Top 5 Failures in RTK Point Cloud Measurement and Countermeasures｜From Multipath to Antenna Placement

Table of Contents

• Introduction

• Failure Case 1: Accuracy degradation due to multipath

• Failure Case 2: Unable to obtain a fixed solution

• Failure Case 3: Antenna installation error

• Failure Case 4: Loss of communication with the base station

• Failure Case 5: Incorrect coordinate system settings

• Pre-project preparation checks

• Preliminary checklist to prevent failures

• Anomaly detection and response flow during measurement

• PDCA cycle learned from failures

• Technical foundation supporting high-precision measurement

• Mechanism for systematically managing failure risks

Introduction

In the practical work of the surveying and construction industries, while there are high expectations for the introduction of RTK point-cloud measurement technology, encountering unexpected problems on actual job sites is not uncommon. Because it is an advanced technology, even slight configuration errors, mistakes in assessing the environment, or operational carelessness can lead to serious measurement failures.

The important thing is that, while it is difficult to completely avoid failures, learning from the mistakes of those who came before can greatly reduce their occurrence. In this article, we analyze in detail five representative failure cases that actually occurred in the field of RTK point cloud measurement and explain the causes and countermeasures for each.

By understanding these examples, awareness of potential crises at the measurement planning stage will increase, risk management during the execution stage will improve, and ultimately this will lead to achieving highly reliable measurement results. RTK point cloud surveying is an extremely useful technology when performed properly. Learning from failure cases is an important step to maximize its effectiveness.

Learning from failures and continuing to improve leads to the overall advancement of technology across the industry. We hope that the examples and countermeasures introduced in this article will help you avoid problems on-site and contribute to the success of your projects.

Failure Case 1: Accuracy Degradation Due to Multipath

Multipath is the phenomenon in which radio signals from satellites reach a receiver via multiple paths. In addition to the direct-path signal, signals reflected off nearby buildings and the ground arrive later, degrading positioning accuracy. This is one of the most common problems in RTK measurements.

An actual failure case involved measurements at a construction site in an urban area. They attempted to perform high-precision RTK point-cloud measurements in a narrow measurement area surrounded by buildings. In theory, an accuracy of several centimeters (a few in) could be expected, but the actual measurement results showed errors reaching tens of centimeters (several in to over 1 ft). Subsequent analysis revealed that multipath was occurring due to signal reflections from the walls of the surrounding reinforced concrete buildings.

A detailed analysis of the cause showed that four- to six-story buildings existed in all 360 degrees around the measurement area, and signal reflections from each direction overlapped. In addition, the ground of the measurement area was paved with concrete, and reflections from the ground were strong enough that they could not be ignored.

As a countermeasure, changing the measurement time window can be effective. Because satellite positions change over time, there may be fewer signal reflections at certain times. At this site, changing the measurement period to the morning significantly reduced the impact of reflections.

As another countermeasure, it was also considered to place the receiving antenna as far as possible from sources of reflection. By installing the antenna as high as possible, the influence of reflections from the ground could be reduced, relatively increasing the proportion of the signal traveling via the direct path.

In the long term, the adoption of receivers that support multiple satellite systems is recommended. Instead of relying on GPS alone, combining GLONASS, Galileo, and BeiDou increases the number of satellites that can be received and can statistically reduce the effects of multipath.

Failure Case 2: Unable to obtain a fixed solution

In RTK positioning, reaching a fixed solution is an essential prerequisite for achieving high accuracy. However, depending on the measurement environment, initialization to a fixed solution can be extremely difficult.

As a practical example, there was surveying for large-scale civil engineering work in a mountainous area. The construction site was located in a valley and was surrounded by mountains on all sides. Whereas the theoretical initialization wait time was on the order of tens of seconds, in practice initialization could take tens of minutes or could even fail to reach a fixed solution.

Analysis of the cause revealed that limited satellite visibility was the main reason. Mountains were causing obstructions from all directions, limiting the number of satellites that could be received simultaneously. In addition, the geometric configuration of the received satellites was poor, and the DOP values became very large.

As a first step in the countermeasures, an attempt was made to install the receiving antenna as high as possible. The tripod height was set to 3 m (9.8 ft), and by installing the receiving antenna at its top, the visibility of some satellites improved slightly and the initialization time was shortened.

As a second countermeasure, the use of multiple satellite systems was considered. Instead of GPS alone, switching to a GLONASS-compatible receiver greatly increased the number of satellites that could be received and made initialization possible. Furthermore, by introducing the latest receiver compatible with Galileo, initialization time was reduced to several seconds to around ten seconds.

In the long term, installing the reference station in a more open location was recommended. Relocating the reference station from the valley floor to a hill slightly higher than the surrounding mountains improved satellite visibility and greatly increased the reliability of obtaining fixed solutions at measurement sites.

Failure Case 3: Antenna Installation Error

The role of the receiving antenna in RTK positioning is extremely important. The antenna’s physical location, orientation, and surrounding environment are directly linked to the quality of the received signals. Installation errors may seem like a simple problem at first glance, but in reality they can cause the entire measurement to fail.

As a real-world failure example, there was repeated measurement at a construction site. When we compared the measurement results from the first session with the data from the second session one week later, the readings at the same locations differed by tens of centimeters (several to a few dozen in). The reason was unknown, and we even suspected a malfunction of the measurement system.

Detailed investigation revealed that, in the second session, the reference station antenna had been installed in a different position. As a wind countermeasure, the antenna had been moved slightly from its initial installation position. The movement distance was visually extremely small, but there were displacements on the order of several tens of centimeters (several tens of inches).

Errors in the antenna's horizontal position directly introduce errors into the coordinates of the reference point. If the reference point's coordinates are inaccurate, that error propagates throughout the entire measurement area and throws off the whole measurement.

As a countermeasure, fixing the reference station antenna position was considered. The antenna was secured to the top of the tripod, and the tripod was anchored to the ground with fixing bolts so that the antenna’s position would not move at all. In addition, the antenna’s installation position was recorded with images so it could be set in the same position for the next session.

The orientation of a GPS receiver's antenna is also important. Normally the antenna should be pointed toward the zenith, but if it is installed at a tilt, the quality of the received signal deteriorates. There is also a technique called perspective normalization (tile turn) that intentionally tilts the antenna, but installation in accordance with protocol is recommended.

Failure Case 4: Loss of communication with the reference station

In RTK positioning, high accuracy is achieved only after correction data from the base station reaches the rover. If this communication is interrupted, correction information cannot be obtained, and accuracy decreases significantly.

One real-world failure case involved surveying at a vast construction site. A reference station was installed at one corner of the site, and measurements were planned at points up to several kilometers (several mi) away from it. During the first half of the measurements we were obtaining good fixed solutions, but as the surveying progressed initialization began to fail, and ultimately the rover lost communication with the reference station.

Analysis of the cause showed that as measurements progressed, the mobile station was moving away from the reference station. The measurement area was actually larger than planned and exceeded the reference station’s radio communication range of several kilometers (a few miles). In addition, there was mountainous terrain in between that blocked the line-of-sight propagation of the radio waves.

As a countermeasure, installing multiple reference stations is effective. We divided the measurement area into several subareas and installed a dedicated reference station in each subarea, ensuring that all mobile stations could communicate with a nearby reference station.

As an alternative measure, the use of a wide-area RTK distribution service was considered. By using a service that delivers correction information via the cellular network, we were freed from the range limitations of physical radio communications. However, because using this service incurs a monthly fee, a decision needed to be made with economic viability in mind.

To improve the reliability of communications, it is also important to identify the radio frequency bands to be used and select bands with low electromagnetic interference. It is recommended to survey other wireless usage around the site in advance and avoid using frequency bands that may be subject to interference.

Failure Case 5: Incorrect Coordinate System Configuration

Errors in setting the coordinates of reference points and in defining the coordinate system are serious issues that fundamentally undermine the reliability of measurement data.

As a real-world failure case, there was progress management spanning multiple construction stages. In the second measurement, taken three months after the initial measurement, the readings at the same location were off by several meters (several ft). We even suspected a malfunction of the measuring equipment.

A detailed investigation revealed that, in the second measurement, the coordinates used as the reference point had been changed. While the first measurement referenced a national survey control point, the second used coordinates independently determined by personnel at the measurement site as the reference. The difference between those two coordinate values reached several meters.

The fundamental cause of this failure was inadequate management of the coordinate system. In projects where multiple stakeholders are involved in measurements, clear instructions and records regarding the unification of coordinate systems are critically important.

As a countermeasure, at the start of the project we clearly documented the regulations for managing coordinate systems and ensured that all stakeholders reviewed them before carrying out measurements. We described in detail the source of the coordinates used as reference points, their level of accuracy, and the definition of the coordinate system.

Confirmation of coordinate system unification across multiple sessions has also been strengthened. After measurements in each session, a verification checklist is now used to confirm whether the coordinate system matches the previous one. If a mismatch is discovered, a procedure has been established to investigate the cause and re-unify the coordinate system.

Preparation Checklist Before Project Start

Thorough preparation before starting is critically important to the success of an RTK point cloud measurement project. Systematically carrying out the following checklist items can significantly reduce the risk of failure.

During site surveys, we check the satellite visibility at the planned measurement location. We create a GNSS signal reception availability map in advance and identify areas with poor reception conditions. We evaluate obstruction by trees and buildings and, when necessary, determine adjustments to the measurement time windows and the need for receivers that support multiple satellite systems.

Preliminary investigation of survey control points is also important. Determine whether existing survey control points are available or whether new control points need to be established. If new control points are to be established, determine their positions and plan the process to determine their coordinates with high precision.

Checking the communications environment is also essential. You should determine whether you can set up a wireless communications environment to transmit correction data from the base station to the mobile station, or whether to use a wide-area RTK service.

Training of personnel is also important. Ensuring that those engaged in measurement work understand the basic principles of RTK positioning and how to respond to potential issues speeds up responses when problems occur on site.

Preliminary Checklist to Prevent Failures

What can be learned in common from the five failure cases above is the importance of thorough preparation before measurement and rigorous quality control during the execution phase. To systematically ensure these elements within an organization, the use of a pre-measurement checklist is effective.

The measurement environment checklist should include a preliminary survey of the satellite reception environment (satellite visibility, DOP values, and the possibility of multipath), selection of the reference station installation site, and verification of the communications environment.

The equipment installation checklist should include confirming the reference station antenna’s position and orientation, checking levelness, verifying tripod stability, confirming the receiver’s power supply, and checking communication connections.

A coordinate system management checklist should include checking the coordinates of reference points, confirming the definition of the coordinate system, verifying consistency with the coordinate system used in the previous measurement, and checking the completeness of the records.

During measurements, monitoring items should include confirmation that a fixed solution is maintained, monitoring the number of satellites received, monitoring DOP values, and monitoring the communication connection status.

By using these checklists systematically, most failures can be prevented in advance.

Anomaly Detection and Response Flow During Measurement

If an unexpected problem occurs during measurement, a prompt and appropriate response is required. By defining in advance the process from detecting an anomaly to responding, you can minimize confusion.

As a procedure for handling cases where a fixed solution cannot be obtained, first check the satellite reception status. Verify whether the number of satellites is insufficient and whether the DOP value has deteriorated, and make an initial assessment of whether there are problems with the reception environment. If there are no environmental issues, check communication with the reference station. If communication is normal, extend the initialization waiting time. Normally, initialization takes tens of seconds to a few minutes.

If communication with the base station is interrupted, check the communication cable and connections. If there is no problem with the connections, review the communication frequency and power settings. If the problem is not resolved, consider installing an auxiliary base station or switching to a wide-area RTK service.

If a decline in accuracy due to multipath is suspected, attempt changing the measurement time or making fine adjustments to the antenna position. If no adjustments lead to improvement, temporarily suspend measurements and plan to conduct them in a better environment.

If an anomaly in data quality is detected, temporarily suspend measurements and prioritize investigating the cause. Continuing measurements despite this may make issues in the post-processing stage more complex.

Learning the PDCA Cycle from Failures

To learn from failures as an organization and continuously improve, introducing the PDCA (Plan, Do, Check, Act) cycle is effective.

In the planning phase, we refer to past failures and incorporate preventive measures into the measurement plan to prevent similar failures from recurring.

During the implementation phase, we will carry out the plan carefully and perform real-time quality monitoring.

In the evaluation phase, after completing the measurements, the measurement process and results are reviewed and a detailed record is kept indicating whether any problems occurred or whether any unexpected issues arose.

In the improvement phase, we will refine measurement methods, checklists, training content, and other items based on the evaluation results, and incorporate them into the next measurement.

By repeating this PDCA cycle, the organization as a whole will progressively improve its level of implementation of RTK point cloud measurements.

Technical Foundation Supporting High-Precision Measurement

Many of the failure cases described so far are due more to inadequate operation and management than to technical difficulties. However, fundamentally, understanding the technical foundation that supports high-precision measurement is important.

Having basic technical knowledge—such as the fundamental principles of GNSS positioning, the concept of coordinate systems, and the flow of data processing—enhances the ability to respond to unexpected situations. For example, if you understand why a fixed solution cannot be obtained, you can quickly determine whether it is a satellite visibility issue, a communication problem, or a receiver configuration error. Regular training and the sharing of technical information contribute to improving the capabilities of the entire organization. In large-scale projects, regular knowledge sharing between technical staff and field personnel and the accumulation of best practices lead to continuous improvement.

The emergence of new tools, such as iPhone-mounted high-precision GNSS positioning devices, is bringing high-precision measurement closer to users and also facilitating simplification of their operation. However, as tools evolve, it is also necessary to deepen our understanding of their mechanisms and limitations. The more streamlined the tools become, the harder it is to see the complex processes behind them, and the greater the risk of incorrect usage. In particular, understanding the limitations of the tools—such as long initialization times and vulnerability to multipath—is essential for proper operation.

The value of introducing high-precision measurement technologies is realized only when personnel are trained to correctly understand the technologies and to operate them appropriately. A culture of continuous learning and improvement forms the foundation that supports those technologies. Sharing failure cases across the organization and extracting lessons from them significantly improves project success rates.

Mechanisms for Systematically Managing Failure Risks

To prevent failures in RTK point cloud measurements, the essential countermeasure is to build an organizational failure-risk management system rather than rely solely on individual vigilance. By recording and analyzing failure cases and sharing and applying the insights gained across the organization, recurrence of the same failures can be prevented and continuous quality improvement can be achieved.

Building a database of failure cases is the first step. Establish a database that records problems that occurred during measurements, their causes, the remedial actions taken, and future preventive measures. Regularly update it during post-project reviews so that all team members can access and refer to it.

Making root cause analysis a routine is also important. When a failure occurs, conduct analyses that dig deeply into why the failure happened, rather than relying on superficial fixes (such as why-why analysis). Once the root cause is clarified, preventive measures become more effective.

Latest high-precision positioning devices, such as LRTK (iPhone-mounted GNSS high-precision positioning device), are equipped with real-time measurement quality verification functions that contribute to the early detection of failures. By making on-site quality checks easier, the worst-case scenario—where issues are discovered only during post-processing—can be avoided. The combination of systematic failure management and advanced measurement technologies forms the foundation for continuously improving the quality and reliability of RTK point cloud measurements.