GPGSA

GPS DOP and active satellites

Platform:

OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, SPAN CPT7, SMART7, SMART2

Firmware Stream:     

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 both systems) or GA (Galileo satellites only).

Message ID: 221

Log Type: Synch

Recommended Input:

log gpgsa ontime 1

Example 1 (GPS only):

$GPGSA,M,3,17,02,30,04,05,10,09,06,31,12,,,1.2,0.8,0.9*35

Example 2 (Combined GPS and GLONASS):

$GNGSA,M,3,17,02,30,04,05,10,09,06,31,12,,,1.2,0.8,0.9*2B

$GNGSA,M,3,87,70,,,,,,,,,,,1.2,0.8,0.9*2A

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. See Messages for more information.

 

$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

*xx

Check sum

*hh

*3F

20

[CR][LF]

Sentence terminator

 

[CR][LF]

 

OM-20000167 v13

October 2019

Email comments to NovAtel_TPUBS@NovAtel.com

7.07.03 / OM7MR0703RN0000
PP7 07.07.03 / EP7PR0703RN0000
7.06.03 / OA7CR0603RN0000