Utility Mapping with RTK: Recording Manholes, Valves, and Utility Poles

Table of Contents

• Introduction

• What is utility mapping

• What is RTK (Real Time Kinematic)

• Benefits of using RTK for utility mapping

• Accurately recording manhole locations

• Accurately recording valve (underground pipe valve) locations

• Accurately recording utility pole locations

• Field tips for RTK surveying

• Efficiency gains from new technologies

• Conclusion

• FAQ

Introduction

Infrastructure such as water and sewer pipes, power and communication cables that spread across roads and underground — accurately knowing their positions on a map is indispensable for managing and maintaining them. However, conventional maps and drawings often show manholes, valves, utility poles and the like offset from their actual positions by several meters (several ft). Many people have experienced situations like “I can’t find the manhole at the location shown on the plans” or “it took a long time to locate a pipe valve” when opening covers on site. Inaccurate utility location information lowers the efficiency of construction and inspection work and, in some cases, can lead to accidents such as accidental excavation.

Utility mapping has drawn attention as a response. This refers to accurately surveying and recording the positions of buried objects and related facilities and reflecting them on digital maps or GIS (Geographic Information System). RTK (Real Time Kinematic) has attracted significant attention as a technology that can dramatically improve the efficiency and accuracy of utility mapping. This article explains what utility mapping is and what RTK technology is, introduces the benefits of using RTK through concrete examples such as manholes, valves, and utility poles, touches on efficiency gains enabled by new field technologies and tools, and finally mentions solutions that make high-precision positioning easily achievable.

What is utility mapping

Utility mapping is the detailed and accurate mapping of the positions of various infrastructure facilities located under roads or on the ground. “Utilities” refers to public lifeline facilities such as electricity, gas, water and sewer, and communications. Examples include manholes, various valves, fire hydrants, utility poles, transformer boxes, and cable entry points. Traditionally, position information for these utilities relied on paper drawings and construction records. However, old drawings often have discrepancies with actual positions due to missed updates or surveying errors. While specialized nondestructive exploration methods (such as ground-penetrating radar) are required to grasp the exact route of buried pipes themselves, at minimum it is essential for infrastructure management to accurately identify surface-visible facilities (manhole covers, iron covers, valve boxes, the bases of poles, etc.).

The purpose of utility mapping is to accurately measure the locations of such infrastructure elements in the field and record them as digital data so they can be managed and shared easily on a geographic information system. For example, if you have accurate location data for water valves, you can quickly find and operate a valve on site in an emergency. If manhole locations are accurately known, inspection and cleaning can be performed without unnecessary excavation or exploration. Accurate location information for utility poles and posts is useful for asset ledger management and future relocation planning. In this way, utility mapping is attracting attention as a foundation for infrastructure maintainability, safety, and the realization of smart cities.

What is RTK (Real Time Kinematic)

RTK (Real Time Kinematic) is a technology that uses satellite positioning systems (GNSS) to perform real-time, centimeter-level high-precision positioning (cm level accuracy (half-inch accuracy)). Normally, GPS positioning used in smartphones and car navigation has errors of several meters (several ft). These errors are caused by atmospheric effects, satellite orbit errors, receiver accuracy, and so on. RTK, however, can improve accuracy to the order of several centimeters (cm level accuracy (half-inch accuracy)) by using a correction mechanism between a reference station (base station) and a mobile station (rover).

The basic principle of RTK positioning is that a reference station installed at a known position computes error information (satellite signal offsets) and sends that correction information to the rover via radio or the Internet, and the rover applies those corrections to compute its position. In Japan, there is an environment where high-precision positioning can be performed without installing your own dedicated reference station by utilizing the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations network and commercially provided GNSS correction services (network RTK services). More recently, technologies have appeared that use augmentation signals from Japan’s Quasi-Zenith Satellite System “Michibiki” (centimeter-class augmentation service: CLAS) to enable high-precision positioning even in mountainous areas where Internet connectivity is limited.

The advantage of RTK is that it obtains high-precision positions in real time. Because positioning results are obtained on the spot, work can proceed while confirming positions on site. Conventional GPS often required post-processing to correct errors later. RTK, on the other hand, provides accurate coordinates immediately in the field. This feature is powerful for tasks like utility mapping, which involves measuring many points in the field.

Benefits of using RTK for utility mapping

Introducing RTK positioning to utility mapping sites offers the following advantages compared with traditional methods.

• Significant improvement in positioning accuracy: Coordinates obtained with RTK are extremely accurate, with errors on the order of a few centimeters (cm level accuracy (half-inch accuracy)). Even small objects such as manholes and valves can have their exact positions recorded. This minimizes discrepancies between drawings and actual conditions and reduces the risk of excavating the wrong location.

• Improved work efficiency: With RTK, positioning at a single point can be completed in a matter of seconds. Compared with traditional methods using tape measures or total stations, surveying time is greatly reduced. Especially in urban areas where many targets must be measured (for example, dozens of manholes), RTK allows one person to survey quickly.

• Reduction of human error: Manual methods—writing positions on maps by hand or measuring distances with tape measures—are prone to recording or reading errors. Digital positioning with RTK automatically records obtained coordinates, reducing mistakes. Data can also be stored and shared electronically, preventing information loss in communication.

• Improved safety: Traditional methods that require stretching tape on roads or stepping into traffic to take measurements pose risks to workers. RTK GNSS allows measurements from a safe distance by extending the antenna, letting workers avoid standing in roadways as much as possible. Shorter measurement times also reduce the duration of on-road work.

• Immediate on-site verification: Because RTK provides high-precision coordinates on the spot, those positions can be instantly checked on maps on a mobile device. You can verify where the measured point is plotted on a map and, if there is an anomaly, remeasure immediately. This feedback would not have been available if data were processed afterward.

With these benefits, RTK makes utility mapping accurate and speedy, improving infrastructure management quality. Next, let’s look at what can be recorded with RTK for specific objects and key points to keep in mind.

Accurately recording manhole locations

Manholes are access points to underground facilities such as sewers or shared conduits for power lines, typically seen as circular or rectangular covers on road surfaces. Accurately recording manhole locations is crucial for managing sewer routes, planning dredging work, and recovery activities in disasters. Using RTK, you can measure and record the center point of a manhole cover to the centimeter (cm level accuracy (half-inch accuracy)).

Measurement tips: For metal covers, satellite signals may be disturbed when the GNSS antenna is positioned directly above the cover. When placing the tip of an RTK pole (surveying pole) on the center of the cover, pay attention to the cover material and radio conditions affected by surrounding buildings. Taking a few seconds of measurement and averaging the results as needed can yield a stable position. Because manhole covers are large in diameter, taking an accurate center requires careful visual alignment of the pole to the cover center. It is reassuring to take multiple measurements and compare results to check for obvious discrepancies.

Using recorded data: Coordinates obtained by RTK can be imported into a GIS and plotted on a map. If each manhole is linked with attribute information such as ID, depth, and pipe diameter, it can be centrally managed as a digital ledger. This allows intuitive understanding from the map of questions like “Where is the next cleaning location?” or “Which manholes are deteriorating?” With accurate location data, future applications such as highlighting manhole locations on-site through AR (augmented reality) via a smartphone are conceivable.

Accurately recording valve (underground pipe valve) locations

Valves are shut-off devices that control fluids in water or gas pipes and are provided with small covers or boxes on the road surface for above-ground operation. In emergencies, quickly identifying valve locations to shut off water or isolate gas is essential. Valve covers are small and inconspicuous and can blend into asphalt, making them easy to miss. By surveying all valve locations with RTK in advance and preparing an accurate coordinate list, you can respond precisely on site during emergencies.

Measurement tips: Valve covers are typically round or square iron covers with diameters of several tens of centimeters; they are nearly flush with the road surface. When measuring, place the tip of the RTK pole at the center of the cover and keep it vertical while positioning. As with manholes, watch for satellite signal disruption caused by metal covers and measure when satellite reception conditions are good. If the cover is warped or buried in debris and you cannot place the pole at the center, you can place the pole on the cover edge and later compute a correction to the cover center (though if on-site immediacy is important, it is more efficient to aim for the center as much as possible).

Using recorded data: Valve location data obtained by RTK are powerful when integrated into pipeline management GIS. If each valve is linked to an identifier and pipe type (potable water, gas, etc.), simulations such as “which valve should be closed to stop water to this section” become easy on the map. Precise coordinates make it possible to locate valves in the field using GPS even during snow cover or at night. Combined with periodic inspection records, you can spatially manage information such as when each valve was operated and how much force was required to open/close it (stiffness).

Accurately recording utility pole locations

Although utility poles (including telephone poles and streetlight poles) are highly visible, their exact coordinates are often not precisely known. Power companies and communications providers manage pole locations internally, but municipal road ledger maps and open geospatial data may simplify them. Accurate pole location information helps, for example, to precisely identify poles that need to be relocated in road widening projects or to quickly locate poles that collapsed in a disaster for recovery planning.

Measurement tips: For poles, it is physically possible to place the antenna directly at the base, but if nearby buildings or trees block the sky view, positioning may be unstable. It is often better to tilt the pole from the side with better visibility and align the tip with the pole base before pressing the measurement button. Some modern RTK receivers have built-in tilt sensors that can correct the tip position coordinates even when the pole is tilted. Using such functions allows you to obtain the base coordinates from positions less obstructed by overhead wires. Note the pole number (the plate number attached to the pole) during measurement, as this helps when organizing data later.

Using recorded data: Pole coordinate data can be integrated with other utility facility data for comprehensive urban infrastructure management. Attributes such as pole height, material, and installation year are also managed, but with accurate position data, analyses like automatically calculating clearance distances to other buried utilities on a GIS become possible. Publishing pole positions on maps for residents can be used for regional disaster prevention maps and landscape simulations (e.g., identifying which poles to underground to improve scenery). High-precision data obtained with RTK provide value across a wide range of applications.

Field tips for RTK surveying

Here are some points to keep in mind to carry out RTK-based utility mapping smoothly.

• Ensure sky visibility: RTK requires receiving signals from satellites overhead, so accuracy is more stable in open-sky locations. In areas with tall buildings or dense trees, satellite visibility can be blocked and positioning may become unstable. In such environments, choose measurement times when satellite geometry is favorable (when more satellites are visible), or measure from directions that are less shaded by buildings.

• Confirm positioning mode: Check the RTK receiver or GNSS terminal display and make sure it shows a “Fix” solution (not a float solution) before recording positioning data. A Fix solution means RTK corrections are stably applied and a high-precision solution (the computed coordinates) is obtained. If you record while in a float solution, accuracy is degraded; it is better to wait until a Fix is achieved.

• Antenna height and instrument corrections: When using a pole or monopod, correctly enter the GNSS antenna height (distance from the ground to the antenna). Incorrect antenna height input shifts the obtained coordinate heights. When measuring with the tip off the ground (e.g., measuring a pole base with the pole tilted), use tilt sensors or software offset functions to correct the tip position coordinates.

• Back up measurement data: Get into the habit of saving field measurements not only on the device but also regularly to the cloud or other media, so that important positioning data are not lost if the device fails or is lost. Many modern surveying apps provide cloud integration and can automatically sync field points.

• Battery management: RTK surveying uses GNSS receivers and communication devices (mobile routers, smartphones, etc.), so be mindful of battery depletion during long tasks. Prepare spare batteries or mobile chargers and recharge during breaks to avoid loss of power at critical moments.

Efficiency gains from new technologies

In recent years, advances in RTK positioning technology and digital tools have further improved the efficiency of utility mapping sites. New positioning devices and apps that integrate with smartphones and tablets have attracted attention.

For example, a system combining a dedicated high-precision GNSS antenna with a smartphone makes it possible to go to the field with much more compact equipment than conventional surveying instruments. An app on the smartphone can display maps and drawings while plotting RTK-measured points in real time. This eliminates the need to carry paper drawings, and measured data can be uploaded to the cloud and shared on site.

Integration with AR (augmented reality) technology is also progressing. Visualizing previously surveyed and recorded utility positions through a smart device’s camera makes attempts to “make invisible underground utilities visible.” Demos exist in which embedded pipe routes or valve positions are displayed on the screen when a smartphone is held up. Because RTK provides high-precision position data, AR displays can be reliable and closely aligned with actual objects.

Thus, the fusion of RTK and ICT technologies is evolving utility mapping. Beyond labor savings on site, immediate data sharing and visualization improve shared understanding among stakeholders, producing wide-ranging effects as part of digital transformation (DX).

Conclusion

By applying RTK technology to utility mapping, it has become possible to record infrastructure positions with unprecedented accuracy and leverage that for management. Accurate positioning of manholes, valves, and utility poles directly improves field work efficiency and safety. In a country like Japan, where underground infrastructure is highly developed, such high-precision spatial information foundations are essential for disaster prevention and aging infrastructure countermeasures.

Solutions that make RTK surveying more accessible are now available. For example, using systems like LRTK enables centimeter-level positioning with a smartphone in hand even for non-expert users. LRTK is a platform that combines a high-performance GNSS receiver with a mobile app and is designed to achieve stable positioning even in locations where Internet access is difficult by utilizing Japan’s “Michibiki” satellites. It is user-friendly for first-time RTK users and includes functions to save photos and notes together with recorded points and share them on the cloud.

Improving accuracy and efficiency in utility mapping will only grow in importance. Why not promote DX in infrastructure management by leveraging high-precision RTK positioning and the latest supporting tools?

FAQ

Q: How accurate can RTK positioning be? A: Properly operated RTK GNSS can achieve planar positioning errors within a few centimeters (cm level accuracy (half-inch accuracy)), and in some cases less than a few centimeters (in the 10 mm (0.39 in) range). This is orders of magnitude more precise than standalone GPS positioning (errors of several meters (several ft)). However, accuracy depends on satellite reception conditions and the quality of correction information, so recognize that under ideal conditions you can expect accuracy on the order of a few centimeters.

Q: Can smartphone GPS substitute for RTK? A: Ordinary smartphone internal GPS (GNSS) can obtain positions, but their accuracy is at best on the order of several meters (several ft). This is insufficient for the sub-decimeter accuracy required for utility mapping. RTK achieves high precision through dedicated positioning mechanisms and correction information. Recently, RTK receivers that can pair with smartphones have appeared, allowing you to operate via the phone while using RTK accuracy. In other words, a smartphone alone is limited in accuracy, but combining it with RTK-capable devices yields results beyond what the phone alone can do.

Q: What is needed to start RTK surveying? A: Fundamentally, RTK positioning requires a high-precision GNSS receiver (rover) and a means of receiving correction information. Correction information is received from a reference station radio or via network distribution services (for example, commercial RTK correction services or data distribution from constantly operating reference stations). Recently, small RTK receivers that connect to smartphones or tablets have become widespread to lower the initial investment barrier. For example, systems like LRTK allow you to start full-fledged RTK surveying simply by pairing an antenna/receiver with a smartphone. Also prepare an app to confirm and save results in the field and a communication environment (mobile data, etc.) to receive correction information.

Q: Can RTK be used in areas where the sky is hard to see, such as downtown with tall buildings? A: In dense urban areas with tall buildings, satellite signals can be blocked or reflected by buildings, causing RTK to be unstable. In places with no sky view at all (such as inside tunnels), GNSS positioning is difficult. However, in partially open environments, multi-GNSS receivers can capture more satellites and mitigate accuracy degradation. Urban areas also often have good mobile coverage, making it easier to use network RTK correction data. In the field, choose points with the best sky view possible and, if necessary, measure using satellites visible from a canyon between buildings.

Q: Can RTK be used in mountainous areas without cellular coverage? A: In mountainous areas or remote islands without mobile coverage, network RTK correction data cannot be obtained. There are several solutions. One is to set up your own portable reference station and transmit correction data by radio. Another option, limited to Japan, is to use the Quasi-Zenith Satellite “Michibiki” centimeter-class augmentation service (CLAS). With a compatible receiver, you can perform RTK positioning using Michibiki signals without an Internet connection. Systems that support CLAS, such as some LRTK devices, are commercially available. With such options, utility mapping in mountainous areas can be carried out without issue.

Q: Is specialized knowledge required to operate RTK? A: Traditional surveying instruments and GNSS receivers required specialized settings and operation, but user-friendly products have increased in recent years. While basic surveying and GNSS knowledge is beneficial, systems like LRTK provide intuitive smartphone apps that guide users to obtain positioning results. Connection to a reference station and acquisition of correction data are often automated, so complex procedures are minimized. Still, understanding basics such as creating an environment suitable for satellite reception and instrument calibration will improve results. With practice, RTK can be handled adequately even by non-surveying specialists.