Can RTK-GNSS Be Used in Cultural Property Surveys? Five Key Points to Know Before Introduction

In cultural property surveys, the accuracy of location information directly affects the reliability of records. If the positions of features, the layout of trenches, survey area boundaries, and the correspondence with photos or point clouds remain ambiguous, problems that are not obvious during the survey can cause major rework during data organization, report writing, re-surveys, or preservation and reuse. Against this backdrop, the use of three-dimensional measurement and high-precision positioning has advanced even in the cultural property field in recent years, and establishing environments to handle location information more reliably has become a priority. Materials from Agency for Cultural Affairs workshops show that three-dimensional measurement technologies are being introduced into buried cultural properties administration, and that consideration is being given to the precision and representation methods appropriate for each purpose.

At the same time, many practitioners have doubts about the term RTK-GNSS: “Can it really be used in cultural property surveys?”, “Can it replace surveying instruments?”, “Will it remain stable in sites with many trees or buildings?” To conclude up front, RTK-GNSS is a technology that can be sufficiently used in cultural property surveys. However, it is not万能. It is very effective for recording positions and understanding extents in open locations and for establishing reference points for photogrammetry and point cloud surveys, but in heavily obstructed environments or where strict vertical alignment is required, operational design and combination with other methods are indispensable. Whether introduction succeeds depends less on the device performance itself and more on whether you have first clarified what you want to record and to what precision.

Table of Contents

• How RTK-GNSS should be positioned in cultural property surveys

• Key point 1: View it as a technology to improve reproducibility of records

• Key point 2: Strong in open areas, weak in obstructed environments

• Key point 3: Required precision varies by survey purpose

• Key point 4: Decide the coordinate system and height handling first

• Key point 5: More effective when integrated with photos and point clouds than used alone

• How to introduce RTK-GNSS into cultural property surveys without failing

• Summary

How RTK-GNSS should be positioned in cultural property surveys

As a premise, GNSS is the general term for satellite positioning systems that determine positions using artificial satellites, and RTK is a positioning method that uses correction information to achieve high precision in real time. In public surveying, GNSS surveying, including RTK, has been used for detail surveys, establishment of control points, and field supplementary surveys. In other words, RTK-GNSS is not merely a simple position-checking tool; with appropriate conditions and procedures, it can be positioned as a technology that supports the positional basis of practical work.

Applied to cultural property surveys, the value of RTK-GNSS lies in its ability to record the locations of features and survey extents as coordinate information that can be reused later, rather than relying on ephemeral sketches or relative relationships. In cultural property work, location information is referenced over the long term—not only during the survey but in organization, comparison, confirmation, follow-up surveys in later years, coordination with surrounding development, disaster response, and public use. When positions are solid, photos, drawings, point clouds, microtopography representations, and map information acquired at different times overlay more easily, increasing overall consistency. In the case of Aso City, attention was paid to RTK-GNSS because simple surveying made it difficult to obtain precise position information for trench location records during test excavation confirmation surveys; combining high-precision position information with GIS has led to the accumulation of more accurate cultural property information.

What is important here is to view RTK-GNSS not as a universal replacement device, but as a positional foundation to enhance the reproducibility of cultural property records. From this perspective, the criteria for deciding on adoption change. Instead of trying to do everything with RTK-GNSS, it becomes easier to see which processes will benefit most from it and which should be left to other methods.

Key point 1: View it as a technology to improve reproducibility of records

In cultural property surveys, it is important not only to record what is visible on site but also to enable others to reproduce the same spatial relationships later. For example, if trench positions, feature detection points, units for managing find locations, photo shooting positions, section positions, and simple control point positions can all be referenced by the same standard across fiscal years, continuity in follow-up surveys and comparative analysis becomes much easier. RTK-GNSS is well suited to supporting such “records that can be reproduced later.”

On cultural property sites, the faster the work progresses in a day, the more likely positional recording is postponed. The more survey targets, personnel changes, photos, and handwritten notes there are, the more likely recording discrepancies will occur. In such cases, capturing major points with RTK-GNSS creates a common axis among survey notes, photos, drawings, and GIS data. Just having that common axis stabilizes the matching work during the organization phase considerably.

Cultural property surveys also connect to preservation and public use. There are many occasions after a survey where location information is useful: site explanations, consideration of preservation extents, positional understanding during disasters, and comparison with existing materials. Records with ambiguous positions lose value over time. Conversely, clear-position records are easier to reuse for other purposes. The benefit of introducing RTK-GNSS should be considered not only as time savings on the survey day but also as securing future reusability of the data, which helps avoid misjudged investment decisions.

Key point 2: Strong in open areas, weak in obstructed environments

When considering RTK-GNSS introduction, the most realistic thing to understand is the accuracy differences due to environmental conditions. RTK-GNSS performs well where the sky is open and satellite signals can be received stably. Recording trench positions in test excavation confirmation surveys, capturing points during field surveys, checking extents, acquiring control points for photogrammetry, and positioning in wide outdoor spaces are all well-matched uses. As in the Aso City case, RTK-GNSS has been introduced to improve the positional accuracy of cultural property information and utilize GIS, demonstrating practical effectiveness.

However, the situation changes in locations where satellite signals are easily blocked or reflected—near buildings, deep valleys, dense tree stands, below cliffs, or close to stone walls and high slopes. The Geospatial Information Authority of Japan explains that reflected or diffracted waves from buildings, the so-called multipath, degrade positioning accuracy, and that environments with severely limited sky visibility pose challenges for high-precision satellite positioning. In cultural property sites, areas such as temple and shrine precincts with many trees, forested mountain castle ruins, close proximity to stone structures, interiors of buildings, and river valley sites are exactly the kinds of conditions that are susceptible to these effects.

In fact, studies on RTK positioning in forests have reported cases where average errors deteriorated to the order of meters and where the FIX rate decreased. Cultural property sites are not identical to forests, but these findings serve as evidence that one should not expect the same accuracy in densely vegetated or obstructed places as in open ground. In other words, when introducing RTK-GNSS, it’s important not to make a blanket “usable or not” decision, but to distinguish “which locations on a site are likely to be stable” and “which steps should use RTK.”

Without this discernment, it is easy to misinterpret the problem as being the device itself. Concluding prematurely that “RTK is unsuitable for cultural properties” when the issue is actually site conditions is hasty. A more accurate view is that “cultural property surveys contain processes for which RTK-GNSS is highly suitable and others that require complementary methods.”

Key point 3: Required precision varies by survey purpose

The biggest reason RTK-GNSS introductions fail is treating required precision as a single monolithic requirement. Cultural property surveys cover a variety of objectives. Whether you want to grasp the broad distribution of a site, accurately record trench positions, recreate the detailed three-dimensional shapes of features, or establish standards for comparability across years will change the required precision and operational approach. Recent surveys and studies by the Agency for Cultural Affairs also indicate an approach that considers the required precision and representation methods according to the target and purpose; even for capturing surface-visible sites, research is progressing from the perspective of what level of resolution makes features interpretable.

This thinking applies directly to RTK-GNSS. For example, if you want to mark confirmation points during a fieldwalk and later organize them in GIS, it’s important to obtain reliable positions without stopping the overall site workflow. If you want reference or check points for photogrammetry or point cloud creation, you may need only a small number of points, but it’s critical to acquire high-quality coordinates at stable locations. Conversely, if faithful reproduction of fine undulations and shapes is the primary goal, it is better to combine RTK-GNSS with point cloud surveys or photogrammetry to acquire shape data rather than relying solely on RTK-GNSS.

Thus, the decision to introduce RTK-GNSS should start by clarifying whether a given task requires absolute coordinates, shape reproduction, or reproducibility at revisit. Thinking “it’s centimeter-level, so it can do everything” is not the right approach. Splitting required precision by process helps avoid both overinvestment and underestimation.

Moreover, in cultural property surveys, consistency of records is as important as precision itself. Highly detailed measurements taken on a single day become difficult to compare if records from other days follow different standards. RTK-GNSS is better suited to placing multiple records on the same coordinate axis than to perfecting minute detail reproduction. Understanding this characteristic increases satisfaction after introduction.

Key point 4: Decide the coordinate system and height handling first

When you start using RTK-GNSS in the field, it’s natural to focus on device operation and positioning stability, but in practical terms the more important thing is to decide up front which coordinate reference you will use for records. In cultural property surveys, sometimes it’s sufficient that positions align within a site; other times it is essential to overlay results with existing site maps, urban planning maps, GIS, disaster prevention information, or previous-year survey outcomes. If the coordinate system and alignment with known points are ambiguous, even high-precision measurements may become difficult to use later. In public surveying practice, there is an approach that network RTK-based topographic surveying should be conducted with reference to known points, and confirming the precision and consistency of known points is emphasized.

Height handling deserves particular attention. On site, how you handle height as well as planar position can greatly affect how results are used. If you deal with feature depth, steps, embankments, terrain changes, or alignments with sections, avoid ambiguity in height handling. Public surveying references also state that leveling may be performed when needed for elevations, indicating that height reliability should not be assumed to be uniformly guaranteed by RTK alone but should be supplemented according to purpose.

For cultural property sites, at minimum three things should be decided before starting a survey. First, will you operate in a local management coordinate system within the site, or in a coordinate system connected to a wider GIS? Second, how much vertical precision is necessary? Third, what drawings, photos, and point clouds will be overlaid in later steps? Without this clarification, measurements taken in the field may be convenient at the time but create problems during organization: “Which reference does this coordinate use?”, “It does not match results from other years,” or “Heights cannot be compared.”

The value of RTK-GNSS is determined more by how measured coordinates are recorded and reused than by the act of measuring itself. That is why design before introduction is important. The first decisions those responsible for cultural property surveys should make are not detailed device settings but rules for the recording system.

Key point 5: More effective when integrated with photos and point clouds than used alone

RTK-GNSS is most useful in cultural property surveys when integrated with photogrammetry, point cloud measurement, GIS, site photos, and drawing organization rather than used as a standalone measurement method. In the cultural property field, achievements in survey and preservation support using three-dimensional laser scanning and multi-view photogrammetry have accumulated in recent years, and Agency for Cultural Affairs materials confirm the introduction and utilization of three-dimensional measurement technologies. Within this trend, RTK-GNSS has significant value as a means of aligning the positional references of various data types rather than as a device for massive acquisition of shapes itself.

For example, even when creating a 3D model of features or terrain from photogrammetry, if the reference or check point positions are solid, the positional alignment of deliverables will be more stable. When acquiring point clouds, whether you want the entire site in a wide-area coordinate system or want to compare with data from another year greatly affects RTK-GNSS’s role. For site photos, recording shooting positions and representative points as coordinates makes later preparation of explanatory materials, reports, and public use much easier.

This integrated thinking is important because cultural property surveys are not tasks that can be completed with a single technology. Multiple objectives overlap—understanding features, grasping terrain, preserving shape, recording positions, and sharing results—and each objective may require different technologies. RTK-GNSS acts like an adhesive that connects these multiple technologies via coordinates. Expecting it to do everything alone is less realistic than incorporating it as a positional foundation to smooth the overall process; in cultural property surveys that approach yields results more readily.

How to introduce RTK-GNSS into cultural property surveys without failing

So, if you actually introduce RTK-GNSS to cultural property surveys, how should you proceed? The important point is not to try to replace all processes from the start. Begin with the processes where the benefits of location information are most visible. For example, managing trench locations in test excavation confirmation surveys, acquiring important points during fieldwalks, obtaining control points for photogrammetry, confirming survey area boundaries, and recording and organizing data in GIS are areas where the effects of introduction are easy to feel. As shown in the Aso City case, operations that combine RTK-GNSS and GIS tend to lead to accumulation of cultural property information and operational efficiencies.

Next, assess site conditions and separate locations where RTK-GNSS is likely to be stable from those where it is likely to be unstable. Decide operational rules in advance—use RTK in open areas and combine other methods in forested or near-building areas—to avoid inconsistent on-site judgments. In addition, include result-status checks in work procedures. Rather than merely recording coordinates, also record the conditions under which those coordinates were obtained; such operational records make it easier to judge reliability in later steps. Since the potential for accuracy instability in obstructed environments is supported by the Geospatial Information Authority and forest positioning research, site-specific use distinctions are essential.

Furthermore, especially at the initial stage of introduction, adopt a mindset of working backward from deliverables. If you organize in advance how coordinates taken in the field will be used in report drawings, GIS, photo organization, point cloud data, or comparison with other years, you can more easily determine the number of points, locations, and precision required. This is not a matter of devices but of operational design. Cultural property surveys are defined more by how measurements remain and are used after the moment of measurement than by the act of measuring.

Finally, it is important to avoid over-reliance on the experience or intuition of specific personnel. In the cultural property field, reliance on the skills of particular staff for managing positional information and digital technologies has been pointed out as a challenge. Therefore, when introducing RTK-GNSS, establish procedures that enable anyone to record to the same standards. When recording rules, data naming, coordinate transfer methods, and connectivity with drawings and GIS are all designed alongside device introduction, RTK-GNSS can take root as an operational foundation for cultural property surveys.

Summary

The practical answer to whether RTK-GNSS can be used in cultural property surveys is: it can be used, provided it is used correctly. RTK-GNSS delivers great power for position recording in open outdoor spaces, managing trenches and confirmation points, establishing reference points for photogrammetry and point cloud surveys, and linking with GIS. On the other hand, in places with strong obstruction from trees or buildings, highly reflective environments, or situations requiring strict vertical consistency, do not rely on it alone; assume alignment with known points and combination with other methods. The goal should not be merely to introduce equipment but to enhance the reproducibility and long-term usability of cultural property records.

In that sense, introducing RTK-GNSS at cultural property sites is not about making surveying more elaborate but about recording necessary location information more quickly and in a more reusable way. Especially at sites where a small number of surveyors must handle field checks, simple surveying, photo records, and coordinate management, high-precision positioning devices such as LRTK that can be attached to an iPhone lower the barrier to adopting positional recording in cultural property surveys. Because they make it easier to record trench positions, verify on-site coordinates, and create starting points for aligning photos and point clouds in an integrated on-site workflow, such devices are a practical option for staff aiming to achieve both labor savings and higher record quality in cultural property surveys.