How to Stabilize cm-Level GNSS Positioning｜8 Conditions to Check on Site

Demand for reliably using cm-level positioning with GNSS is rapidly increasing across various fieldwork such as surveying, construction management, as-built verification, infrastructure inspection, point cloud acquisition, asset management, and disaster investigation. When positions can be handled at the scale of a few centimeters rather than tens of centimeters, it becomes much easier to reliably link photos, drawings, point clouds, inspection records, and management ledgers, greatly improving reproducibility and reusability on site. Being able to handle high-precision positions on the spot is not only convenient but can determine the credibility of deliverables. GSSC +1

On the other hand, not every GNSS setup will automatically achieve cm-level accuracy. High-precision positioning becomes stable only when conditions such as carrier-phase-based measurements, correction information, satellite visibility, antenna performance, installation methods, and on-site verification are all met. If you base procurement solely on receiver specifications, you are likely to encounter problems in the field such as difficulty obtaining a Fix, small shifts when measuring the same point repeatedly, strangely incorrect heights, or sudden instability near buildings. These issues are not always due to the intrinsic quality of the equipment; often they are caused by missing elements in the set of conditions required for cm-level positioning to function. GSSC +2 NGS +2

What matters to practitioners is not whether cm-level positioning is theoretically possible, but whether it can be used stably on their sites. To do that, after getting a rough understanding of the mechanisms, you need to systematically eliminate conditions that tend to dominate on site. This article organizes and explains, from a practical viewpoint, eight conditions to check on site to stabilize GNSS cm-level positioning. GSSC +2 NGS +2

Table of Contents

• Why cm-level positioning becomes unstable

• Condition 1 Use a configuration that supports carrier phase and multiple frequencies

• Condition 2 Be aware of the correction mechanism and the distance from the reference station

• Condition 3 Prioritize locations with open sky

• Condition 4 Choose time windows with favorable satellite geometry and PDOP

• Condition 5 Stabilize communications and correction delivery

• Condition 6 Judge environments to avoid multipath

• Condition 7 Perform careful antenna installation and pole management

• Condition 8 Verify Fix solutions and align coordinate systems and height references

• Summary for stable field operation of GNSS cm-level positioning

Why cm-level positioning becomes unstable

To understand why GNSS cm-level positioning becomes unstable, you first need to distinguish between common code-based positioning and carrier-phase-based high-precision positioning. High-precision methods use the carrier phase, which is far more precise than code observations. Typical errors in code pseudorange are on the order of about 1 m (3.3 ft / 3 ft), whereas noise in carrier-phase observations is said to be about 5 mm (0.20 in), and this difference forms the basis of cm-level positioning. However, the carrier phase contains integer ambiguities—undetermined integer values—and unless these are correctly fixed, the observations cannot be converted into high-precision distances. In other words, cm-level positioning only exists when carrier-phase is being stably tracked and the integers are being correctly resolved, not merely when satellite signals are being received. GSSC +2 NGS +2

Moreover, correction information is crucial in high-precision positioning. In RTK-like schemes, a reference station with known position and the rover observe the same satellites, and by differencing, common errors such as satellite clock errors, orbit errors, ionospheric delays, and tropospheric delays are canceled while solving for position. Navipedia explains that RTK uses a reference station’s known coordinates and code and carrier observations to cancel major errors, yielding centimeter- to decimeter-level performance. Thus, cm-level positioning is less about an individual device’s specs and more about a system in which reference stations, corrections, observation environment, and continuous tracking work together. GSSC

Understanding this structure makes clear why precision can vary greatly by site. Poor satellite visibility, unstable corrections, abundant reflections, sloppy antenna installation, or mismatched coordinate references—though seemingly separate—ultimately disrupt integer ambiguity resolution and the reproducibility of relative positions. Practically speaking, instability in cm-level positioning is rarely due to a single cause; it is better to think of multiple small disturbances chaining together. GSSC +2 NGS +2

Condition 1 Use a configuration that supports carrier phase and multiple frequencies

The first condition is to choose a method and hardware configuration that support cm-level positioning. The important point here is not to lump everything under the name “GNSS.” Receivers intended for standalone positioning or simple setups may struggle to achieve stable centimeter-level results in the field. If you assume high-precision positioning, you need equipment capable of handling carrier phase, able to use correction information, and supporting multiple frequencies. GSSC +1

In particular, multi-frequency capability directly affects operational stability. NOAA’s guidance notes that single-frequency real-time positioning is possible, but it is slow to initialize, unsuitable for initialization while in motion, less robust, and limited in applicable baseline length, so it is not a recommended solution. In practical workflows where you often measure multiple points while moving rather than just standing still, short initialization times and resilience to reinitialization are important. In other words, to stabilize cm-level positioning, prioritize configurations that use multiple frequencies to make carrier-phase fixing more robust, rather than simply choosing equipment labeled “high-precision.” NGS +1

Also, configurations that can use multiple constellations are advantageous. More satellites increase observational freedom even in somewhat constrained skies and tend to improve geometry. While more satellites do not solve every problem automatically, a setup supporting multiple frequencies and multiple satellite systems tends to improve initialization, continuous tracking, and reproducibility on site. For cm-level positioning, how stably a device can keep a Fix in the field is more important than how impressive its spec sheet looks. NGS +1

Condition 2 Be aware of the correction mechanism and the distance from the reference station

The second condition is to be aware of how correction information is provided and the distance to the reference station. cm-level positioning presumes the use of corrections to cancel common errors, but such corrections do not work equally well at any distance. Navipedia notes that RTK service areas are generally on the order of about 10-20 km (6.2-12.4 mi) around a reference station, and as a rover moves away from the reference, especially tropospheric error correlations tend to break down first. In other words, corrections are not omnipotent; they work best when the reference and rover are reasonably close. GSSC

Therefore, when cm-level positioning seems unstable on site, don’t assume it’s just a communications issue—also consider the correction scheme and the distance to the correction source. For example, when traversing a large site from one end to the other or measuring in environments relatively far from the reference, correction effectiveness can vary by location. Even if corrections appear to be received, if common errors are not sufficiently canceled, Fixing can be difficult and accuracy can fluctuate. GSSC +1

In practice, using corrections without understanding reference distances or the assumptions of the service will make it hard to see why only some points are unstable. To stabilize cm-level positioning, consider whether the whole site is within a reasonable range for the correction method, or where to anchor references when working over a wide area. Treat correction information not as mere data traffic but as a foundational condition supporting accuracy. GSSC +1

Condition 3 Prioritize locations with open sky

The third condition is to prioritize locations with wide-open sky. GNSS receives signals from satellites, so the more open the sky, the better. Buildings, trees, bridges, retaining walls, and slopes can block some satellites or create biased observation conditions where only one sector of the sky is visible. Navipedia also states that RTK requires continuity of observations and that in urban environments, obstacles increase constraints on reinitialization. Thus, sky visibility directly affects stability for cm-level positioning. GSSC

It is important not to judge sky visibility by feel alone. Even if the zenith is clear, if one side is closed by tall buildings or slopes, satellite geometry can degrade. Trees are similar: during leafy seasons, branch and foliage obstruction increases and reception conditions can be entirely different from winter. If you want stable cm-level results, inspect sky conditions before measuring and decide whether to complete observations at that spot or combine it with a nearby open location. GSSC +1

Near urban structures, not only does satellite count drop, but continuous tracking is more likely to be interrupted. Carrier-phase-based high-precision positioning requires continuous phase tracking, so even slight obstruction can cause loss of lock. To improve stability, it is more practical to organize procedures around reference points with good sky visibility rather than trying to force measurements in marginal locations. GSSC +1

Condition 4 Choose time windows with favorable satellite geometry and PDOP

The fourth condition is to choose time windows when satellite geometry and PDOP are favorable. For cm-level positioning, not only the number of satellites but also their geometric configuration matters. NOAA describes DOP as an index of how satellite geometry affects position error; PDOP represents three-dimensional position uncertainty, and lower is better. Low PDOP corresponds to satellites being widely distributed across the sky. NGS

Therefore, it is natural that the ease of positioning at the same site can vary by time of day. If fixes were easy in the morning but unstable in the afternoon, or behavior differs on another day, satellite geometry may be the cause. Mistakenly attributing such changes to equipment malfunction or communications can lead to the wrong countermeasures. To stabilize cm-level positioning, don’t wait to check numbers after the fact—if possible, review satellite geometry and PDOP trends in advance and plan to work during favorable windows. NGS +1

For critical or hard-to-remeasure points, selecting the time window can directly affect deliverable quality. Field crews often proceed assuming they can always measure equally, but cm-level positioning is not that uniform. In tighter conditions, simply changing the time can improve results. PDOP is only one indicator, but knowing that lower values are generally geometrically advantageous will noticeably improve on-site judgment. NGS

Condition 5 Stabilize communications and correction delivery

The fifth condition is to stabilize communications and correction delivery. cm-level positioning presumes that correction information is delivered stably. In the field, however, you can encounter situations where voice calls connect but data communications are unstable, delays increase with slight movement, or corrections drop and Fix recovery takes a long time. NOAA warns that places with strong cellular voice may still have intermittent data and that if Fixing takes much longer than usual, incorrect cycle counting can lead to insufficient accuracy. NGS

In practice, it is more important that corrections remain stable throughout the working period than that they connect briefly. Even if you get a Fix initially, if the system becomes unstable every time you move, it is unsuitable for multi-point surveys or workflows linking point clouds and photos. On large sites, slopes, retaining structures, forests, or urban areas where communications vary, think of the places to measure important points and the places to check positioning status separately. NGS +1

Also, visibility of the correction link and stable correction quality are different things. Communication delays or intermittent reconnections can make it appear numerically that high-precision positioning is happening while reproducibility of adopted values degrades. To stabilize cm-level positioning, monitor correction status on site; for critical points, wait a bit, remeasure, and verify against known points. Treat communications not as an auxiliary matter but as part of cm-level positioning itself. NGS +1

Condition 6 Judge environments to avoid multipath

The sixth condition is to judge environments to avoid multipath. Multipath occurs when satellite signals reach the antenna via reflected paths from buildings, ground, water, metal, vehicles, fences, etc., in addition to the direct path. Navipedia explains that multipath occurs when signals arrive via multiple routes and becomes more significant near reflecting structures. NOAA’s guidelines also note that trees, buildings, large vehicles, water, and metal objects can be multipath sources, and that in real-time positioning this is difficult to model on site, sometimes producing apparently precise but misleading results. GSSC +1

What makes multipath troublesome is that receivers don’t always signal a clear fault. You may have a Fix and seemingly good RMS, yet on remeasurement the same point differs slightly or known points fail to align. NOAA warns that multipath can cause incorrect integer ambiguity resolution, producing large errors especially in the vertical component. If horizontal values look reasonable but height is odd, suspect multipath. NGS

The primary countermeasure is to avoid using locations likely to have strong reflections for critical points. Avoid locations along buildings, next to metal fences, near parked vehicles, beside water, in areas with many glass surfaces, and under trees; simply moving a little to a more open spot can improve results. If you must measure near such features, change times and remeasure, shift the point slightly for multiple checks, or secure references at better locations to fill in—these approaches are safer. In high-precision GNSS, the skill of knowing where not to measure is as important as the measuring technique itself. NGS +1

Condition 7 Perform careful antenna installation and pole management

The seventh condition is to perform careful antenna installation and pole management. In cm-level positioning, the final few centimeters are determined by installation quality. NOAA recommends that rover poles be straight and free of bends, that stabilizing fixed-height poles, bipods, or tripods be used when appropriate, and that bubble level adjustments be checked before observation. They also describe a practical method of rotating the pole 180 degrees and observing twice to cancel plumb errors when the pole cannot be fully trusted. NGS +1

High-precision GNSS assumes the antenna is directly above the point you actually want to measure. If a pole is slightly tilted, a tripod is poorly set, instrument height is entered incorrectly, or the antenna reference point is misidentified, centimeter-level accuracy can be lost easily. What's worse, numbers may appear clean, so such errors are hard to detect on site. In high-precision positioning, careful installation is not something to do “if there’s time”; it is part of the accuracy itself. NGS +1

Also, antennas have phase centers and phase center variations; the visible center and the electrical observation center do not always perfectly coincide. NOAA notes that antenna phase centers vary with satellite elevation and azimuth and should be handled using a phase center variation model. Thus, in cm-level positioning antenna quality and how it’s handled are more important than might be imagined; comparing only base unit performance is insufficient. NGS +1

On site, it is important not to rush installation for critical points. While the ability to collect many points in seconds is attractive, for fixed points, control points, and locations serving as anchors for photos or point clouds, carefully confirming pole verticality, instrument height, and installation position will ultimately improve the reliability of all work. In cm-level positioning, observing installation basics matters more than device sophistication in the end. NGS +1

Condition 8 Verify Fix solutions and align coordinate systems and height references

The eighth condition is not to overtrust the Fix solution and to verify it, and at the same time to align coordinate systems and height references from the start. NOAA notes that if Fixing takes much longer than usual, incorrect cycle resolution may result in insufficient accuracy, and some data collectors may not clearly indicate a bad Fix. In other words, a Fix indication is a necessary condition but not sufficient. For important points, include repeat measurements of the same point, checks against known points, and repeated observations after some time to confirm the solution is truly reproducible. NGS +1

Also, do not postpone organizing coordinate systems and height references in cm-level positioning. NOAA explains that ellipsoidal heights derived from GNSS need a geoid model to be related to the practical height system used in the field. So even if horizontal positions align, height differences can arise not only from positioning errors but from differences in reference surfaces. When overlaying point clouds, drawings, known points, construction management data, and past deliverables, failing to decide which coordinate and height systems to use at the outset can lead to major rework. NGS +1

Furthermore, the receiver’s internal computations and display settings do not always match the coordinate system you need. Values may look smooth on site but discrepancies can become apparent the moment you overlay them on drawings or point clouds prepared under another reference. Therefore, before starting measurements, verify consistency with known points or comparable references and ensure that the settings you will use that day truly match your deliverable standards. Because high-precision GNSS deals with centimeter-level domains, reference mismatches become relatively major problems. NGS +1

Summary for stable field operation of GNSS cm-level positioning

To stabilize GNSS cm-level positioning, first understand the mechanisms, then systematically eliminate error sources. Assume high-precision positioning using carrier phase and corrections; be mindful of the distance to correction sources; choose open-sky locations; work during times with favorable PDOP; stabilize communications; avoid multipath; be meticulous about antenna installation; and finally verify Fix solutions and align coordinate and height references. Following this sequence will greatly improve the reproducibility of cm-level positioning. NGS +3 GSSC +3 NGS +3

In practice, what matters is not the accuracy stated on spec sheets but the accuracy you can reproduce on site. The value of high-precision GNSS is reproducibility: can anyone measure it the same way, will remeasurement on another day align, and can you confidently connect photos, point clouds, and drawings? In that sense, cm-level positioning is not just an equipment selection issue but a design of on-site operations. NGS +2 NGS +2

If you want to introduce cm-level GNSS in a form that is easier to use on site, or integrate high-precision positioning naturally with photos, point clouds, and field records, consider devices such as iPhone-mounted high-precision GNSS systems like LRTK. If you want to make high-precision positioning part of routine field records and asset management rather than restricting it to specialist tasks, such solutions can be practical options.