Before a coordinate ever lands in your field software, your GNSS receiver has already done something most surveyors never think about: it translated raw satellite signals into a stream of structured text, formatted it according to a protocol developed by a marine electronics association in the 1980s, and fired it down a wire or wireless connection to whatever device is listening. That protocol is NMEA 0183, and it is the invisible backbone of nearly every piece of positioning equipment in use today, from the Hemisphere S631 on your survey pole to the machine control systems grading a highway.
Where NMEA Came From
How NMEA Data Is Structured
The Sentence Types That Matter in Surveying
Fix Quality: What the Numbers Mean
Why NMEA Compatibility Matters When Choosing Equipment
From the Receiver to Your Software
NMEA Is the Language Your Equipment Already Speaks
The National Marine Electronics Association created the NMEA 0183 standard originally to solve a simple problem: boat instruments couldn’t talk to each other. Depth sounders, compasses, and chart plotters all spoke different languages. NMEA gave them a common one.
When civilian GPS expanded in the late 1980s and into the 1990s, manufacturers adopted NMEA 0183 because it was already there, already lightweight, and already understood by the hardware ecosystems of the time. By the time surveying, agriculture, construction, and aviation started relying on GNSS, NMEA was simply part of the package. Today it remains the dominant output format for survey-grade GNSS receivers, and understanding it makes you a smarter operator regardless of what brand you’re running.
NMEA works by transmitting individual lines of data called sentences. Each sentence is a plain-text string that begins with a dollar sign and ends with a checksum. The format looks like noise at first glance, but every character has a defined role.
The first part of the sentence identifies the talker, the device or constellation type sending the data. You’ll commonly see:
For any modern receiver operating in North America, GN is the talker ID you want. It means your equipment is pulling from every available constellation, which matters when you’re working near tree lines, buildings, or in terrain that cuts off parts of the sky.
Not all NMEA sentences are created equal. Some contain position data; others describe the satellite geometry or signal quality. For day-to-day survey work, a handful of sentence types carry the most weight:
When Bench-Mark sets up a receiver for a client integrating GNSS into a third-party platform, whether that’s a GIS app, a data collector, or construction control hardware, GGA is almost always the required sentence. If the downstream device also needs velocity or heading, RMC gets added to the stream.
Inside the GGA sentence is a single-digit fix quality indicator that tells you exactly what kind of position your receiver has at any moment. It’s easy to miss, but it’s one of the most important values in the data stream.
A value of 0 means no fix, the receiver has no usable position. A value of 1 indicates a standard GPS or GNSS fix, which is meter-level or worse depending on conditions. A value of 2 means DGPS, which is sub-meter. A value of 4 is the one you want for professional survey work: RTK fixed. That’s your centimeter-level solution. A value of 5 is RTK float, which is better than DGPS but hasn’t fully converged, you’re somewhere in the low-decimeter range and shouldn’t be collecting final survey data.
Knowing this number means you never have to guess whether you were on a fixed solution when you collected a point. It’s in every single GGA sentence your receiver outputs.
One of the advantages of the open GNSS ecosystem, the one Bench-Mark operates in, is that NMEA compatibility is genuinely universal. The Hemisphere S631, the GeoMeasure Nano 7, and the GeoMax Zoom95 all output standard NMEA 0183. That means they can integrate with FieldGenius, with ArcGIS Field Maps, with AutoCAD, and with a wide range of construction and engineering platforms without proprietary adapters or locked workflows.
Contrast that with some of the closed ecosystems in the industry where the hardware, software, and data formats are all controlled by a single manufacturer. When everything is proprietary, NMEA output may be restricted or require additional licensing to access. For surveyors who need to feed data to multiple platforms or legacy systems, that creates real friction in the field.
NMEA 0183 transmits at a standard baud rate of 4800 for legacy setups, though modern receivers often support higher rates. Output frequency is typically set at 1 Hz, one position update per second, which is appropriate for most static and RTK survey workflows. For machine control or dynamic positioning applications, you may push that to 5 or 10 Hz, but confirm the downstream device can handle the increased data rate before doing so.
The physical path NMEA data takes depends on how your system is configured. Common interfaces include:
The interface changes, but the NMEA sentences are identical regardless of how they’re traveling. That consistency is exactly why the standard has lasted for decades without being replaced.
NMEA is the live voice of your receiver, broadcasting position, quality, and satellite data every second you’re in the field. When your fix drops, when your software flags a bad point, when your machine control system loses its position reference, NMEA sentences are where you find the answer. Surveyors who understand the structure of that data stream can diagnose problems faster, configure integrations correctly, and make smarter decisions about when to trust a position and when to wait. At Bench-Mark, we build our support around exactly that kind of knowledge, because the equipment is only as useful as your understanding of what it’s telling you.
