GPGSA
GPS DOP and active satellites
|
Platform: |
OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, CPT7, CPT7700, SMART7, SMART2 |
This log contains GNSS receiver operating mode, satellites used for navigation and DOP values.
The GPGSA log outputs these messages without waiting for a valid almanac. Instead, it uses a UTC time, calculated with default parameters. In this case, the UTC time status (see the TIME log) is set to WARNING since it may not be one hundred percent accurate. When a valid almanac is available, the receiver uses the real parameters. Then the UTC time status is set to VALID.
If the NMEATALKER command is set to AUTO, the talker (the first 2 characters after the $ sign in the log header) is set to GP (GPS satellites only), GL (GLONASS satellites only), or GN (satellites from multiple systems) or GA (Galileo satellites only).
When the solution type is INS (SPAN models), the DOPs in the GPGGA log are calculated at a 1 Hz rate.
To determine if the receiver is providing an INS solution, check the pos type field in the BESTPOS log.
Message ID: 221
Log Type: Synch
Recommended Input:
log gpgsa ontime 1
Example 1 (GPS only):
$GPGSA,M,3,05,02,31,06,19,29,20,12,24,25,,,0.9,0.5,0.7*35
Example 2 (Multi-constellation):
$GNGSA,M,3,03,14,17,06,12,19,02,01,24,32,,,0.8,0.5,0.6*22
$GNGSA,M,3,66,85,75,67,73,84,83,,,,,,0.8,0.5,0.6*26
$GNGSA,M,3,12,11,33,31,03,24,25,08,,,,,0.8,0.5,0.6*20
$GNGSA,M,3,28,46,36,27,39,23,43,37,,,,,0.8,0.5,0.6*2B
The DOPs provide a simple characterization of the user satellite geometry. DOP is related to the volume formed by the intersection points of the user satellite vectors, with the unit sphere centered on the user. Larger volumes give smaller DOPs. Lower DOP values generally represent better position accuracy. The role of DOP in GNSS positioning is often misunderstood. A lower DOP value does not automatically mean a low position error. The quality of a GNSS derived position estimate depends upon both the measurement geometry as represented by DOP values and range errors caused by signal strength, ionospheric effects, multipath and so on.
See the Note in the GPGGA log that applies to all NMEA logs.
|
Field |
Structure |
Description |
Symbol |
Example |
|
1 |
$GPGSA |
Log header |
|
$GPGSA |
|
2 |
mode MA |
A = Automatic 2D/3D M = Manual, forced to operate in 2D or 3D |
M |
M |
|
3 |
mode 123 |
Mode: 1 = Fix not available; 2 = 2D; 3 = 3D |
x |
3 |
|
4 - 15 |
prn |
PRN numbers of satellites used in solution (null for unused fields), total of 12 fields GPS = 1 to 32 SBAS = 33 to 64 (add 87 for PRN number) GLO = 65 to 96 1 |
xx,xx,..... |
18,03,13, 25,16, 24,12, 20,,,, |
|
16 |
pdop |
Position dilution of precision |
x.x |
1.5 |
|
17 |
hdop |
Horizontal dilution of precision |
x.x |
0.9 |
|
18 |
vdop |
Vertical dilution of precision |
x.x |
1.2 |
|
19 |
system ID |
GNSS system ID. See Table: System and Signal IDs. This field is only output if the NMEAVERSION is 4.11 (see the NMEAVERSION command). |
|
|
|
20 |
*xx |
Check sum |
*hh |
*3F |
|
21 |
[CR][LF] |
Sentence terminator |
|
[CR][LF] |