Pro smartphones are not necessary! The new normal of high-precision surveying changed by LRTK

Recently, the use of smartphones has been attracting attention in the field of construction surveying. Among them, high-performance Pro smartphones have raised expectations that “maybe surveying can be done with this one device?” thanks to their built-in LiDAR sensors and high-precision cameras. We often hear the question, “Is an iPhone Pro necessary for surveying?” However, to conclude: high-precision surveying is possible even without the latest Pro smartphones. In fact, by using a technology called LRTK, you can achieve centimeter-level positioning (cm level accuracy (half-inch accuracy)) with a handheld smartphone. This article explains in detail the relationship between Pro smartphones and surveying, the limitations of using only a smartphone, and the new normal of high-precision surveying enabled by LRTK.

Table of contents

• Why Pro smartphones attract attention for surveying

• Limits of using Pro smartphones for surveying

• Smartphone high-precision positioning enabled by RTK technology

• What is LRTK?

• Main functions realized by smartphone + LRTK

• Benefits of introducing smartphone surveying

• Summary: the new normal of high-precision surveying

• FAQ

Why Pro smartphones attract attention for surveying

As smartphone performance has improved, there has been a growing movement in recent years to utilize smartphones for surveying at construction sites. High-end models such as the iPhone—so-called Pro smartphones—are equipped with high-performance cameras and sensors, and models equipped with LiDAR sensors in particular have attracted significant attention. LiDAR is a technology that measures the distance to objects using infrared lasers, and it has been included in iPhone models since the iPhone 12 Pro. The fact that LiDAR enables a smartphone alone to scan the surrounding environment as 3D point cloud data is revolutionary. In practice, apps using iPhone or iPad LiDAR have appeared for room dimension measurement and simple 3D scans of land, making “surveying by anyone with a smartphone” increasingly accessible.

Pro smartphones also excel in processing power and communication performance, making them suitable for workflows where data is captured, processed, and shared on-site immediately. For example, for small-area measurements of land or for checking elevation differences, it is sometimes possible to get results quickly using a smartphone app without dedicated equipment. Being able to measure with just a smartphone on hand, without bringing expensive surveying instruments, can greatly reduce effort. For these reasons, expectations have grown that “if you have a high-performance Pro smartphone, you might be able to handle surveying tasks sufficiently.”

Limits of using Pro smartphones for surveying

However, there are several limits to using current smartphones (even Pro models) alone for surveying. First is the accuracy of the GPS built into smartphones. Typical smartphone GPS error is said to be on the order of a few meters, which is fine for showing your location in a map app but does not meet the accuracy required for civil engineering surveying. Although the latest smartphones have improved accuracy through signals from Japan’s quasi-zenith satellites “Michibiki” and multi-frequency GPS reception, errors of several tens of centimeters to about 1 m (3.3 ft) can still occur. Such errors are insufficient for accurate boundary measurement of land or for positioning of structures.

Smartphone LiDAR scans also have constraints. While effective for short-range 3D scanning, point cloud data obtained by LiDAR is recorded in the smartphone device’s local coordinates, so it does not directly match map coordinates (survey reference coordinates). In other words, point cloud models acquired by a smartphone alone are relative measurements and lack absolute coordinate information indicating “where on the site” they are located. Therefore, creating survey maps of wide land areas or overlaying with other survey data requires separate georeferencing of the smartphone’s point cloud.

Moreover, the effective range of smartphone LiDAR is limited to a few meters, making it unsuitable for wide-area terrain surveying. LiDAR, as an infrared sensor, can also experience degraded accuracy under strong sunlight. In addition, using point clouds acquired with a smartphone as formal survey deliverables depends on the skill of the operator and post-processing, making it difficult to maintain stable accuracy. In practice, calculating area or volume from iPhone LiDAR point clouds involves unavoidable errors to some degree, so it is not suitable for situations requiring strict precision control.

The decisive issue is absolute accuracy. For example, land boundary surveying or construction as-built control for infrastructure may require strict standards within a few centimeters in a national coordinate system. It has been difficult for a smartphone alone to meet such accuracy requirements. In short, no matter how high-performance a Pro smartphone is, there are limits when “professional surveying equipment–level accuracy” is demanded. Unless this issue is solved, smartphone surveying could assist on-site tasks but would not be considered a fully reliable surveying method.

Smartphone high-precision positioning enabled by RTK technology

The technology that solves these smartphone surveying issues is the use of RTK technology. RTK (Real Time Kinematic) is a method that dramatically improves positioning accuracy by correcting satellite positioning errors in real time. While standalone GPS positioning typically has errors of several meters, RTK uses correction information sent from a reference station to reduce positioning errors to the centimeter level (cm level accuracy (half-inch accuracy)). RTK-capable GNSS receivers have long been used in surveying, but traditionally they required fixed base stations, large antennas, and dedicated equipment, and the hardware was very expensive.

Recently, external GNSS receivers that miniaturize this RTK mechanism and allow collaboration with smartphones have appeared. By simply connecting via a smartphone port or Bluetooth, a smartphone can utilize RTK-based high-precision positioning. If the smartphone is connected to the Internet and receives data from the Geospatial Information Authority of Japan’s reference stations (GNSS reference stations) or private correction information services (such as Ntrip), it can calculate a continuously high-precision current position even while moving. In Japan, receivers that support the quasi-zenith satellite system’s CLAS (centimeter-level positioning augmentation service) can also receive correction signals directly from satellites. When an RTK receiver is combined with a smartphone for positioning, it is possible to obtain a high-precision solution called a “Fix solution” within tens of seconds to a few minutes, achieving surveying instrument–level accuracy with horizontal and vertical errors within a few centimeters.

Thanks to RTK technology, it is not an exaggeration to say that smartphones have acquired accuracy comparable to professional surveying equipment. Centimeter-precision positioning, once available only to specialists, is becoming accessible to anyone with a smartphone. The emergence of RTK-compatible devices has dispelled concerns about smartphone accuracy and evolved smartphone surveying into a new solution capable of meeting practical demands.

What is LRTK?

LRTK is a compact high-precision GNSS receiver developed to make RTK positioning easy to use with smartphones. Developed by a startup originating from Tokyo Institute of Technology, it is sometimes described as a “pocket-sized all-purpose surveying device.” The LRTK device is attached to and connected with a smartphone to upgrade the smartphone to support high-precision positioning. It contains a high-performance GNSS antenna and receiver engine as well as a battery, packing surveying-device functionality into a compact handheld housing.

Traditionally, RTK positioning required antennas, radio equipment, and base stations mounted on tripods, involving complex preparation, but with LRTK you simply attach it to the smartphone. Since the connection is wireless via Bluetooth or the like, there is no need to connect cables between the smartphone and the device. LRTK supports Japan’s CLAS satellite augmentation signals, enabling maintenance of centimeter-level positioning (cm level accuracy (half-inch accuracy)) directly from satellites even in mountainous areas or at sites outside mobile communication coverage. Of course, correction services via mobile networks such as Ntrip can also be used.

In short, LRTK is an “RTK positioning attachment for smartphones.” Using it, your everyday smartphone transforms into a high-precision GNSS surveying instrument. Since you can achieve nearly equivalent accuracy with your existing smartphone plus LRTK without purchasing costly dedicated surveying equipment, the cost advantage is significant. The name LRTK succinctly expresses the concept of “RTK for smartphones,” and the emergence of this device has realized a new surveying style that does not even require a Pro smartphone.

Main functions realized by smartphone + LRTK

So, what exactly can you do by combining an LRTK with a smartphone? Surveying tasks that previously required specialized equipment or skilled technicians can now be achieved with smartphone + LRTK as follows.

• High-precision coordinate measurement: Using a smartphone and LRTK, you can measure the latitude, longitude, and elevation of any point with centimeter-level precision. By touching the device to a point on the ground or a structure and pressing a button on the smartphone, you can record that point’s 3D coordinates. The obtained coordinate data are automatically converted into the designated survey coordinate system (such as plane rectangular coordinates), eliminating the need for manual coordinate conversion as before.

• 3D point cloud scanning (use of surveying LiDAR): By leveraging the smartphone’s built-in LiDAR scanner or camera, you can scan the surroundings as 3D point cloud data. Performing scans while using the continuously corrected high-precision position information from LRTK means each acquired point cloud is assigned absolute coordinates based on a global reference frame. For example, you can scan terrain such as embankments or excavation areas on-site with a smartphone and immediately compute volumes. Obtaining high-precision, geo-referenced point clouds with only a smartphone and a small device is a major advantage for fieldwork.

• AR-based staking out and design verification: The smartphone + LRTK combination is powerful for construction support using AR (augmented reality). You can overlay design drawings or positions from 3D models onto the real world through the smartphone screen to perform staking out tasks or as-built checks. With a smartphone that has high-precision coordinates, design models can be projected to match the real space accurately, allowing precise marking without positional drift. Tasks that previously required two people using a transit can now be performed intuitively with a single smartphone. AR can also be used to overlay design models and existing structures to check for interferences before construction.

• Photogrammetry and record creation: Photos taken with the smartphone camera can be automatically tagged with high-precision location information. For example, when photographing locations required for as-built control, the photo data will record the exact coordinates and timestamps. When reviewing photos later, you can immediately tell where each photo was taken, making report creation and mapping on drawings easy. Some surveying apps automatically generate forms from captured photos and point data, aiding efficient site documentation.

• Cloud sharing and remote monitoring: Survey data obtained with smartphone + LRTK (coordinates, point clouds, etc.) can be uploaded to the cloud on site for sharing. Office PCs can instantly view on-site measurements, and remote stakeholders can share the data in real time. A cloud viewer can overlay point cloud data with design data for checking, enabling digital information exchange between site and office. Such data integration enables rapid decision-making and consensus-building that was difficult with paper-based workflows.

Benefits of introducing smartphone surveying

The new surveying method using smartphone + LRTK brings significant benefits to construction sites. Here are the main advantages.

• Improved work efficiency and productivity: The biggest advantage of smartphone surveying is efficiency through labor savings. Survey tasks that previously required two people can now be completed by one person, greatly reducing surveying time. For example, a site supervisor can quickly measure whenever needed, without waiting for a specialist team to arrive. Parallel surveying at multiple sites becomes possible, boosting the project’s overall productivity. The reduction in setup and teardown of large equipment also shortens the time between tasks, making quick measurements during site operations convenient.

• Quality control and reduction of rework: By obtaining high-precision survey data on site at all times, construction errors and defects can be detected and corrected early. Regular smartphone surveying during construction helps prevent rework due to dimensional mismatches after completion. Since the site representative can measure and verify on the spot, variability in as-built results is reduced, contributing to consistent and improved construction quality. Real-time sharing of accurate as-built data smooths communication among stakeholders, helping prevent problems before they occur.

• Improved safety: Smartphone surveying also offers safety advantages for measurements in hazardous locations. Measurements at heights, steep slopes, or busy roads can be completed quickly, minimizing exposure time. Combined with drones or long poles, data can be collected safely from a distance. The elimination of carrying heavy surveying equipment reduces physical strain on workers. These factors help alleviate unsafe work conditions amid labor shortages, offering significant safety management benefits.

Thus, adopting smartphone + LRTK yields wide-ranging benefits such as easing labor shortages, improving efficiency, ensuring quality, and enhancing safety. In addition, because site personnel can perform certain surveying tasks without a dedicated surveyor, it helps resolve human-resource bottlenecks. Scenarios such as municipality staff immediately measuring and sharing damage at disaster sites have become realistic. The spread of smartphone surveying is a new trend that strongly accelerates DX (digital transformation) on construction sites.

Summary: the new normal of high-precision surveying

The world of high-precision surveying is undergoing a major change. Until now, the norm was that “precise measurement requires expensive equipment and specialized skills.” However, that norm is being rewritten by the combination of smartphones and LRTK. Pro smartphones are not necessary — the era has begun in which anyone can perform precise surveying with the smartphone in their hand without purchasing the latest high-end smartphone or surveying instruments costing hundreds of thousands of dollars.

By using simplified surveying with LRTK, even those without specialized surveying skills can quickly quantify site conditions and utilize data at speeds and accuracy that were previously unthinkable. This is not merely a replacement of equipment but a transformation of on-site workflows and a new normal. It aligns with the productivity improvements and labor savings sought in the i-Construction era, and smartphone + LRTK surveying will continue to expand.

With high-precision positioning technology now within reach, surveying is no longer the work of only a few specialists. With your smartphone and LRTK, you can perform centimeter-level measurements whenever needed. “Pro smartphones are not necessary!” — this is the new normal of high-precision surveying that LRTK brings. Consider adopting cutting-edge smartphone surveying technology to take the first step toward on-site efficiency and DX.

FAQ

Q: Can iPhone Pro LiDAR alone achieve high-precision surveying? A: For simple short-range measurements, iPhone Pro LiDAR can be somewhat effective. For example, room dimension measurements or 3D scans of small parcels of land can sometimes yield results with errors ranging from several centimeters to several tens of centimeters. However, for professional surveying that requires accuracy within a few centimeters or direct linkage to public coordinates, an iPhone alone has limitations. This is due to smartphone GPS errors and the issue that LiDAR point clouds remain in local device coordinates. To obtain accurate absolute coordinates or limit errors to a few centimeters, RTK-GNSS correction is indispensable. Therefore, iPhone Pro LiDAR is useful as an auxiliary tool for capturing shapes, but combining it with RTK-based position correction is what ensures surveying-level accuracy and reliability.

Q: What does LRTK do as a device? A: LRTK is a high-precision GNSS receiver for smartphones. It is a small device that attaches to a smartphone, receives satellite signals, and applies RTK corrections. With LRTK, a smartphone can perform real-time centimeter-level positioning. It acts as an attachment that turns a smartphone into a professional GPS surveying instrument, with an internal battery and antenna for all-in-one operation. In Japan, LRTK supports Michibiki’s CLAS augmentation signals, enabling high precision via satellite even in environments where base station communication is difficult, such as mountainous areas. Unlike traditional fixed RTK equipment, LRTK is pocket-sized and portable, designed as a high-precision positioning device that is easy to use on site.

Q: Can LRTK be used with ordinary smartphones rather than high-end Pro models? A: Yes — it can be used with commonly held smartphones. LRTK supports devices such as iPhone and iPad and connects via Bluetooth or a dedicated case, so no special modifications or expensive models are necessary; a standard smartphone becomes a surveying instrument. Of course, models with LiDAR like the iPhone Pro can fully utilize point cloud scanning features, but even smartphones without LiDAR can perform high-precision single-point positioning and photogrammetry, among many other capabilities. In short, because LRTK handles the high-precision positioning portion, the smartphone itself can be your usual model. You don’t need to worry that you must buy the latest Pro smartphone — you can start high-precision surveying with your existing smartphone plus LRTK.

Q: Is operation difficult? Can beginners use it? A: The operation is intuitive and designed to be easy for beginners. Attach LRTK to your smartphone and launch the dedicated app; then follow on-screen prompts and press buttons to record survey points or perform point cloud scans. You won’t need to perform complicated settings or manual calculations like with conventional surveying instruments. For example, tap the “measure” button at the point you want to measure and the coordinates will be corrected and recorded automatically. For staking out, the app displays the direction to the target point, and you simply move accordingly. Basic operations can be learned with short training, and people without surveying expertise can use it on site. Data sharing to the cloud and drawing generation are semi-automated in the app, so post-measurement workflows are also very smooth.

Q: What level of positioning accuracy is achievable? Is it really centimeter-level? A: Under appropriate conditions, nearly centimeter-level accuracy can be achieved. With LRTK performing RTK positioning, horizontal accuracy of about 1–2 cm (0.4–0.8 in) and vertical errors on the order of a few centimeters have been confirmed. This level of accuracy meets the standards typically required for civil engineering surveying and as-built control. However, accuracy depends on satellite reception conditions and the surrounding environment: open areas with multiple visible satellites yield the highest precision, whereas accuracy may decrease slightly in urban canyons or forests where the sky view is obstructed. Even then, the accuracy is far superior to conventional smartphone GPS. In any case, using LRTK enables positioning that rivals conventional specialized equipment, making it suitable for reliable surveying work. Measurement results can be checked in real time in the app, and indicators of accuracy (such as whether a Fix solution has been achieved) are displayed so you can monitor precision during operations.