gps-wizard

GGA - GNSS Fix

Summary

This is one of the sentences always supported by GPS / GNSS receivers.

The GGA sentence includes time, position and fix related data for a GPS / GNSS receiver.

Notes about the number of satellites in use:

• The maximum number of SVs (satellites) reported by GGA may be limited to 12.
• The GNS sentence (if available) will correctly report the actual number of satellites in use.

Structure

                                                      11
        1         2       3 4        5 6 7  8   9  10 |  12 13  14   15
        |         |       | |        | | |  |   |   | |   | |   |    |
 $--GGA,hhmmss.ss,ddmm.mm,a,ddmm.mm,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh<CR><LF>

#	Field	Format	Example	Description
0	Sentence ID	string	$GPGGA	Talker ID (GP) + message ID (GGA)
1	Time	hhmmss.sss	092751.000	UTC time, typically 2 or 3 dp. Leading zeros are always included
2	Latitude	ddmm.mmmm	5321.6802	Latitude, typically 4 or 5 dp. Leading zeros are always included
3	NS	character	N	Hemispherical orientation N or S (north or south)
4	Longitude	dddmm.mmmm	00630.3371	Longitude, typically 4 or 5 dp. Leading zeros are always included
5	EW	character	W	Hemispherical orientation E or W (east or west)
6	Quality	digit	1	Quality indicator
7	Num SV	numeric	12	Number of space vehicles (satellites) in use (00-12)
8	HDOP	numeric	3.2	Horizontal dilution of precision (HDOP), typically 1 or 2 dp
9	Elevation	numeric	3.04	Antenna altitude above/below mean-sea-level, typically 1 or 2 dp
10	Elevation unit	character	M	Fixed field. M = meters
11	Separation	numeric	48.8	Geoidal separation in meters, difference between ellipsoid and mean-sea-level
12	Separation unit	character	M	Fixed field. M = meters
13	DGPS age	numeric	-	Age of differential corrections in seconds (null when DGPS is not used)
14	DGPS station	numeric	0000	Differential reference station ID; 0000-1023. Null (empty) or 0000 when DGPS not used
15	Checksum	hexadecimal	*7B	Checksum

Notes:

• The sentence ID will be $GPGGA or $GNGGA.
• Jackson Labs replace the quality indicator with GPSDO status.
• Some chipsets will limit the number of satellites to 12, so check for GNS which does not have the limit.
• Ellipsoid altitude = MSL altitude + Geoid separation, according to SiRF documentation.
• The DGPS age and station (fields 13 + 14) are absent in the example from “NMEA Revealed”.

Examples

NMEA Revealed

$GNGGA,001043.00,4404.14036,N,12118.85961,W,1,12,0.98,1113.0,M,-21.3,M*47

Wikipedia

$GPGGA,092750.000,5321.6802,N,00630.3372,W,1,8,1.03,61.7,M,55.2,M,,*76
$GPGGA,092751.000,5321.6802,N,00630.3371,W,1,8,1.03,61.7,M,55.3,M,,*75

Locosys GT-31

$GPGGA,125901.000,5637.8345,N,01638.4927,W,1,04,3.2,3.04,M,48.8,M,,0000*7B

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