High-precision positioning with just a smartphone! New technology for use in architectural and civil engineering design

Introduction

In recent years, the keyword "high-precision positioning" has been attracting attention at architectural and civil engineering design sites. It has become possible to achieve centimeter-level positioning with only a smartphone, and surveying and site management methods are undergoing major changes. Until now, surveying required expensive dedicated equipment and specialist technicians, but with the advent of new technologies the era in which anyone can easily obtain precise location information is approaching. This article explains, in an easy-to-understand way while including technical details, the basics of high-precision positioning, the background that made it possible with smartphones, and the benefits of applying it in the architectural and civil engineering design fields. Using examples of challenges faced by field engineers, we introduce the solutions provided by smartphone high-precision positioning and key points for its implementation.

What is high-precision positioning?

High-precision positioning is a technology that measures positions with far smaller errors than ordinary GPS positioning. The typical GPS accuracy of consumer smartphones is said to be on the order of a few meters, but high-precision positioning can achieve errors within a few centimeters (within a few in) — an entirely different order of magnitude. This enables the strict alignment and measurements required on building and civil engineering design and construction sites.

A representative method for achieving high-precision positioning is RTK (Real-Time Kinematic). RTK corrects errors by relative positioning to a reference receiver and performs centimeter-level positioning in real time. Traditionally, RTK positioning required a set consisting of a surveying GNSS receiver and a rover plus radio communication devices. It was common to realize RTK by using the Geospatial Information Authority's CORS network or private correction data services, incurring high equipment and operating costs. However, recent technological advances have made these high-precision positioning methods smaller and lower-cost, allowing them to be handled by more accessible devices.

On construction and civil engineering sites, it is necessary to measure positions with millimeter-level precision (millimeter-level precision (0.04 in accuracy)) in order to place structures according to design drawings. For example, when installing a building foundation in the correct position or burying pipes and cables along specified coordinates in infrastructure works, the several-meter errors of ordinary GPS are insufficient. High-precision positioning is powerful in these situations and enables layout and measurements with accuracy comparable to optical surveying instruments such as total stations.

Background that made high-precision positioning possible with smartphones

The reason smartphones can be used for high-precision positioning is the evolution of hardware, software, and communication environments.

• Hardware evolution: Modern smartphones are equipped with high-performance GNSS receivers that can receive multiple satellite systems simultaneously, including GPS, GLONASS, Galileo, and Michibiki (QZSS). Furthermore, some of the latest smartphones support dual-frequency reception such as L1 and L5, reducing atmospheric errors and improving accuracy. In addition, some smartphones, including iPhones, incorporate small LiDAR sensors (laser-based rangefinders), enabling the capture of surrounding 3D shapes. This advanced set of sensors makes high-precision positioning possible on small devices.

• Software evolution: Advances in smartphone OSes and applications are also indispensable. On Android, mechanisms have been developed to access raw GNSS measurement data, allowing developers to implement positioning algorithms. In addition, apps and cloud services for dedicated devices that pair with smartphones have emerged, enabling real-time correction and analysis of positioning data. For example, differential corrections can be applied to obtained satellite data to immediately compute high-precision positions, or point cloud models can be generated in the cloud from captured images — software support has dramatically improved the accuracy and practicality of smartphone positioning. The development of AR (augmented reality) technologies and 3D scanning has also supported new forms of field operations using smartphones.

• Advances in communication environments: High-precision positioning requires the exchange of correction information, and smartphones’ constant internet connectivity is advantageous in this respect. Through mobile networks and Wi‑Fi, GNSS correction data provided by government or private services (such as RTK base station information or SBAS signals) can be received in real time. In Japan, the quasi-zenith satellite "Michibiki" provides a centimeter-level augmentation service (CLAS) (centimeter-level (half-inch-level)), and with compatible receivers, smartphones can perform high-precision positioning over wide areas. Cloud integration also allows positioning results and 3D scan data to be shared and stored instantly. The spread of high-speed communications such as 5G has made large-volume data transmission smoother, creating a foundation for instantaneous information exchange between the field and the office.

As described above, the trio of device performance, software, and communication infrastructure has come together to make the new technology of "high-precision positioning with a smartphone" a reality. Surveying and measurement that once required dedicated equipment costing several million yen can increasingly be performed with a smartphone in your pocket.

Challenges in architectural and civil engineering design and the need for high-precision positioning

Accurate on-site measurement data are always required throughout the architectural and civil engineering design and construction process. However, the field has faced the following challenges.

• Burden of surveying work: Traditionally, layout setting and as-built management required requesting a surveying specialist team or an external surveying company, which consumed time and cost. Site personnel sometimes had their work interrupted while waiting for survey results, causing inefficiency. Handling specialized equipment (GPS surveying instruments, total stations, etc.) requires skill, and on small teams the equipment may not be fully utilized.

• Labor shortage and skill transfer: The construction industry suffers from chronic labor shortages, and the aging and lack of skilled surveyors is a problem. With limited progress in passing skills to younger workers, there is a strong demand for surveying technology that "can be used even by non-veterans."

• Adapting to digitalization: Initiatives such as *i-Construction* promoted by the Ministry of Land, Infrastructure, Transport and Tourism are accelerating the trend of utilizing digital data consistently from design and construction through maintenance. While 3D surveying to acquire point cloud data of terrain and the use of BIM/CIM are recommended, traditional approaches have barriers such as "you must introduce an expensive 3D laser scanner" and "analysis takes time and results cannot be checked on site immediately." To advance on-site DX (digital transformation), more accessible means of 3D surveying and data sharing are needed.

• Surveying accuracy and reliability: Surveying accuracy is paramount to prevent design and construction errors, and equipment or methods that cannot guarantee accuracy are not trusted on site. There are natural concerns about new technologies such as "Can this method position as accurately as the drawings require?" and "Can it be used for official inspections?" For deliverables like as-built management, conformity to government-defined standards (accuracy grades) may be required, so even when adopting new positioning technologies, compatibility with current standards is a concern.

Against these challenges, smartphone high-precision positioning can become a solution that matches field needs. If a portable, inexpensive smartphone can be used by anyone to perform surveying when needed, previous bottlenecks can be eliminated. Now, let’s look at concrete examples of what can be achieved with smartphone × high-precision positioning.

What can smartphone × high-precision positioning solve?

The combination of smartphones and high-precision positioning technology can be expected to bring the following improvements and benefits on construction and civil engineering sites.

• Labor savings and speed-up: Surveying can be carried out quickly by a small team. There is no need to call a surveying crew and wait while heavy machinery or materials are idle; site personnel themselves can complete measurements in a short time. This leads to shortened construction schedules and simplified personnel arrangements.

• Real-time data utilization: High-precision position and shape data measured can be checked and shared on-site, allowing immediate verification against design drawings and as-built checks. If an error is detected, it can be corrected on the spot, helping to detect rework and mistakes early.

• Cost reduction: Rental fees for specialist equipment and the frequency of outsourced surveys can be reduced. By enabling frequent in-house "small surveys" with smartphones, total costs can be lowered and opportunity losses prevented.

• Improved safety: Measurement work in dangerous locations can change. Surveys that traditionally required two or more people at heights or beside roadways can be guided remotely or completed quickly, improving worker safety. Displaying buried utilities in AR before excavation enhances prevention of accidental damage and safety checks.

• Thorough quality control and record-keeping: Survey data-based records can be automatically saved to the cloud, building a history. It becomes possible to trace "which point was measured how," streamlining quality control and report preparation. Digital records replace paper field notebooks, making information sharing and verification easier.

In this way, smartphone high-precision positioning has the potential to positively impact efficiency, cost, safety, and quality. Next, let’s look at typical use cases showing how this technology can be used on site.

Use cases of smartphone high-precision positioning

• Visualizing design data with AR: With a smartphone that has been positioned with high precision, 3D design models of buildings and structures can be displayed on the site landscape in AR. Because alignment can be accurate to within a few centimeters (within a few in), for example, when you hold up the smartphone before construction you can overlay the finished structure at actual scale. Conventional AR suffered from position drift and the need for marker placement, but accurate positioning eliminates the need for markers and projects models precisely. This facilitates intuitive sharing of design intent and consensus-building and is powerful for reviewing construction plans.

• 3D measurement via point cloud scanning: Using the smartphone camera or LiDAR, the surrounding environment can be scanned to acquire high-precision 3D point cloud data. Since all acquired points are assigned real-world coordinates, the scanned data can be handled directly in the drawing coordinate system. Standalone smartphone scanning used to produce positional drift and distortion, but by constantly knowing a high-precision self-position, point clouds remain consistent even when walking over wide areas. In as-built management, this allows recording post-construction terrain and structures as accurate 3D data, useful for volume calculations and cross-section generation. Using a high-resolution photogrammetry mode can capture distant objects and fine cracks, enabling precise model creation for inspection records on site.

• Efficiency of pile-driving and layout marking: Smartphone positioning is useful for pile-driving and layout marking operations for foundations and structure placement. Normally, surveying instruments were needed to bring design coordinates onto the site, but a high-precision smartphone can guide workers to the specified point with navigation functions. Target direction and distance can be displayed on the smartphone screen, so workers can simply move accordingly to reach the designated location. Alternatively, AR can virtually display a ground marker indicating "mark here." This enables efficient single-person layout marking, reducing the need for multiple-person survey point operations.

• Applications to infrastructure inspection and maintenance management: Smartphones positioned with high precision are also effective for regular inspections of bridges, tunnels, and other infrastructure. Using coordinates of crack locations recorded in previous inspections, a smartphone can guide you to exactly the same spot during the next inspection. Moreover, by reproducing the previous camera position and angle via AR overlays, anyone can take current photos from the same perspective. This enables accurate comparison of changes over time and simplifies fixed-point observation. For buried pipes and cable management, storing coordinates of buried utilities allows AR previewing of buried locations during inspections, so exact locations can be known before excavation. These applications improve accuracy, efficiency, and safety in maintenance operations.

Hurdles to introduction and how to overcome them

While smartphone high-precision positioning offers many benefits, several hurdles are anticipated when introducing it on site. Below are the main issues and solutions.

• Dealing with radio environment: High-precision GNSS requires sufficient satellite reception, so accuracy can be hard to achieve in environments without a clear view of the sky. In urban areas surrounded by tall buildings, valleys in mountainous areas, or inside tunnels, satellite signal reception can be unstable. Countermeasures include securing a spot near the measurement point with as much sky visibility as possible, measuring at times when satellite geometry is favorable, or using an external antenna to raise the antenna height. Choosing multi-GNSS and dual-frequency compatible equipment also helps maintain relative positioning accuracy even in obstructed environments.

• Concerns about regulations and accuracy: When using a new positioning method for official measurements, questions such as "Do data obtained by this method meet the standards?" naturally arise. For example, deliverables for as-built management must conform to the accuracy categories set by the Ministry of Land, Infrastructure, Transport and Tourism, so verification is essential when using smartphone positioning. As a measure, initially verify smartphone positioning accuracy at known points (points whose coordinates are strictly known in advance) to understand error tendencies. If necessary, combine verification by conventional instruments and cross-check results to apply corrections in operation. Governments and research institutions are currently conducting accuracy verifications and preparing usage guidelines for new technologies, and in the future these methods may be officially recognized as surveying techniques. While monitoring the latest trends, expand the scope of application step by step through internal rules and discussions with clients.

• Operational considerations: Even if the technology is useful, it is meaningless if it cannot be used effectively on site. A situation where smartphone high-precision positioning is introduced but personnel revert to traditional methods due to unfamiliarity must be avoided. Therefore, training and support are important. At introduction, utilize workshops and on-site demonstrations by manufacturers or dealers so field staff can gain confidence through training. Prepare operation manuals and help desks to support initial uncertainty. Choosing apps with intuitive UIs also speeds up mastery. Once accustomed, users can operate the system as an extension of everyday smartphone use, so lowering the "initial hurdle" is key.

Steps for on-site introduction

To embed smartphone high-precision positioning on site, planned introduction and rollout are important. Below are general steps for designers and field engineers to smoothly adopt the new technology.

• Information gathering and trial introduction: First, gather information on what smartphone high-precision positioning systems are on the market. Investigate technical specifications, compatible smartphone models, and case studies to narrow down products that fit your use. If possible, obtain demo units or trial versions and test them on real sites. This is the stage to introduce the technology in small projects or internal experiments to verify performance and usability.

• Effect evaluation and internal sharing: Based on trial results, evaluate the new technology quantitatively and qualitatively. For example, report how much surveying time was reduced compared to before, whether the acquired data meet standards, and how site staff reacted. Share results with internal stakeholders (design, construction management, management) and discuss benefits and challenges. Collect candid opinions from field personnel, conduct additional verification if needed, and proceed in a way everyone understands and agrees with.

• Phased full implementation: Once internal agreement is obtained, start full-scale introduction on site. Initially operate with a limited team or work type to accumulate know-how. As more experienced users become proficient, expand to other projects and branches. Share success stories within the company to foster motivation to try the technology. Simultaneously prepare internal manuals and formalize operating rules to ensure organizational use rather than reliance on individuals.

• Establishment and feedback: After introduction, regularly collect feedback from the field and reflect it in software updates and operational improvements. Share new functions and usage ideas in internal study sessions to achieve further efficiency gains. Technology adoption may take time, but accumulating successful experiences will gradually gain field trust. Ultimately, aim to cultivate a culture where "measuring with a smartphone is the norm" so anyone can use it when needed.

Introduction of simple surveying with LRTK

One concrete solution for achieving high-precision positioning with only a smartphone is LRTK. LRTK is a system developed by a startup originating from Tokyo Institute of Technology; by attaching a small RTK-GNSS receiver to a smartphone and using a dedicated app, it is designed so that anyone can perform centimeter-class positioning and 3D measurement with a single device. By attaching a device weighing only about 100-odd grams to a smartphone, correction signals from multiple GNSS including quasi-zenith satellites can be obtained, and in about several tens of seconds the positioning accuracy improves to a few centimeters (a few in). In that state, the smartphone’s camera or LiDAR can be integrated to provide functions ranging from point coordinate measurement and point cloud scanning to AR model projection and pile-driving navigation, offering a variety of capabilities on site.

For example, using LRTK can complete as-built measurements that previously required specialist equipment with just a smartphone, and the acquired point cloud data can be shared to the cloud immediately. Because it is based on high-precision self-positioning, data does not distort even when walking during scanning. Also, since 3D models can be accurately displayed in AR on measured positions, discrepancies between drawings and the site can be discovered instantly. The system is designed to be usable without special skills, so even non-surveying specialists can use it in daily work — a major advantage.

To accelerate on-site DX, introducing such an all-in-one surveying tool is an effective option. Not limited to LRTK, smartphone high-precision positioning systems in general require relatively small initial investments and can leverage existing smartphones, making introduction barriers lower. It is recommended to first try it on a small site, experience the effects, and then proceed to full-scale introduction. By proactively adopting cutting-edge technologies, architectural and civil engineering sites can achieve both improved productivity and quality assurance. The new technology of high-precision positioning realized with only a smartphone may greatly transform future field operations and become a standard tool everyone can use. Please take this opportunity to experience the world of smartphone high-precision positioning.