Can GCP Placement Be Reduced? Six Cautions When Using Network RTK

Many practitioners think that introducing network RTK will speed up on-site positioning and coordinate verification and reduce the burden of control point work and GCP placement that previously required much effort. Especially in surveying, photogrammetry, as-built management, and construction management, manpower shortages and pressure to shorten schedules are strong, and the demand to secure accuracy with fewer people grows year by year. In that context, it is natural to expect that using network RTK could greatly reduce GCPs, or in some cases make them unnecessary.

However, the first point to note is that network RTK is not a万能 solution that can replace all the roles of GCPs. GCPs are not placed merely to provide coordinates. They have multiple meanings: aligning deliverable coordinates, ensuring external accuracy, validating analysis results, and building consensus among stakeholders. Therefore, while there are situations where network RTK can reduce GCP placement, operating without clarifying the conditions under which reduction is acceptable can lead to errors surfacing in downstream processes, difficulty in explaining deliverables, and increased risk of re-surveying.

What matters in practice is not simply asking whether GCPs can be reduced. It is important to separate which process, for what purpose, and to what extent GCPs can be reduced. Some roles are easy to substitute with network RTK, while others should remain as verification points until the end. Misjudging this can make a site appear to progress quickly at first but later consume extra time for quality assurance and deliverable organization.

This article is for practitioners searching for “network RTK GCP.” It organizes the thinking for reducing GCP placement and the six easily overlooked cautions when actually operating. Focusing on points where on-site judgments are likely to be wrong rather than mere theory, it explains what to check before introduction, the difference between situations where reduction is acceptable and those requiring caution, and realistic thinking to improve efficiency without degrading quality.

Table of contents

• Can GCP placement really be reduced?

• Caution 1: Confirm coordinate systems and consistency with known points first

• Caution 2: Do not overtrust network RTK communications and correction conditions

• Caution 3: Even if Fix is achieved, it does not necessarily guarantee accuracy

• Caution 4: The effect of GCP reduction varies greatly with site environment

• Caution 5: Do not cut verification points required for deliverables

• Caution 6: If you don’t standardize operating procedures, labor savings can backfire

• Summary

Can GCP placement really be reduced?

In conclusion, using network RTK can certainly reduce the number of GCPs and the workload of placing them. However, “can be reduced” here does not mean “uniformly unnecessary.” Reduction is possible only when on-site conditions, required accuracy, how deliverables will be used, and verification methods are organized.

First, GCPs have multiple roles. One is to provide a coordinate reference on-site. Another is to check whether the acquired data is placed correctly. They also serve as a basis for explaining to clients and stakeholders why the results can be trusted. Network RTK can greatly streamline the role of providing coordinates, but it cannot always fully take over the validation and accountability roles.

For example, for simple site surveys, position confirmation for construction, setting out temporary structures, and preliminary checks for as-built management, network RTK may allow operation with fewer control points than before. On the other hand, for tasks such as photogrammetry or creating 3D deliverables where explaining external accuracy is important, it is safer to keep separate verification points or comparisons with known points even if you reduce the number of GCPs. In short, the decision to reduce GCPs must include not only the measurement itself but also how you will demonstrate quality.

A common misunderstanding is to assume that because network RTK can observe points, the accuracy of the entire deliverable is therefore fine. In reality, single-point observation accuracy and the alignment accuracy of an area or whole model are different matters. Even if measurements show good values at observation time, biases can appear across the working area. Also, intermittent communication loss, re-initialization effects, surrounding obstructions, and differences in reception conditions by time of day can combine locally and result in discrepancies that are hard to notice on-site but become apparent in downstream processes.

Therefore, the idea of reducing GCPs is reasonable, but reduction must not be the objective itself. The objective is to optimize on-site workload while maintaining required accuracy and explainability. If you invert that order, apparent labor savings at first can lead to inefficiency due to re-checks and rework. The next chapters detail six cautions to avoid such misjudgments.

Caution 1: Confirm coordinate systems and consistency with known points first

When considering reducing GCP placement with network RTK, the first thing to check is the consistency of the coordinate system. This is unglamorous but the most important prerequisite. If you start operating with this unclear, no matter how many observations you take or how advanced the receiver environment, your results will not be stable.

On site, plane rectangular coordinates, how elevations are handled, management methods for existing control points, and the coordinate bases of past drawings can coexist. It is not uncommon for each person in charge to understand them differently or for the origin of past materials to be unclear. If you observe with network RTK under these conditions, coordinates may appear to be obtained on the spot but will shift when overlaid on existing drawings or past deliverables. Then it becomes hard to separate whether the problem lies with the observation equipment or correction information, or with the original reference.

If you want to reduce GCPs, you should spend more time on initial consistency checks. Specifically, decide on the coordinate reference to be used on site, compare with known points and existing markers, and align stakeholders on which coordinate values are to be regarded as correct. Network RTK is convenient but will not automatically correct for on-site local rules or ambiguities in old deliverables. Omitting comparisons with known points will cause any mismatch in the reference to be reflected directly in the deliverables to the same extent as you reduced GCPs.

Also, in sites considering GCP reduction, the relative importance of known points increases. If you reduce numbers, each point becomes more significant. Confirming multiple reference points and ensuring consistent coordinate interpretation across the site makes it easier to avoid unnecessary GCP placement. Conversely, on sites with ambiguous references, it is safer not to reduce them rashly.

One often overlooked issue is the handling of elevation. Even if horizontal positions match, differing vertical references can make deliverables difficult to use. For tasks where elevation alignment is important—terrain assessment, as-built verification, drainage and structural considerations—issues tend to appear more on the elevation side than the horizontal. When aiming to reduce GCPs, do not postpone confirming vertical reference.

In short, if you want to save labor with network RTK, spend time preparing reference alignment before observation. While on-site installation work may be reduced, verification of reference consistency should not be. Only by doing this thoroughly does GCP reduction become a safe efficiency measure.

Caution 2: Do not overtrust network RTK communications and correction conditions

Because network RTK obtains high-precision positions by receiving correction information, it strongly depends on communications and correction conditions. Underestimating this can make a site less stable despite fewer GCPs, increasing verification tasks.

Field personnel tend to feel reassured when three things are met: reception is available, corrections are being applied, and the display seems fine. But in practice, that is not enough. Communications can be temporarily unstable, correction reconnections may occur intermittently, and adopting observation values immediately after initialization can cause variability over time even when measuring the same location. Such variability can be difficult to see in single observations and only become apparent when comparing later.

Sites with many GCPs can absorb such local instability later. But in sites where GCPs are reduced, each observation has a larger impact on the deliverables. In other words, managing network RTK conditions becomes more important than before.

What is needed is to treat the communication environment as a precondition. In mountainous areas, near slopes, close to structures, on sites with many temporary fences, or in narrow urban spaces, both communications and reception tend to be unstable. Rather than discovering problems after arriving on site, anticipate communication conditions and obstructions before work, and if necessary adjust observation timing or work positions.

Also, the duration for which corrections have been applied should not be underestimated. Immediately after connecting or re-initializing, the display may appear resolved, but stability assessment may be insufficient. If you rush to adopt values at this stage, some points may show different accuracy. If you are reducing GCPs, it is even more necessary to standardize adoption conditions as site rules. If adoption judgments differ by person, data quality variability is unavoidable.

Network RTK can yield significant labor savings if used appropriately. But that assumes an understanding that communications and corrections are not always stable. Because it is convenient, you must adopt an attitude of checking whether it is functioning correctly. On sites aiming to reduce GCPs, the quality of these checks determines deliverable stability.

Caution 3: Even if Fix is achieved, it does not necessarily guarantee accuracy

A common occurrence on sites using network RTK is the judgment “Fix, so there’s no problem.” Fix is indeed an important indicator, but by itself it does not guarantee the overall reliability of deliverables. This misunderstanding is particularly dangerous when considering GCP reduction.

Fix is a sign that the solution has reached a stable state based on satellite observations and correction information. However, whether being in Fix is sufficient for the task’s requirements is a different matter. Surrounding obstructions, reflections, observation posture, instability immediately after re-initialization, and short-duration observations can all cause subtle biases even in Fix state. Moreover, such biases are often hard to see on site.

For example, if reception conditions are poor in one corner of the site, that point may shift slightly. As a single point it may appear acceptable, but when comparing the whole area, longitudinal and cross sections, or overlays with existing structures later, it may show alignment failures. With many GCPs you might notice the anomaly, but in reduced setups it is easy to miss.

The important point is to treat Fix as one of the adoption conditions but not the sole criterion. In practice, combining repeated checks at the same point, verification with known points, re-observation separated by time, and consistency checks across the working area produces data you can trust. When reducing GCPs, avoid operations that end with “it’s Fix, so we’re done.”

From a personnel training perspective, it is also necessary to share the correct meaning of Fix. Some sites proceed with observations after looking only at the display state without sufficient stability checks. That allows individual experience differences to become quality differences. If labor savings result in a system that only experienced personnel can operate stably, the effort defeats its purpose.

Reducing GCPs is also, in other words, raising the site’s self-checking capability. Fix is a convenient indicator, but by itself it is not quality assurance. Holding multiple bases for trusting observation results is a safety measure when reducing GCPs.

Caution 4: The effect of GCP reduction varies greatly with site environment

Whether you can reduce GCP placement with network RTK is influenced more by the site environment than by theory. Ignoring this and applying a uniform operation often leads to failure. It is especially risky to take a method that worked on an open site and apply it unchanged to different site conditions.

For example, in a site with a wide sky view, few tall surrounding structures, and stable communications, the advantages of network RTK are easier to realize. In such places, you may be able to work efficiently with fewer control or verification points than before. Conversely, in areas with dense trees, valley terrain, close proximity of structures, or skewed sky views, reception conditions vary more and local errors are likely.

In addition, for tasks involving photogrammetry or 3D modeling, site environment impacts not only observations but post-processing and model quality. Even with stable on-site positioning, variations in target shape, shooting conditions, shadows, obstructions, and surface conditions can introduce variability in deliverables. Therefore, distinguish between situations where network RTK alone suffices for positioning and those where combining GCPs or verification points is preferable.

Moreover, even at the same site the judgment can change depending on the task objective. A rough overview for provisional planning and records intended for as-built verification or future comparison have different requirements for explainability. The former may allow reducing GCPs with little practical issue, but the latter benefits from retaining verification points to increase later reusability. Thus, the decision to reduce GCPs must consider not only site environment but also what the data will be used for.

What’s important here is the perspective to judge in advance whether a site is suitable for GCP reduction. Consider whether reception will be easy, whether communications will be stable, whether known points are usable, whether the working area is extensive, and how much deliverable explanation is required. Clarifying these aspects beforehand will reveal sites where reduction is not advisable. Omitting this judgment leads to inconsistent decisions after arriving on site and increases ad hoc measures.

Network RTK is a powerful tool, but it does not produce the same effect in every site. To succeed in GCP reduction, you must evaluate not only technical performance but also compatibility with site conditions.

Caution 5: Do not cut verification points required for deliverables

The biggest caution when attempting to reduce GCPs is not to confuse cutting placement points with cutting verification. If you get this wrong, operations may be faster but the deliverable’s reliability will weaken.

In practice, there are broadly two concepts for necessary points on site. One is points to provide positions and the other is points to verify results. Network RTK can reduce the burden of the former, but if you also cut the latter, you remove means to confirm the validity of results. This is especially problematic for work that needs later explanation to third parties.

For example, if you produce a 3D dataset or planimetric deliverable and want to demonstrate that it truly aligns with the site, independent verification points are necessary. If all points were acquired under the same conditions and evaluated under those same conditions, internal consistency may appear, but external accuracy may not be sufficiently demonstrated. When reducing GCPs, it is even more important to retain at least a small number of verification-only points.

These verification points are not about quantity alone. They must be meaningfully placed and used. Include not only site edges but also central areas and locations with challenging conditions so biases across the work area are visible, and do not verify only conveniently located points in the same workflow. The aim of reducing GCPs is labor savings, but weak placement of verification points can lead to re-surveying or additional explanation later.

Leaving verification points also protects on-site personnel. If someone later questions coordinate alignment or positional differences, you can explain what checks were made at the time. On site, after a problem occurs, you may be asked “why did you decide that number of points was sufficient?” Whether you have verification records through these points greatly affects how easily you can explain.

Reducing GCPs does not mean lowering quality. Rather, because you operate with fewer points, you must explicitly decide what will remain for verification. Intentionally separating positioning points from verification points is an important concept when using network RTK.

Caution 6: If you don’t standardize operating procedures, labor savings can backfire

Operations that reduce GCP placement using network RTK will not last if they depend on personal intuition or experience. Initially, a skilled person may manage well, but when the job is handed to another, accuracy and judgments can fluctuate. Therefore, to truly convert labor savings into reliable deliverables, standardize observation and verification procedures.

A common on-site problem is that adoption criteria differ by person. One person may begin observing immediately after correction connection, while another may wait until it stabilizes. One may verify known points every time, another may only do it initially. Such differences seem small, but in operations with reduced GCPs they manifest as quality differences.

Standardization should not be only about difficult theory. Practical procedures to document include: what to check before observation, which states to use as adoption criteria, in what situations re-observation is required, how frequently to compare with known points, and what to inspect before finishing site work. When these are documented, quality is easier to maintain even if personnel change.

Further, standardization speeds judgment. On site you must make repeated decisions under time pressure. Relying on individual experience increases hesitation and, ultimately, task time. Conversely, shared criteria enable quick decisions about how many GCPs to leave today, whether additional checks are needed, or whether it is acceptable to proceed with network RTK alone. This is not just quality management but a mechanism that supports site speed.

Standardize recording methods as well. If you record which known points you checked, when stability was achieved, and which locations had poor conditions, downstream verification becomes easier. In operations that reduce GCPs, being able to trace on-site decision reasons later is important.

Labor savings are not merely reducing work volume. Only when a reproducible state is created that keeps results within acceptable bounds regardless of who performs them does efficiency become practical. Don’t let GCP reduction with network RTK remain a one-off trick; institutionalize it as standard site procedure to achieve reliable outcomes.

Summary

Using network RTK can indeed reduce the burden of GCP placement in some situations. Especially for on-site position checks, simple surveying, and pre- and post-construction coordinate checks, you may achieve required accuracy with less effort than before. However, because GCPs also play important roles in verification and accountability, it is dangerous to think simply “we have network RTK, so we can reduce GCPs.”

To avoid mistakes in practice, you must first confirm coordinate systems and consistency with known points, not overtrust communications and correction conditions, not rely solely on Fix, judge compatibility with the site environment, retain verification points required for deliverables, and standardize operating procedures. Keeping these six points in mind makes the decision to reduce GCPs a rational choice that preserves quality rather than a matter of intuition.

With continuing manpower shortages and schedule pressures, how to streamline control point work and coordinate checks greatly affects daily productivity. To run network RTK–based operations at the site level without strain, the key is to verify what is necessary and reduce only where appropriate.

If you want to proceed with setting control surveys, known point checks, pre-construction positioning, or coordinate rechecks with as few people as possible, tools like LRTK—a smartphone-mounted GNSS high-precision positioning device—can be effective. For initial positional checks before large-scale preparation, initial positioning to decide whether full GCP placement is needed, or quick site surveys to capture key points, LRTK can lighten both decision-making and field work. Rather than merely reducing GCPs, when you want to streamline overall site flow while maintaining required accuracy, LRTK can be a practical option for field work.