How to Improve the Positional Accuracy of Location Records of Cultural Properties with RTK｜4 Foolproof Steps

Table of Contents

• The Importance of Recording the Locations of Cultural Heritage Using RTK

• Fundamentals to Grasp Before Using RTK for Cultural Heritage Documentation

• Step 1 Organize what to record and the required accuracy

• Step 2 Develop an observation plan tailored to local conditions

• Step 3: Perform reproducible on-site position recording

• Step 4 Design how to organize, store, and share recorded data

• Common mistakes when recording cultural heritage locations with RTK

• Approach to Balancing Efficiency and Accuracy in Cultural Heritage Documentation

• Summary

The Importance of Recording the Locations of Cultural Properties with RTK

In the field of cultural property survey, conservation, management, restoration, and public utilization, the accuracy of positional information determines the overall quality of the work. Information involving positions—such as the location of remains, the arrangement of stone blocks and foundation stones, the boundaries of excavation areas, the placement of signs, the recorded locations of damage, and the points where photographs and point-cloud data were captured—is far more numerous than one might imagine. If these are handled only with ambiguous plans or visual, sight-based records, it can become impossible to correlate them with the actual site when reviewed later, necessitating re-surveying or re-measurement.

Records related to cultural properties should not be something that only needs to be understood on the spot. Even months or years later, or after being handed over to the next person in charge, it must be possible to correctly reference the same location. There are many situations in which positional accuracy matters: comparing before and after restoration, tracking changes over time, disaster response, confirming protection boundaries, and coordinating with surrounding facility development. For these reasons, location records for cultural properties must be created using methods that can preserve “what was where” with high reproducibility.

Attention has turned to RTK. RTK is a technique that performs high-precision positioning on-site and makes it easier to capture recorded subjects at the centimeter level (cm level accuracy, half-inch accuracy), and its use is expanding at many sites. In the cultural heritage field as well, it is characterized by being well suited to a variety of tasks, such as geotagged photography, creation of plan views, simple assessment of current conditions, checking positional relationships with surrounding facilities, and coordinate alignment with point clouds and three-dimensional data.

However, using RTK does not automatically produce accurate records. Conditions at cultural heritage sites—trees, stone walls, buildings, temporary structures, slopes, narrow plots, and so on—often make positioning conditions inconsistent, and there are precautions that differ from those at ordinary civil engineering sites. In addition, cultural heritage work has unique constraints such as difficulty touching the objects directly, inability to change installation positions, prohibition on excavation or relocation, and limits on working hours. For these reasons, it is important to design the positioning concept, observation plan, field operations, and data processing as an integrated workflow.

This article clearly explains four practical procedures you should understand to improve the positional recording accuracy of cultural heritage using RTK. Rather than simply describing how to operate the equipment, it organizes why accuracy can be unstable, where differences in recording quality emerge, and what should be documented to avoid problems in downstream processes. The content will be useful not only for those planning to introduce RTK but also for those already using it who feel there is variability in the quality of their records.

Essentials to Know Before Using RTK in Cultural Heritage Documentation

To successfully record the positions of cultural heritage using RTK, you must first correctly understand what "high precision" means. In the field, the word "accuracy" tends to be treated as a single concept, but in reality there are several perspectives. One is absolute accuracy: how close an observed point is to its true position. Another is repeatability: how consistent the values are when the same point is measured again. Furthermore, the relative consistency of how stable the positional relationships among multiple points are is also important.

When recording the locations of cultural properties, it is essential to consider these three aspects separately. For example, if you want to overlay the data with other map information or design information in the future, absolute positional accuracy becomes important. On the other hand, if you want to carefully preserve the spatial relationships of features within a survey plot, maintaining the relative relationships between points is the priority. Also, on sites where surveys are conducted in multiple sessions, reproducibility that allows comparison between previous and current measurements is extremely important.

Another important thing to understand is that RTK is not foolproof. Sky visibility, the reception environment, the availability of correction data, observation time, how survey points are taken, and the operator's procedures all have a major impact on accuracy. At cultural heritage sites, surrounding trees and buildings can block satellite reception, confined spaces can cause reflections, and it can be difficult to place a positioning point directly above the subject; therefore, treating these sites the same way as the open sites of civil engineering work can result in larger errors.

Furthermore, in cultural heritage recording, consideration must be given to how the objects themselves are handled. For example, decisions are required about how far the corners of stone structures or foundation stones should be regarded as representative points, which line should be used to record the position of the boundary of a collapsed soil layer, and to what extent irregular surface undulations should be captured as discrete points. In other words, improving accuracy with RTK is not simply about increasing the numerical precision of positioning values; it also involves appropriately selecting points that are meaningful on site and preserving them in a form that allows that meaning to be interpreted later.

If this premise is not shared, problems will arise in the field such as "the equipment is highly accurate but hard to use," "there are numbers but they are difficult to turn into useful results," and "data from different days do not match." Conversely, if the measurement purpose, required accuracy, site conditions, and recording methods are organized from the outset, RTK can become a means to greatly improve the quality of cultural heritage documentation. From the next chapter, we will look at the four steps, in order, to avoid failures in practice.

Step 1 Organize the items to be recorded and the required accuracy

When you want to improve the positional accuracy of cultural heritage records using RTK, the first thing to do is not to prepare equipment. What you need first is to clearly define what you want to record and to what level of accuracy. If you go into the field with this unclear, you may spend more time than necessary or, conversely, lack the information you need, resulting in lower quality and efficiency.

There is a wide variety of items that may be subject to position recording at cultural heritage sites. Corners of excavation units, reference lines, outlines of archaeological features, find spots, positions of stone blocks and pillar foundations, locations of damage, positions of protective fences and information boards, and locations from which survey photographs were taken — even within the same site, the required level of accuracy varies depending on the item being recorded.

For example, points related to the boundary of a protected area or to future maintenance plans require an accuracy that is consistent with other maps and geographic information. On the other hand, if the primary objective is to understand spatial relationships within the site, mutual consistency may be prioritized over absolute coordinates.

What’s important here is to explicitly state the intended use of the records for each object. Whether you are preserving locations for restoration, producing plan views for an investigation report, using them for future comparative observations, or aligning photographs and point clouds will change the required observation density and checking methods. If you try to measure everything uniformly with the same procedure despite different uses, you will lack necessary information where it’s needed and increase labor where it’s not.

Also, for cultural properties, it is necessary to decide in advance the definition of "what will be considered the representative point." For example, for stone materials, whether to take the center or the corner; for archaeological features, whether to take the upstanding line or the outer edge; for wall surfaces, whether the base or the top edge; and for damaged areas, whether to take the widest part or the center point. If you begin work without deciding this, recording standards will vary by person in charge, and later diagramming or comparisons will not be consistent. Especially when a survey is conducted by multiple people or measurements are taken over multiple days, it is essential to share the rules for representative points as a record sheet or an operational memo.

Additionally, in practice it is important not to set the required level of accuracy too high. The attitude of striving for high accuracy is valuable, but placing overly strict accuracy targets relative to site conditions and the nature of the subject can actually make operations unstable. Cultural heritage often has irregular shapes, and the boundaries of the subject frequently involve interpretation, so making only the measurements extremely detailed does not necessarily improve the overall quality of the results. What is needed is to secure sufficient accuracy for the purpose and, on that basis, maintain reproducibility and operability.

What should also be organized here is the form of the deliverables. Depending on whether you retain only points, organize them as lines or surfaces, link them with photographs or point clouds, or manage them on a map, the attribute information you need to assign in the field will change. If you design from the start the information that will be needed later—such as number, name, type, photograph date and time, observer, remarks, and object description—post-fieldwork organization becomes considerably easier. Conversely, if you only capture positions in the field and try to assign meaning later, you will be unable to match them with photographs, and verification will take time.

In other words, the essence of Step 1 is to design what will be measured before using RTK. In cultural heritage documentation, high precision can only be achieved by clarifying not just the numeric position but also the meaning of the subject, the definition of representative points, and the connection to the deliverables. If this preparation is done thoroughly, the next step—the observation plan—will also be realistic and feasible.

Step 2: Develop an observation plan tailored to local conditions

Once the recording targets and required accuracy have been clarified, the next step is to create an observation plan that takes local conditions into account. The success or failure of RTK is not determined solely by actions taken after arriving on site; it can be greatly affected by thinking in advance about where, when, in what order, and how measurements will be taken. On cultural heritage sites, differences in conditions from place to place are greater than at typical surveying sites, so skipping this step tends to lead to greater variability in accuracy.

The first thing to check is the overhead environment. Because RTK is affected by the reception of satellite signals, stability differs between places with wide open sky and places surrounded by trees or structures. At cultural heritage sites there are often locations with poor reception conditions, such as ruins within forests, areas around castle stone walls, under the eaves of buildings, narrow passageways, and plots enclosed by earthen embankments. If you have drawings or photos before entering the site, check them, and if possible identify, as soon as you arrive, the locations where reception is easy and where it is difficult to reduce unnecessary or impractical observations.

Next to consider is how to establish reference points. In cultural heritage recording, rather than recording every point in one go during the main session, it stabilizes later processing to first fix reference points and checkpoints that can be commonly referenced across the entire site. By recording the four corners of the survey area, the main partition lines, representative points of immovable structures, and so on in advance, it becomes easier to match point clouds, photographs, and notes acquired later. Also, when work is split across multiple days, it is important to choose points that are easy to re-identify so the same references can be restored on return visits.

The order of observations is also unexpectedly important. Generally, stabilizing the whole operation is easier if you first secure reference points at locations with good reception conditions and then proceed to the target measurements from there. If you start out in a location with poor conditions, you can end up wasting time without being able to judge the positioning status, and the operator’s sense can become unstable. Simply performing a status check and a quick re-measurement check first at an open area, and getting a feel for that day’s observation tendencies before moving to the main site, will reduce the likelihood of failure.

Also, consideration of workflow and movement routes is indispensable at cultural heritage sites. In areas with access restrictions, zones where foot traffic or pressure should be avoided, places where visitor routes intersect, or where footing is poor, not only measurement points but the workers’ movement itself becomes constrained. If you prioritize higher accuracy to the point of trying to measure from strained or awkward postures, the way you pick target positions can become sloppy and holding the equipment unstable, which can actually reduce accuracy. Choosing locations where you can maintain a safe, comfortable posture and repeat the same measurement approach will, as a result, improve the quality of the records.

Moreover, weather and the time of day cannot be ignored. Work at cultural heritage sites is often conducted outdoors, and the flow of people nearby, lighting conditions, and ease of working change depending on the time of day. Including morning dew, muddy ground, strong winds, shifting shadows, and dealing with visitors, it is important to determine the times when stable observations can be made. Even if position recording alone seems like it could be finished in a few minutes, once you include verifying the subject, taking photographs, filling out record forms, and coordinating with the surroundings, the time required increases. If the schedule is too tight, you may skip confirmatory measurements and later be unable to detect errors.

In an observation plan, verification methods should also be decided in advance. For example, re-measure important points after a time interval, measure the same reference point across different days, check the distance relationships among multiple points, and record the target location together with photographs. Because records of cultural properties are difficult to redo, it is essential to design the work so that what can be verified on site is completed on site. If verification rules are determined at the planning stage, quality remains stable even when personnel change.

Thus, in Step 2 it is important to consider the site not in terms of "whether it can be measured" but in terms of "how it can be measured reliably." RTK is a high-performance method, but at cultural heritage sites the quality of advance planning is directly reflected in the quality of the results. Only by designing the reception environment, control points, movement routes, sequence, and verification methods does high-precision position recording become practical.

Step 3: Perform reproducible on-site position recording

Even when preparatory work and observation plans are in place, if the recording procedures on site are not standardized, the quality of positional records will not be consistent. In recording the positions of cultural properties, the delicacy of the objects and the complexity of site conditions mean that even slight differences in procedure can affect the results. Therefore, in Step 3 it is important not merely to measure points, but to carry out observations that can be reproduced with the same approach by anyone performing the work.

First, be aware that you should record the target when the positioning readings are in a stable state. On site people tend to rush and record points one after another, but if you take the displayed values at face value and proceed, you can get variability in the points later. Especially under trees, near buildings, along slopes, or beside stone walls, the condition may appear stable on the surface yet subtle oscillations can remain. What matters is not a single reading but the stability over a period of time and the reproducibility when you re-measure the same point.

With cultural heritage objects, it is often difficult to place instruments directly against the subject, so it is necessary to devise ways to make clear exactly where measurements were taken. For example, if you use a stone’s corner as a representative point, you must keep consistent which corner was used, from which direction it was viewed, and at what height. Even when tracing a contour, unless you standardize which position on the edge you interpret as the line, data measured on different days will not match. In other words, improving on-site measurement accuracy involves not only the precision of the positioning equipment but also standardizing how target points are taken.

What is effective in this situation is to re-measure critical points. Rather than recording a point only once and finishing, wait a short time and measure the same point again to check whether the difference is large. This makes it easier to detect intermittent reception failures or operator errors on site. In particular, control points, corners of the survey area, points that will serve as references in later processes, and points that will be tied to photos or point clouds should be targeted for re-measurement. A few minutes of checks in the field can prevent major rework later.

Also, when taking consecutive points, it is important not to make the process too assembly-line. When capturing the outline of archaeological features or a series of stone placements in sequence, proceed while considering the necessary density and significance rather than simply increasing the number of points. Too few points will fail to express the shape, while too many will take time to organize and will obscure which points are important. In cultural property documentation, it is more practically useful to select representative points that can describe the form and to associate names or supplementary information with those points.

Coordinating with photographs is also very effective for improving reproducibility on site. If you make it possible to confirm in the photos which points or lines were measured and what they targeted, your judgments won’t waver when you organize the data later. If only positional records are taken first, it can become unclear after returning to the office what a given point was indicating. If you attach simple numbers or descriptions of the subject to the photos, the meaning of the positioning data is less likely to be lost. On sites where the shape and surface condition of the subject are important, such as cultural properties, the practice of keeping numerical and visual information together is indispensable.

Furthermore, measures are needed to reduce variability among workers. When multiple people take measurements, sharing in advance the definition of representative points, protocols for waiting during observations, criteria for re-measurement, and how to fill out record sheets will stabilize the results. In cultural heritage surveys, responsibilities may be divided among field staff, recorders, and photographers, but if records are not made in a form that anyone can read with the same meaning, later stages will become confused. High-precision position records are not achieved by excellent equipment alone; they are supported by operational rules and careful record-keeping.

In the field, it is important to refrain from forcibly adopting anomalous values. Values that clearly deviate from surrounding points, values that do not match on re-measurement, or values whose correspondence with the target is unclear should not be used as-is. When recording the positions of cultural properties, it may be impossible to return to the site, so the impulse to keep data that were obtained somehow is understandable. However, leaving dubious values will reduce the overall reliability of subsequent mapping and analysis. If necessary, re-observe on the spot, and if the results remain unstable, it is more honest as an outcome to record that conditions were poor.

What Step 3 requires is not measuring quickly, but consistently retaining meaningful points. Location records for cultural properties become the foundation for later conservation and use once coordinates are obtained. For that reason, it is important to thoroughly ensure reproducible observations, including defining target points, re-measurements, linking with photographs, and handling outliers.

Step 4: Design the organization, storage, and sharing of recorded data

Even if you can record the positions of cultural properties with high accuracy using RTK, it is meaningless if that data cannot be used later. If attention is focused only on field accuracy and the design of data organization and storage is postponed, the hard-won high-precision records will become difficult to utilize. In Step 4, we consider methods for organizing coordinate data so that it can be used as a deliverable.

First, it is important to organize point names and attribute information while memories of the site are still fresh. At cultural heritage sites, similar stones, comparable remains, and multiple photographing positions often occur close together, and as time passes it becomes difficult to judge which point indicated what. Therefore, establish a consistent naming rule for each point and record the subject type, the meaning of the location, the survey area, the date, the observer, and any notes. If naming conventions are ambiguous, it will be hard for another person to understand the records later.

Next, what is needed is linking with photos, field notes, drawings, point clouds, and so on. In cultural heritage recording, location coordinates alone rarely suffice. For example, the location of damage requires corresponding photographs, and a sequence of points outlining features must be organized in a form that can be rendered on a plan. By linking photo numbers and record numbers with coordinates, it becomes easier to verify site conditions later. When dealing with point clouds or three-dimensional models, because location records serve as a common reference axis, the care taken in attribute management has a major impact on the efficiency of subsequent processes.

Also, for records of cultural properties, a storage format that takes future reuse into account is important. To ensure readability even if personnel change, coordinate information and associated data should be retained in a form that is not overly dependent on a particular environment. Keep original data, cleaned/processed data, produced drawings, photo correspondence tables, observation notes, and the like stored separately, and make clear which files are the source data and which have been edited to prevent accidental overwriting and confusion. Because cultural properties are intended for long-term preservation, preservation planning is required that can be referenced years later, not just optimized for short-term work efficiency.

The way results are shared is also part of quality. Even if high-precision coordinates are obtained, they will not be used if they are difficult for stakeholders to read. Because different users—survey staff, conservation staff, design staff, management staff, etc.—require different forms of presentation, it is desirable to share not only a list of numerical values but also simple diagrams, location maps, and explanatory text. Especially in the field of cultural heritage, many stakeholders who are not familiar with surveying often review the results, so it is necessary to clearly show which points represent what and the level of accuracy to which they can be used.

What should not be forgotten here is to record supplementary information about accuracy. Leaving brief notes on the observation date and time, site conditions, re-measurement results, locations where reception was difficult, the status of corrections, and operational precautions, among other things, makes it easier to evaluate the data later. Because cultural heritage records are often compared over long periods, even if only the numerical values remain, it becomes difficult to judge their reliability if one cannot understand why those values were obtained. A high-quality accurate record is not about the fineness of the coordinate values, but about being able to explain the coordinates including their background.

In other words, Step 4 requires designing the "after measurement" phase. Location records of cultural heritage are not something that are completed on site. Organization, preservation, and sharing together constitute a single deliverable. By carrying out this stage carefully, the high-precision data acquired with RTK will become an asset capable of withstanding future surveys, preservation, comparison, and reuse.

Common Failures When Recording the Locations of Cultural Properties with RTK

So far we have explained four steps, but in practice certain failures tend to recur. Knowing these in advance will make on-site decision-making much more stable.

The first is starting measurements without deciding the required accuracy. If you adopt RTK simply because you vaguely want higher precision, it becomes unclear which points require what level of verification. As a result, checks on important points can be insufficient, or conversely you may spend too much time on points that are not important. When recording the positions of cultural properties, it is important not to treat everything with the same level of strictness, but to apply different levels of rigor according to the intended use.

The second is underestimating site conditions. If observations are made without considering the overhead environment and the effects of surrounding reflections, quality can vary from point to point even within the same site. In particular, in areas with many trees or near stone walls, it is dangerous to assume the readings are reliable just because numbers are produced. The worse the conditions, the more you should increase re-measurements and supplementary documentation.

Third, recording while the definition of the target point is left ambiguous. If it is not consistently defined—whether the target is the outer edge of a feature or its center, or the corner of a stone or its center—then however high the positioning accuracy, the results will be unstable. In cultural heritage recording, how the target is defined is central to quality.

The fourth mistake is collecting only coordinates and postponing organization. Because time is limited on site, people tend to just record points and deal with them later, but this approach is prone to failure. If you don't organize point names, photo correspondences, and observation notes on the spot, you'll inevitably encounter information you can't interpret once you're back at the office.

The fifth is skipping re-measurement. If you accept a value obtained once at face value, you can overlook anomalous readings or mix-ups. Because the cost of revisiting cultural properties is often high, the more important the point, the more it should be checked on site.

These failures stem less from any particular lack of technical skill than from inadequate preparation and operational design. In other words, RTK-based recording of cultural heritage locations tends to be stable when procedures are properly established and prone to instability when procedures are omitted.

Approach to Balancing Efficiency and Accuracy in Cultural Heritage Documentation

In the field of cultural heritage, pursuing accuracy alone cannot be put into practice unless it is reconciled with constraints on working time, personnel, and preservation. Conversely, prioritizing efficiency alone leads to an increase in records that will be unusable in the future. Therefore, what is important is not to set accuracy and efficiency against each other, but to determine the quality required for each object being recorded and to establish a system that can be operated smoothly without undue burden.

For example, there is an approach that carefully records the reference points and key points that form the framework of the entire site, while adjusting the density of surrounding supplementary records according to their intended use. This ensures that the foundational parts of the deliverables are reliably high-quality without making the overall work overly burdensome. Also, by thinking of photos, drawings, point clouds, and positional information as connected from the outset, you can reduce the waste of repeatedly checking the same location by different means.

Furthermore, it is important to choose equipment and procedures that anyone can use with consistent quality. At cultural heritage sites, position recording is sometimes carried out not only by specialist surveying technicians but also by investigation staff and conservation personnel. In such cases, workflows that presuppose complex operation or cumbersome post-processing are unlikely to become established. Choosing systems that are easy to use in the field, ensure the required accuracy, and can be readily linked to photographs and recorded data will ultimately lead to higher precision.

If you want to more firmly root the recording of cultural property locations in field practice, you should emphasize continuity as well as accuracy. A method that relies on a particular skilled operator each time will see quality decline when personnel change. By standardizing procedures and converting them into a form that is easy to follow on site, the reproducibility of records will improve. RTK is an effective means for that purpose, and if used in a way suited to the site, it can steadily raise the quality of cultural property records.

Summary

To improve the positional recording of cultural heritage with RTK, simply relying on high-precision positioning capabilities is not enough. It is important to clarify what you want to record and to what accuracy, develop an observation plan tailored to site conditions, record on-site using reproducible methods, and design the subsequent organization and preservation as an integrated process. By following these four steps, positional records of cultural heritage become not temporary notes but foundational information capable of withstanding future comparisons and preservation use.

Especially at cultural heritage sites, where it is difficult to touch the object, environmental conditions are not consistent, and later reconfirmation is difficult, an approach that preserves the meaning of records—not just numerical values—is indispensable. RTK greatly enhances the reliability of positional information in such fieldwork and serves as a common coordinate foundation that links photographs, drawings, point clouds, and survey records.

If you want to carry out on-site tasks such as control point surveying, verification of known points, layout of survey areas, and positioning of record photographs more efficiently with fewer personnel, LRTK, a high-precision GNSS positioning device that attaches to a smartphone, is an easy option to incorporate into practical work. Even on cultural heritage sites, it enables you to quickly obtain centimeter-level (half-inch accuracy) position information where needed, reducing rework in recording tasks and helping produce data that is easier to use in downstream processes. If you want to balance the accuracy of position records with ease of field operation, it is worth considering the use of LRTK within the workflow of cultural property surveys and preservation activities.