GNSS Survey Errors in Nigeria: Can a FIX Solution Still Be Wrong?

For surveyors working across Nigeria, GNSS survey errors can sometimes be difficult to spot, especially when the field controller is displaying green checkmarks and a reassuring FIXED status. Horizontal RMS reads 0.008 m, Vertical RMS reads 0.012 m. Everything on the screen appears to be telling you that the RTK solution is solid. Yet when the CAD drafting is complete, or the construction team stakes out the site, the boundary point is not where it should be, or a construction point does not agree with the expected position.

Then comes the question:

“But the receiver was FIXED, and the HRMS and VRMS read perfectly. So how did the survey go wrong?”

This is where surveyors need to look beyond the word FIX and understand the difference between a fixed GNSS solution and a verified survey result.

FIX Does Not Mean “Everything Is Correct”

A FIX solution means the GNSS receiver has achieved a fixed RTK solution. But FIX does not guarantee that the coordinate you are about to store is correct.

The receiver can be FIXED while something else in your surveying workflow is wrong.

Four Common Pitfalls Behind "FIXED" Survey Errors

1. You Could Be Using the Wrong Coordinate System: Your receiver may show FIX and give you precise-looking coordinates, but are those coordinates referenced to the correct coordinate system and datum for the job?

This becomes particularly important when tying new GNSS observations to existing survey plans in places such as Lagos, Ogun, Oyo, Rivers, and Enugu, where surveyors may encounter data from different coordinate systems, datums, or survey periods.

A coordinate can be precise but still be in the wrong reference framework.

This is why surveyors need to verify their project settings before collecting points, especially when working with existing survey plans, control points, or data from different sources.

2. What About the Correction Source? RTK positioning depends on corrections from a base station, CORS network, or another correction source.

For example, a surveyor working in Lagos, Abuja, or Ebonyi may have access to different CORS services depending on the network being used and the coverage available for the project.

What matters is not simply having a correction source, but understanding the reference station or network providing those corrections.

If you are connected to the wrong reference station, using unsuitable correction settings, or the correction data is flawed, the receiver may still show a solution that looks acceptable to the operator.

Also, if you are doing a base-and-rover setup and the base is not properly set up or is using the wrong coordinates, your rover positions can also be wrong.

So, don't just look at the solution status.

Know where your corrections are coming from and whether that correction source is appropriate for the job.

3. Your Antenna Height Could Be Wrong: This is one of the simplest mistakes that can affect your results. You may have a perfectly good FIX solution, but if you entered the wrong antenna height or measured it incorrectly, the coordinate you record can still be wrong, particularly the elevation.

The receiver is doing what it was designed to do. The problem is the information the surveyor entered.

FIX cannot correct a wrong antenna height.

4. The Environment Can Still Affect Your Observation: Buildings, trees, and other objects around the antenna can affect GNSS through signal blockage, reflection, and multipath. You may eventually obtain FIX, but that does not mean the observation environment was ideal.

This is particularly important on built-up construction sites in places like Lagos and Abuja, where buildings and other structures can obstruct or reflect satellite signals.

This Is Why Checkpoints Matter

One of the simplest ways to catch a GNSS mistake is to check your work independently. If you are surveying a known control point, occupy it and compare your result with the known coordinates.

For important points, you can also re-occupy the point or observe it independently rather than simply trusting the first observation.

The idea is simple: Don't just ask, “Did I get FIX?” Ask: “How do I know this coordinate is correct?”

That is the difference between checking your receiver and checking your survey.

A FIXED Solution Is Only One Part of Quality Control

GNSS has made field surveying faster and more efficient, but it can also make it easy to become overly dependent on what the receiver displays.

Consider a surveyor carrying out a boundary survey. The receiver reaches FIX, and the point is stored. Before relying on that coordinate, checking against known control or independently re-observing the point can reveal a problem that the FIX status itself would never show.

FIX is important. But so are your coordinate system, antenna height, correction source, observation environment, field procedures, and independent checks.

A receiver can give you a FIX solution while the surveyor still makes a mistake.

So, the next time you see FIX on your GNSS receiver, don't just think, “I'm good to go.”

Think: “FIXED. Now, how do I verify it?”

Because getting FIX is not the end of quality control.

It is where quality control should continue.