LRTK at Construction Sites: Accurately Recording Orientation and Location Information in Photos

Table of Contents

• Challenges with site photos: insufficient location and orientation recording

• Benefits of photos with location information

• Advantages of also recording orientation information

• What is LRTK: achieving centimeter-level positioning with a smartphone

• Automatically tagging photos with location and orientation using LRTK

• Expected effects and use cases at construction sites

• Simple surveying with LRTK

• FAQ

At construction sites, many photos are taken to record and report construction progress. However, traditional methods have a problem: photos often do not sufficiently record where they were taken (location) or which direction they were facing (orientation). For example, when reviewing photos later, it can be unclear “which part of the site this photo shows” or “which direction the camera was pointing,” making the photos unusable as reliable documentation. This is especially true on large sites where many views look similar; if the shooting location or direction is ambiguous, it can cause confusion about which photo corresponds to which place.

Also, linking location and direction information to photos typically requires supervisors to take handwritten notes at the time of shooting or to include site names and directions in photo filenames, which is a significant burden. Standard smartphone cameras can add GPS-based location data, but that accuracy can have errors on the order of several meters (several ft), which is insufficient for construction purposes. Furthermore, organizing the photos afterward and compiling ledgers or reports is cumbersome. These conventional photo-recording methods have left much potential of site photos untapped.

The main problems with traditional site photo management are summarized as follows:

• Inability to identify the shooting location: Photos do not retain precise coordinates, so later it can be unclear “where this photo was taken.”

• Unknown shooting orientation: The direction the camera faced is not recorded, making it hard to understand the subject or coverage in the photo.

• Time-consuming photo organization: After shooting, photos must be plotted on maps or have place/direction added to filenames, requiring manual work.

Benefits of Photos with Location Information

If photos include accurate location information (coordinates), their value increases dramatically. First and foremost, it becomes immediately clear “where a photo was taken,” preventing recording mistakes and misunderstandings. With latitude, longitude, and elevation data, it is easy to plot each photo’s shooting point on a map for visual management. For example, pinning photo locations on a construction area map makes it intuitive to see which area each image represents.

Photos with location data are also useful for progress management and reporting. By periodically photographing the same points, you can track changes over time. If you collect photos at specific shooting points from before construction to completion, it becomes easier to review progress later. Moreover, accurate coordinates in photo data serve as evidence for quality control and safety management. Because it is clear when and where a photo was taken, you can accurately trace back site conditions if a problem arises later, aiding in root-cause analysis and planning countermeasures.

If photo location data are recorded in a common coordinate system, they can be easily integrated with other survey data. For example, you can cross-check a point on drawings with photos or measure distance relationships among photos for spatial analysis. Photos with location information thus become useful geospatial data for managing site information, not merely records.

Advantages of Also Recording Orientation Information

In addition to location, recording the camera’s orientation at the time of shooting further enhances the usefulness of site photos. Orientation information indicates which direction the camera was facing relative to north when the photo was taken (for example, northeast). This information clarifies the directional relationships of objects shown in the photo.

One advantage of photos with orientation is that you can accurately determine which direction of the site the photo documents. For example, if you take photos facing north, east, south, and west from the same point, you can immediately judge which aspect of the site each photo represents. Information that previously required handwritten notes like “photo taken facing XX direction” would be automatically embedded in the photo data, helping to prevent oversights and mix-ups.

Photos that include orientation are also useful for analyzing the overall site layout. If you display the shooting point and direction as arrows on a map, you can visually see which area was photographed from which angle. This is convenient for sharing information among stakeholders and allows people in remote offices to form a three-dimensional impression of the site from photos. For example, when reporting site conditions to clients or subcontractors, orientation-labeled photos let you easily explain “this is the structure as seen from the south,” facilitating smoother communication.

In short, photos that contain both location and orientation significantly improve the accuracy and reliability of site records. Accumulating such data creates an asset useful for future construction planning and inspections.

What is LRTK: achieving centimeter-level positioning with a smartphone

LRTK was developed to solve these problems. LRTK is a system consisting of an ultra-compact RTK-GNSS receiver device that can be attached to a smartphone and a dedicated app, transforming a handheld smartphone into surveying equipment capable of centimeter-level (half-inch-level) positioning. Developed by a university-born startup, it brings the latest GNSS positioning technology to the field in an easy-to-use form.

RTK stands for Real Time Kinematic, a technique that applies real-time corrections to GNSS positioning errors to achieve high accuracy. While standard GPS positioning can have errors of about 5–10 m (16.4–32.8 ft), RTK uses correction data from a base station to achieve errors of a few centimeters or less. LRTK incorporates an RTK-capable high-performance antenna and pairs with a smartphone to provide stable centimeter-level positioning in the field.

The LRTK device itself is compact enough to fit in a pocket and can be easily attached to smartphones (currently mainly iPhone and iPad). Compared with traditional heavy surveying equipment that required several people to carry, the smartphone-plus-small-device configuration is revolutionary because it allows anyone to carry and operate it with ease. For example, even without survey specialists on site, field technicians can quickly take measurements and record data, so each person effectively carries a “surveying instrument in their pocket.” With LRTK, you can perform many measurement and recording tasks with a single device: measuring positions, taking photos, performing point-cloud scans, staking out positions, and checking with AR overlays. In short, smartphones are becoming full-fledged high-precision surveying tools.

LRTK also supports CLAS, the high-precision augmentation signal provided by Japan’s Quasi-Zenith Satellite System (Michibiki). This allows high-precision positioning even at sites without cellular connectivity—such as mountainous areas—by receiving correction data directly from satellites without internet access. Of course, network-based RTK corrections (Ntrip services) can also be used, so centimeter-level positioning can be obtained stably anywhere in Japan.

Automatically tagging photos with location and orientation using LRTK

LRTK does more than just measure high-precision positions. It also dramatically simplifies the recording of location and orientation information in photos, the topic of this article. The dedicated app includes a “positioning photo” feature that automatically tags photos taken with the smartphone camera with precise coordinates (latitude, longitude, elevation) of the shooting point and the camera’s facing direction. By simply pressing the shutter in the field, positioning data are recorded along with the photo, eliminating the need to manually write down locations or note directions after shooting.

Using this feature significantly reduces missed shots and recording errors. For example, with standard smartphone GPS the error can be large and you might think you’ve tagged a photo correctly when the actual location is off, but with LRTK you can always attach accurate location tags at centimeter-level (half-inch-level) precision. This prevents situations where “you don’t know where a photo was taken,” and even beginners can record reliably. The app also displays the current positioning quality (RTK reception status) in real time during shooting, allowing you to take photos when accuracy is assured. Less experienced users can follow on-screen prompts to confirm RTK is Fix (in a stable state) before taking the shot, ensuring high-precision data. If RTK positioning is not available on-site, recording can continue with normal GPS accuracy, allowing flexible operation while using RTK whenever possible for critical records.

Photo data taken with LRTK that include location and orientation can be automatically uploaded to the cloud and organized on maps. Because each photo is linked to coordinates, uploading to a cloud service will plot shooting points on a map and manage photo lists in chronological order. This removes the need to name photo files or paste them into Excel ledgers manually, eliminating human error in organization. Photos taken in the field can be organized into a cloud-based map album the same day, making office report preparation smoother.

Expected effects and use cases at construction sites

By using photos with high-precision location and orientation information, various benefits can be expected at construction sites. Key points include:

• Improved recording accuracy: Eliminating errors in position and direction greatly enhances the reliability of photo records. This reduces rework such as returning to the site after discovering a “recording mistake,” contributing to consistent construction quality.

• More efficient progress management: Because photos are organized on a map and viewable in time series, you can intuitively track construction progress. Lining up fixed-point photos makes it easy for all stakeholders to share pre- and post-construction changes and reduces the effort needed to prepare reports.

• Enhanced information sharing: Coordinate-tagged photos can be easily shared via the cloud, allowing remote stakeholders to virtually experience site conditions. When site managers and clients view the same photos and maps, fewer misunderstandings occur and decisions can be made more quickly.

• Stronger safety and quality management: With precise location and timestamps recorded for each photo, they serve as reliable evidence for as-built and safety management. If issues arise, you can accurately confirm “when, where, and what the conditions were” from the photos, aiding investigation and corrective measures.

• Integration with survey data: Having consistent location data makes it possible to overlay photos with point-cloud data from drones and other sources. You can measure dimensions not visible in photos from point clouds, enabling combined data use that advances site visualization and digital transformation.

Thus, introducing LRTK and using high-precision positioning photos can greatly evolve how construction sites record and manage information. Simple photo shooting becomes a “digital archive of the site” with accurate spatial information, contributing to overall efficiency and quality improvements.

Simple surveying with LRTK

LRTK’s utility goes beyond photo records. The ability to easily handle centimeter-level (half-inch-level) positioning makes it a very useful tool for simple on-site surveying. Without specialized equipment or deep expertise, field staff can quickly take necessary measurements with LRTK, helping to address shortages of surveyors and reduce costs.

For example, the LRTK app can save current position coordinates for use in drawings with the press of a button, calculate distances between two points or the area of an enclosed space on the spot, simplifying surveying tasks. Combined with iPhone or iPad cameras and LiDAR, multiple photos can be used to generate high-precision 3D point-cloud models to calculate earthwork volumes (cut and fill), or overlay planned alignment lines on-site in AR to compare drawings with actual terrain—tasks previously performed only by specialists can now be done quickly by anyone. In other words, LRTK expands the range of surveying work that non-experts can perform.

This easy-to-use, high-accuracy system truly embodies the concept of “simple surveying.” With only a smartphone, LRTK is immediately usable and is a strong ally for small to medium sites and municipal infrastructure inspections. As the era in which each person carries a mobile surveying device becomes reality, flexible on-site operations that stray from conventional practices are possible. As a first step toward on-site digital transformation (DX), consider utilizing LRTK.

FAQ

Q: What is LRTK? A: LRTK is a set of a small GNSS receiver device that connects to a smartphone and a dedicated app that together convert a smartphone into surveying equipment capable of centimeter-level (half-inch-level) positioning. Using the Real Time Kinematic (RTK) method, it acquires high-precision location information in real time for use in photo shooting, point-cloud measurement, and various field tasks.

Q: How is it different from photos taken with a normal smartphone? A: Normal smartphone photos can include location data, but the accuracy is coarse—about 5–10 m (16.4–32.8 ft)—and orientation (the direction the camera faced) is not recorded. With LRTK, you can obtain precise coordinates to the centimeter level and the camera’s orientation is automatically recorded for each photo, making it clear where and in which direction a photo was taken.

Q: Can it really achieve centimeter-level accuracy? A: Yes—if RTK correction information is properly received, horizontal accuracy of about 2–3 cm (0.8–1.2 in) and vertical accuracy of about 3–4 cm (1.2–1.6 in) can be expected. Accuracy varies with satellite reception conditions, but the LRTK app allows you to monitor accuracy in real time while working, so you can perform photo shoots and measurements when high accuracy is assured. If RTK is unavailable, standard GPS accuracy (several meters (several ft)) will apply, but by confirming RTK is Fix during critical recordings you can maintain high precision.

Q: Can it be used indoors or at sites without communication coverage? A: If you can receive satellite signals outdoors, LRTK can be used even without communication coverage. LRTK can receive the CLAS augmentation signals from Japan’s Michibiki satellites, enabling centimeter-level positioning at sites without internet access, such as mountainous areas. However, in fully indoor or underground locations where satellite signals do not reach, RTK positioning is difficult. In such cases, you can obtain a reference coordinate outdoors first and then estimate indoor positions using the smartphone’s AR features in a relative positioning mode.

Q: Are specialized skills or qualifications required to operate it? A: No special qualifications are required. The LRTK app is designed for intuitive operation, and anyone familiar with basic smartphone use can operate it. Positioning and photo capture are simple, mostly single-button operations; complex settings and calculations are handled automatically by the app. With brief instruction, even staff who are not tech-savvy or new employees can quickly start using it for field records.

Q: What is needed to introduce LRTK? A: To use LRTK, you need the LRTK device (an RTK-capable GNSS receiver), a compatible smartphone (currently iPhone/iPad, etc.), and the dedicated LRTK app. After initial setup, attach the device to the smartphone and launch the app to start positioning. High-precision RTK requires correction information, which can be obtained via internet-based Ntrip services, or in Japan you can receive Michibiki (CLAS) signals to perform corrections without communication. In other words, you can start high-precision positioning without installing a special base station.

Q: Is the effect worth the introduction cost? A: The efficiency gains from LRTK are expected to outweigh the costs. For example, labor and days required for photo recording and surveying can be greatly reduced, and the effort to prepare reports and conduct site checks is decreased. Tasks previously outsourced to surveying contractors can be handled in-house, reducing costs. Accumulated data can improve future construction planning accuracy and support knowledge transfer. Considering productivity improvements and risk reduction from site DX, the return on investment from LRTK should be substantial.