Ultimate GPS Logger Shield – Confusion about correct fix

[sp100]

Hello!
I am working with GPS and the shield for the first time. Attached is a screenshot of some data that was parsed using the "Adafruit_GPS" library and the appropriate example code.

– Can somebody explain to me, why the quality changed from 0 to 2 indicating a change from invalid to DGPS, when I cannot see an obvious change in the sentence itself?
– Does it have to do with the checksum at the end or something?
– Is the data really invalid? Why, since nothing really changed?
– Can the module use DGPS? Where does the reference come from?

This change occurred approx. 10 mins after the fix.

Thanks in advance.

[adafruit_support_mike]

You seem to be comparing the $GPGGA sentences to the $GPRMC sentences. That doesn't work. The fields have different meanings.

The value after 'E' in the $GPRMC sentence is actually 0.02, which is ground speed in knots.

This page has a breakdown of NMEA sentences and what they mean:

http://www.gpsinformation.org/dale/nmea.htm

[sp100]

Thanks for the fast reply. I am very sorry for making this not clear enough. I was referring to the GGA sentence where after time, latitude, longitude comes fix and then number of satellites. Which in my attachment is fix = 2 and satellites = 9 all the time.

In the RMC sentence is A for active all the time also. So I want to understand, where the change in the parsed information comes from? And how DGPS is possible?

Does this make more sense now?

[adafruit_support_mike]

The code that parses the NMEA sentences is in the Adafruit_GPS library: https://github.com/adafruit/Adafruit-GP ... it_GPS.cpp

In this case, the fix quality is read from the $GPGGA sentence. The parsed output follows the NMEA sentence itself though, so the one that gave you the 'quality: 0' output would be the one above the text that you posted.

The GPS modules are capable of doing DGPS and SBAS. The commands to enable/disable them are:

Code: Select all

set DGPS mode:          $PMTK301,1*2D
disable DGPS mode:      $PMTK301,0*2C

set SBAS mode:          $PMTK319,1*24
enable SBAS:            $PMTK313,1*2E
disable SBAS:           $PMTK313,0*2F

and are explained in the GPS module's command datasheet:

http://www.adafruit.com/datasheets/PMTK ... 39-A01.pdf