High-Precision Photogrammetry Cuts Man-Hours by 50%: The Power of LRTK Smartphone Positioning

Introduction

The construction and civil engineering industries are seeking efficiency gains in on-site surveying by leveraging digital technologies. Chronic labor shortages and an aging population of surveying technicians also make labor-saving measures to operate sites with limited personnel a major issue. Among the approaches, photogrammetry (photogrammetry) has attracted attention as a method to create 3D models and drawings by photographing the site with a camera. However, conventional photogrammetry and surveying work have required significant effort and time, as well as specialized knowledge and manpower. This article explains why and how an innovative solution called LRTK, which combines smartphones and RTK technology, can reduce photogrammetry man-hours by 50%. We introduce the latest trends that turn smartphones such as the iPhone into tools for high-precision positioning, making precision photogrammetry easily accessible to anyone.

Current State and Challenges of Photogrammetry

Photogrammetry is a technology that generates three-dimensional information (point cloud data and orthophotos) of terrain and structures from multiple images taken by drones or ground cameras. Driven by the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* initiative, aerial photogrammetry (drone surveying) that can efficiently measure wide areas is becoming widely used on sites. Drone photogrammetry excels at recording large-area terrain from the air in a short time, allowing data acquisition that is lower-cost, faster, and safer compared with traditional manual surveying. On the other hand, turning photogrammetry data into accurate surveying results has involved time-consuming image processing and additional tasks such as installing ground control points to improve accuracy. Drone operation also requires pilot qualifications, permits, and expensive equipment, which can be a high hurdle for small sites or emergency situations. Furthermore, in indoor spaces where drones cannot fly or on the underside of bridges, close-range photogrammetry from the ground is required, but it can be difficult to obtain sufficient measurements when people cannot approach hazardous areas.

Conventional ground surveying has used tape measures, leveling rods, and total stations with teams of two to three people measuring each survey point sequentially from reference points. This method incurs significant labor costs, and it is not uncommon for surveying alone to take a full day or more on large sites. Manual measurements also carry the risk of human error; misreads or recording mistakes that require re-measurement can delay schedules. In terms of efficiency, survey points were sometimes reduced, leading to missed defects in unmeasured areas.

Thus, current photogrammetry and surveying face challenges in both “time and effort” and “ensuring accuracy.” In particular, as labor shortages and aging technicians progress, methods that can achieve high accuracy with a small number of people are in strong demand. This has led to approaches that utilize high-precision GNSS (Global Navigation Satellite System) technology on site. Among them, the RTK (Real Time Kinematic) method, which improves positioning accuracy in real time, has attracted attention as a key to solving conventional problems.

High-Precision Positioning with RTK and Smartphone Use

RTK is a technology that enhances positioning accuracy to centimeter-level by correcting position errors in real time between two GNSS receivers (a base station and a rover). Standalone GPS positioning typically has errors of about 5–10 m, but with RTK, high-precision position information within a few centimeters horizontally and vertically can be obtained. Since the 1990s, RTK-GNSS surveying equipment has become widespread as an alternative to optical methods. However, conventional RTK equipment has often been stationary, expensive, and required specialized knowledge—making “high accuracy but lack of ease of use” a bottleneck.

Recently, smartphone-compatible compact RTK receivers have made RTK positioning more accessible. For example, by using an RTK-GNSS device that can be attached to a smartphone and weighs only 165g with a thickness of about 1 cm (0.4 in), a palm-sized smartphone instantly becomes a high-precision positioning instrument. A smartphone’s GPS accuracy is usually several meters, but when combined with an external RTK device, positioning error can be reduced to a few centimeters. This allows surveying work that previously required multiple people and large equipment to be completed with a single smartphone (plus a small device), enabling precise position measurement and photogrammetry by one person. The advent of smartphone RTK positioning is expected to achieve both labor savings and sophistication in surveying.

How LRTK Works and Its Features

LRTK (LRTK) is a solution consisting of an ultra-compact RTK-GNSS receiver that can be used integrated with a smartphone and a dedicated app. Simply attaching the LRTK device to an iPhone or iPad enables real-time acquisition of centimeter-level position information (half-inch accuracy). Its features are summarized as follows:

• High-precision positioning: The built-in high-performance antenna receives multi-frequency satellite signals and, with RTK corrections, can achieve positioning accuracy of approximately ±2 cm (±0.8 in) horizontally. Vertical accuracy is similarly within a few centimeters, allowing acquisition of latitude, longitude, and height (elevation). It also supports Japan’s plane rectangular coordinate system, so measurements can be used directly in design drawings and GIS.

• Lightweight and compact: The device itself is light at about 165g and has a thickness of about 1 cm (0.4 in). It can be attached to the device in one touch with a dedicated case or magnetic attachment, integrating with the smartphone and fitting into a pocket. There is no need to carry heavy tripods or equipment, and it offers mobility to be taken out and used immediately when needed.

• Built-in battery and long operation time: The LRTK device has a built-in battery that runs continuously for about 6 hours. It can be charged and powered via USB Type-C, so with a mobile battery you can use it all day on site without worrying about power running out.

• CLAS and network support: It can receive high-precision augmentation signals (CLAS) provided by Japan’s quasi-zenith satellite system “Michibiki,” enabling standalone RTK positioning even in mountainous areas out of cellular coverage. It also supports the Ntrip method via the Internet, providing stable correction information anywhere in Japan.

• Intuitive dedicated app: The iOS “LRTK app” allows unified operation from positioning to data management. In addition to basic functions such as one-tap measurement and recording of the current position, continuous positioning for movement track logs, and averaging multiple measurements to improve accuracy, it includes abundant features such as point cloud scanning, coordinate navigation, AR display, and photogrammetry mode described later. The interface supports Japanese and is easy for beginners to understand, allowing operation by following prompts without specialized knowledge.

• Full-fledged surveying by one person: LRTK can also be used mounted on a monopod or a pole with a ferrule at the tip, enabling stable point measurements and stakeout operations like full-fledged surveying equipment. The app makes it easy to set height offsets, and by leveling with a bubble vial, accurate positioning is possible even with one hand. Tasks that formerly required two people for stake placement can be done by one person with LRTK.

As described above, LRTK is an all-in-one surveying system that integrates the smartphone’s camera and sensors with a GNSS device and the cloud. Pocket-sized hardware handles high-precision positioning, the smartphone provides a user-friendly UI and imaging functions, and cloud services support data storage, sharing, and analysis—together delivering versatility comparable to a full set of conventional surveying equipment.

Benefits of High-Precision Photogrammetry Enabled by LRTK

So what advantages does photogrammetry gain by utilizing LRTK? Here are the main points:

• Significant reduction in man-hours: High-precision photogrammetry shot with a smartphone and LRTK dramatically shortens the effort and time for on-site measurement. An area that previously took an all-day surveying team to capture in 3D can now be completed by one person simply walking the site with a smartphone and taking photos. Since dimensions can be obtained from the resulting 3D model, there is no missing measurement points and the need for additional re-surveying is reduced. In actual sites, there are examples of approximately 50% reduction in man-hours compared to drone photogrammetry or manual surveying.

• Feasible with few people or solo work: LRTK enables high-accuracy surveying even when experienced surveyors are scarce, allowing small teams to perform precise surveys. Anyone who can operate a smartphone can use it, enabling single-person surveys and distributed work. For example, team members can simultaneously measure different locations with their own smartphones, eliminating waiting times for surveying and improving overall construction efficiency.

• Low cost and easy to introduce: With a simple setup of a smartphone and a compact RTK device, you can start centimeter-accurate photogrammetry without investing in expensive surveying equipment. Using existing smartphones in-house reduces initial investment, making it easy for small and medium-sized companies or local governments to adopt. Because the operation is intuitive without specialized training, new staff can become effective on site quickly.

• High accuracy and reliable results: Photos taken with LRTK smartphone positioning have accurately recorded absolute coordinates (world coordinates) and camera orientation. GPS coordinate tags on each photo improve scale and alignment accuracy during point cloud reconstruction by photogrammetry software, producing 3D models that match site coordinates precisely. If necessary, using ground control points in combination can keep absolute accuracy within a few centimeters, yielding survey results with reliability comparable to conventional methods.

• Improved safety and speed: Smartphone photogrammetry allows measurements from a distance without personnel entering hazardous areas. For example, even a large intersection with a side length exceeding 50 m (164.0 ft) was precisely scanned solely by photographing from the surroundings without workers entering the roadway. In disaster sites, rapid modeling of damaged areas aids damage assessment and recovery planning. Shortening surveying work also speeds up overall construction and reduces worker burden.

• Data utilization and cloud integration: Point clouds and photos captured with LRTK are automatically uploaded to the cloud, enabling office staff to check the site’s 3D model and share it with stakeholders in real time. This greatly shortens the days spent on post-survey data organization and drafting, streamlining reporting and inspection processes. Since each photo is tagged with date and position, it is easy to perform time-series comparisons and record construction processes. Volume calculations and cross-section creation can be done immediately on site, allowing versatile use of survey data.

LRTK’s Multifunctionality Useful on Site (Point Cloud, AR, Cloud)

LRTK also includes various functions that contribute to on-site productivity beyond photogrammetry. For example, the 3D point cloud scan function uses the iPhone’s LiDAR sensor and camera to scan surrounding terrain and structures, generating high-precision point cloud data on the spot. Thanks to RTK-based current position correction, the position drift and distortion accumulation that were problems with smartphone-only scanning are less likely to occur, and accurate point cloud models can be obtained even when walking over wide areas. Generated point clouds can be previewed immediately on the smartphone and, if needed, saved to the cloud for detailed analysis or drawing creation.

The AR (augmented reality) display function is another powerful tool of LRTK. By loading design drawings or 3D model data into the app in advance, these can be overlaid on the real scene through the smartphone camera. High-precision alignment allows design lines and BIM models to be projected onto the actual ground or structures without offset, enabling instant verification of whether construction locations and heights match the design. Visualization of buried pipes or boundary data via AR helps warn workers during excavation and aids as-built inspection.

Additionally, LRTK’s coordinate navigation feature guides stakeout and reference points. The smartphone screen shows the direction and distance to the target point in real time, and by following the arrow, you can reach the designated position with centimeter accuracy. Even inexperienced workers can place stakes accurately without hesitation, contributing to labor savings and improved accuracy.

Finally, cloud integration should not be overlooked. Data captured and measured with the LRTK app is automatically saved to the cloud and can be shared among stakeholders. Office PCs can immediately review on-site point clouds and photos to give instructions, and reports can be prepared the same day based on on-site information—enabling real-time information sharing. The cloud also allows distance and area measurements, and point cloud downloads for detailed analysis, making smooth collaboration between site and office a reality.

Conclusion: Start Simple Smartphone Surveying with LRTK

Methods for 3D surveying, including photogrammetry, have become dramatically more accessible through the combination of smartphones and compact devices. By utilizing LRTK, precise site surveying is possible with just an iPhone, significantly reducing the man-hours required for surveying tasks. The era is arriving in which cumbersome equipment and large crews are no longer necessary, and each on-site technician can perform “simple surveying” with their own smartphone.

In practice, there have been reports that even newcomers achieved high-precision surveying results thanks to intuitive smartphone app operation, with comments from the field such as “work has become easier because accurate coordinates are recorded just by taking photos” and “waiting time for surveying has decreased and construction proceeds more smoothly.” Local governments have also started introducing smartphone surveying; for example, Fukui City streamlined disaster-site surveying using iPhone high-precision positioning, contributing to faster recovery and cost savings.

High-precision photogrammetry dramatically improves the quality and speed of construction management and addresses challenges such as labor shortages and safety. In construction and civil engineering sites, smartphone surveying with LRTK can be the trump card for productivity improvement. With the latest digital technologies on your side, why not realize smart site operations that cut man-hours by 50%? With a smartphone and LRTK, surveying can be easier and more reliable than ever.