First defined by the National Marine Electronics Association, NMEA is currently the most common data format supported by GNSS equipment. It allows connecting different types of hardware and software. Reach receivers use NMEA format to send the position data to third-party GIS apps and diverse machinery: from tractors to drones and robots.
Though, various applications require different types of NMEA messages. This article will try to figure out the main types of NMEA messages and how you can use them for your projects with Reach devices.
NMEA Standard in Geopositioning
The NMEA messages consist of so-called “sentences” with GNSS data transmitted from a “talker” device to a “listener” device (or multiple devices). The standard NMEA message with position data is called GGA and contains several fields, including 3D coordinates, solution status, the number of satellites used, and other data.
NMEA messages also include a “talker ID”, a two-character prefix that identifies the type of the transmitting unit. For example, the GP talker ID means that data for the GPS constellation is transmitted. In contrast, GN means the receiver outputs data for all GNSS constellations it uses during the survey.
Besides the GGA message, there are alternative and companion NMEA messages that provide additional information. It means that various receivers can send NMEA messages with different capabilities.
For example, these types of NMEA messages contain additional GNSS data:
- GSA – GPS DOP (dilution of precision) and active satellites
- GST – position error statistics
- GSV – number of satellites in view, satellite PRN (pseudo-random noise) number, elevation, azimuth, and signal-to-noise ratio
- RMC – position, velocity, and time
- VTG – Actual track made good and speed over ground
- ZDA – UTC day, month, and year, and local time zone offset
NMEA Sentences in Reach Panel
To stream real-time position from Reach receivers to third-party devices and GIS apps, you should enable the NMEA messages in Reach Panel. Simply connect your device to Reach over Bluetooth, USB cable, or bottom connector and turn on Position output on the Position streaming screen in Reach Panel. To set up the format, choose NMEA from the drop-down list.
Setting up NMEA position output in Reach Panel
Then you can configure NMEA position streaming to use Reach with software and hardware requiring a specific NMEA output. You can set up a talker ID and the particular type of NMEA messages you need.
For Talker ID, you can choose GP or GN values. GP stands for GPS satellites only and is mostly used for integration with legacy devices and software. GN value stands for GNSS positioning and is the latest industry standard; it’s required when you use the data from multiple satellite systems.
You can also select a particular set of NMEA messages, including GGA, GSA, GST, GSV, RMC, VTG, ZDA. Before configuring NMEA position output, check the required NMEA message type in your GIS app or equipment specifications.
When setting up NMEA messages, you may also determine the output frequency rate, though the standard 1 Hz should work for most applications. If you change the NMEA output rate, note that it should be equal to or lower than the RTK Settings rate.
Specifying NMEA output parameters allows you to connect Reach rovers to agricultural equipment, GPR, and various apps: ESRI ArcGIS Collector, QField, Microsurvey FiledGenius, Autocad360, MachineryGuide, AgriBus-Navi, Efarmer, Agripilot, Mobile Topographer Pro, PointMan, Mapit GIS, LandStar.