AR Validation over NMEA

Reach Module / M+ / M2 Getting started
1

Hi all,

I am using two Reach RS receivers (base and rover). The rover is connected via Bluetooth to a raspberry Pi. I can read in four NMEA message types - GPGSA, GPGSV, GPRMC and GPGGA.

I would like the AR validation ratio to be available to the Raspberry Pi so that I know when I have a valid RTK fix.

Is it possible to get this information (or similar) from the NMEA messages or do I need to use another format?

Regards, Ben

2

Lefebure ntrip read solution status from bluetooth, so the messages is there.
No sure how PI works…

3

Hi @TB_RTK,

Thanks for your reply. I’m not looking for an existing application. My question is regarding which of the available output formats I should use in my own application. The Reach RS has the following position output formats available:

  • LLH
  • XYZ
  • ENU
  • NMEA 0183
  • ERB

I’m currently using the the NMEA 0183 format. So far this format has suited my needs well.

However, I now realize that my application needs to know when the position data is considered “fixed” (AR validation ratio > 3).

Is there someway of obtaining the accuracy of the position data using the NMEA format?

I’m not familiar with any of the other formats. If I need to switch to another format which one would you recommend?

Regards, Ben

4

@BenLewis

Unfortunately there isn’t any NMEA message that is currently passed from the Reach out that has the accuracy. The GGA message includes the solution type though. This will indicate if you have a fixed solution or not.

 $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47

Where:
     GGA          Global Positioning System Fix Data
     123519       Fix taken at 12:35:19 UTC
     4807.038,N   Latitude 48 deg 07.038' N
     01131.000,E  Longitude 11 deg 31.000' E
     1            Fix quality: 0 = invalid
                               1 = GPS fix (SPS)
                               2 = DGPS fix
                               3 = PPS fix
			       4 = Real Time Kinematic
			       5 = Float RTK
                               6 = estimated (dead reckoning) (2.3 feature)
			       7 = Manual input mode
			       8 = Simulation mode
     08           Number of satellites being tracked
     0.9          Horizontal dilution of position
     545.4,M      Altitude, Meters, above mean sea level
     46.9,M       Height of geoid (mean sea level) above WGS84
                      ellipsoid
     (empty field) time in seconds since last DGPS update
     (empty field) DGPS station ID number
     *47          the checksum data, always begins with *

Because you can only achieve a fixed solution with an AR ratio of 3 or above, your NMEA message will show a solution type of 4.

1 Like
5

Hi @surveyor,

I think that is exactly what I’m looking for. I’ll give it a try. Thanks.

Regards, Ben

6

Hi Nicholas (@surveyor),

I tested your solution and it works as expected. Thanks once again.

Regards, Ben

1 Like