for output from GNSS 2 receiver

    • This is the standard NMEA GGA for GNSS2.

  • NMEA-GP-GGA_FUSION for output from Fusion

    • The time and position data is from the Fusion solution.

    • The fix type, number of satellites and PDOP values are from the “best” GNSS receiver.

    • The message is only valid if Fusion data is valid (Fusion initialized and propagation successful).

    • The quality indicator is:

      • When fusion is using GNSS: The GNSS state (RTK fixed, RTK float, SPP) of the best GNSS receiver.

      • When fusion not using GNSS: Dead-reckoning or none depending on the state of fusion.

  • NMEA-GP-GGA_GNSS1TOS for top-of-second 1Hz strict NMEA output from GNSS 1 receiver

    • Like NMEA-GP-GGA_GNSS1, but only the top-of-second message

    • Always strict NMEA (the high-precision NMEA configuration has no effect)

    • The intended use is for time sync applications that use the PPS output of GNSS1 (for example, gpsd and chrony)

    • See also NMEA-GP-RMC_GNSS1TOS

  • NMEA-GP-GGA_NTRIP for top-of-second 1Hz strict NMEA message for NTRIP

    • The time is system time (which is synced with GNSS time)

    • The position data is the last known position from GNSS1, with fallback to GNSS2, with fallback to Fusion

      • Old position information is used for up to 30 seconds

    • The fix type, number of satellits, PDOP, and quality indicators are fixed

      • No position available: quality=0, num_sv=0, pdop=99.99

      • Position available: quality=1, num_sv=10, pdop=02.00

    • Always strict NMEA (the high-precision NMEA configuration has no effect)

    • In this version diff_age and diff_sta fields are always null

    • Do not use this position for any other purpose than sending it to a NTRIP caster to get a VRS

Notes:

  • These messages does not contain any information that would let one tell them apart. Do not enable more than one of these in the same port.

  • This message is according to NMEA 0183 v4.11 (and erratas).

  • It uses the “GP” talker ID even though the navigation solution is multi-GNSS.

Example message:

CODE
$GPGGA,090924.00,4724.01791,N,00827.02194,E,4,12,99.99,459.4,M,,,0.3,0000*16*3A\r\n

Example message with non-standard high-precision fields:

CODE
$GPGGA,090411.2001,4724.0179046,N,00827.0219436,E,4,30,99.99,459.4117,M,,,0.4,0000*28\r\n

Message fields:

#

Field

Format

Unit

Nullable

Example

Description

1

time

hhmmss.ss(ss)

-

Y

151229.40

UTC time (hours, minutes and seconds)

2

lat

ddmm.mmmmm(mm)

-

Y

4723.54108

Latitude

3

lat_ns

Character

-

Y

N

Latitude north (N) or south (S) indicator

4

lon

dddmm.mmmmm(mm)

-

Y

00826.88485

Longitude

5

lon_ew

Character

-

Y

E

Longitude east (E) or west (W) indicator

6

quality

Digit

-

N

4

Quality indicator, 4 (RTK fixed), 5 (RTK float), 1 (non-RTK fix), 6 (dead-reckoning), 0 (invalid)

7

num_sv

Decimal

-

N

12

Number of satellites. Range 00-12 in strict NMEA mode, 00-99 in high-precision NMEA mode

8

hdop

Float (.2)

-

N

0.98

Horizontal dilution of precision, range 0.10-99.99

9

alt

Float (.1/.4)

m

Y

473.5

Altitude (above ellipsoid)

10

alt_unit

Character

-

Y

M

Altitude unit, always M (metres)

11

sep

-

-

Y

Geoid separation, always null

12

sep_unit

-

-

Y

Geoid separation unit, alwyas null

13

diff_age

Float (.1)

s

Y

1.5

Approximate age of differential data (last GPS MSM message received)

14

diff_sta

-

-

Y

0000

DGPS station ID (0000-1023)

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