Photogrammetry + AR New Technology: Solo High-Precision Surveying Enabled by Smartphone RTK

In recent years, digital technologies such as photogrammetry and AR (augmented reality) have been rapidly adopted at construction and civil engineering sites. By 3D-measuring sites with drones or smartphones and visualizing that data in AR, surveying tasks that previously required several people can now be performed efficiently by a single person. The advent of smartphone RTK—high-precision GNSS receivers that attach to smartphones—has also been revolutionary, making it easy to obtain centimeter-level position information (cm level accuracy, half-inch accuracy). This article explains the new technology created by the fusion of photogrammetry and AR and introduces the benefits and concrete use cases of solo high-precision surveying enabled by smartphone RTK. We deliver the latest trends combining technical depth and practical utility for construction and civil engineering site managers, surveying company engineers, and municipal infrastructure administrators.

What is photogrammetry?

Photogrammetry is a technique that reconstructs the three-dimensional shape of objects from multiple photographs of a site to assist in surveying and measurement. Using high-resolution cameras or drones to photograph terrain and structures from various angles, software matches feature points across images to generate point cloud data and 3D models. Point cloud data obtained by photogrammetry represent the surface of the ground and structures as a collection of countless coordinate points. This is essentially a digital copy of the real space and records detailed information that conventional plans or 2D photos cannot fully capture.

Photogrammetry has recently become widely used in the construction industry. For example, aerial photogrammetry using drones makes it possible to create 3D models of large areas of existing terrain in a short time. Where land surveying once required surveyors to spend days measuring points one by one with a total station, drone photogrammetry can achieve a dramatic reduction in time. In fact, there are reports of surveys that took two days by manual work being completed in 0.5 day with drone photogrammetry, and 3D surveying using point cloud data dramatically improves productivity. Point clouds acquired by photogrammetry can also be used for comparison with design data and analysis, automating tasks such as creating terrain cross-sections and volume calculations, which is useful for planning construction and for as-built inspections.

Use of AR technology at construction sites

AR (augmented reality) overlays digital information onto the real landscape, and its use is beginning at construction and civil engineering sites. By overlaying structural models from design drawings or surveying data onto the actual field view through a tablet or smartphone screen, AR can visualize information that is difficult to intuitively understand from drawings or numbers alone. For example, you can share a construction image by displaying a 3D model of the planned completed structure on site in AR, or confirm the location of underground pipes by viewing them transparently from the road surface.

Using AR technology on site improves the efficiency and accuracy of construction management and surveying work. For clients and site staff alike, seeing life-size digital models on site facilitates shared understanding and smooths communication. However, accurate overlay in AR requires high precision in the device’s position and orientation. Standalone positioning (GPS) and attitude estimation of a smartphone or tablet have large errors, and when AR is displayed over a wide area it has been problematic that data misalignment or scale distortion occurs. This is where high-precision positioning technology using smartphone RTK becomes important.

Centimeter-level positioning with smartphone RTK

RTK stands for Real Time Kinematic, a technique that applies correction information to satellite positioning such as GPS to dramatically improve positioning accuracy. Standalone positioning typically has errors of about 5–10 m (16.4–32.8 ft) due to satellite signal errors, but RTK can reduce those errors to a few centimeters (a few inches). Specifically, correction data from a base station installed at a known location—delivered in real time via services such as internet-based NTRIP or Japan’s quasi-zenith satellite “Michibiki” centimeter-level positioning augmentation service (CLAS) (cm level accuracy, half-inch accuracy)—are applied to the rover’s GNSS measurements to realize high-precision relative positioning.

Recently, RTK surveying has become easy to use with smartphones. Smartphone RTK refers to the technology of attaching a compact RTK-capable GNSS receiver to a smartphone or tablet, enabling the mobile device itself to achieve centimeter-level positioning (cm level accuracy, half-inch accuracy). For example, by connecting an attachable dedicated GNSS receiver to a smartphone and accessing a correction information service, the smartphone can receive high-precision real-time position data. It is groundbreaking that centimeter-level positioning, which previously required expensive surveying equipment or fixed GPS base stations, can now be achieved with a single pocket-sized device. In practice, RTK units have emerged that deliver typical accuracies of around 2–3 cm (0.8–1.2 in) and, when stationary, average errors of less than 1 cm (<0.4 in) simply by attaching a receiver weighing approximately 125 g to a smartphone.

Smartphone RTK dramatically increases the reliability of positional information. High-precision coordinates can be attached to 3D point clouds obtained by photogrammetry or iPhone LiDAR scans, enabling the creation of absolute-coordinate 3D models without worrying about position misalignment or distortion. This makes it possible to accurately compare point cloud data acquired on site with design drawings or other survey results and to stitch multiple scan datasets together with high conformity. When high-precision alignment is ensured, AR overlays of digital information will match the real world precisely, achieving a seamless fusion of reality and digital data.

Solo high-precision surveying enabled by new technology

The combination of photogrammetry + AR + smartphone RTK brings the prospect of performing high-precision surveying alone, a task that used to require specialist teams and expensive equipment. For example, where 2–3 surveyors were once needed for terrain surveys, a single person can create a 3D map of a large site in a short time by shooting with a drone and an RTK-equipped camera. Also, staking out with a total station can be completed solo by displaying coordinates from the drawings on site in AR via smartphone RTK. The labor of carrying heavy tripods and prisms back and forth or coordinating with assistants is eliminated, greatly improving work efficiency.

The ability to perform surveys solo has significant implications for addressing labor shortages and workstyle reforms in the construction and civil engineering industries. Even without many experienced surveyors, if site supervisors or foremen—who are not surveying specialists—can “take a quick measurement themselves,” construction delays and schedule losses due to waiting for survey crews can be reduced. Lowering the barrier to surveying through new technology makes it possible for limited personnel to cover multiple sites, improving productivity. Additionally, digitized data can be shared via the cloud immediately, allowing survey results acquired on site to be shared with the office on the same day and enabling rapid revisions to construction plans and decision-making—contributing to faster management.

From a safety perspective, solo high-precision surveying also offers advantages. For example, in dangerous slope areas or deep excavations, data can be acquired via photogrammetry or scanning remotely, enabling shape measurement without personnel entering hazardous zones. AR-assisted work can also help prevent misunderstandings and human errors on site. Thus, solo surveying using new technologies brings major benefits not only in labor saving but also in safety assurance and quality improvement.

Major use cases in construction and civil engineering

Solutions that combine photogrammetry, AR, and high-precision positioning are being used in various situations in construction and civil engineering. Below are several concrete use cases expected on site.

• Current terrain 3D surveying: Using point cloud data for pre-design terrain surveys allows rapid acquisition of detailed digital terrain models (DTMs) and contour lines. Automatically generating terrain maps from point clouds obtained by drone photogrammetry or terrestrial LiDAR scanning is far more efficient than traditional methods. Large-area surveys can be handled by a single person, significantly shortening survey periods.

• As-built inspection and quality checks: Structures after concrete placement or earthworks can be fully recorded as point clouds and compared with design models on site to verify whether the finish matches the drawings. For example, overlaying post-construction point clouds with BIM models and displaying deviations as a heat map makes it immediately clear which areas are overfilled or undercut relative to the design. AR-capable apps can display heat maps overlaid on the actual object on site, allowing intuitive identification of areas needing repair and evolving quality control into a real-time improvement tool.

• Visualization of construction progress: Regularly scanning the site by phase enables quantitative grasping of work progress from point cloud data. Comparing weekly or monthly point clouds with planned models from the schedule and displaying the unconstructed 3D model together with the constructed point cloud in AR provides intuitive on-site understanding of progress. Early detection of delayed areas or discrepancies in earthwork quantities compared with design helps improve schedule management and progress reporting accuracy.

• Earthwork calculation and progress management: Point clouds are powerful for volume calculations. Where the volume of piled soil was once estimated from sample points, accurate excavation and embankment volumes can now be calculated from differences between pre- and post-construction point clouds. Cloud-based tools allow one-click measurement of volume in a specified area from point cloud data. In the future, smartphone AR could display spatially “This embankment needs ○○ cubic meters more,” making quantity management intuitive and accurate through point cloud + AR.

• Survey guidance and staking-out: With high-precision AR displays, guiding survey points and staking out is easy. If coordinates of stake positions or structure corners from the design drawings are visualized in AR, a worker can see a “virtual stake” through the smartphone screen. Simply following arrows displayed on the smartphone will bring even inexperienced workers to the required position, enabling accurate staking-out. There is also potential for using smartphone AR to convey excavation depth and direction to heavy equipment operators, realizing smart construction that does not rely on surveying experience.

Applications in infrastructure management and disaster response

Photogrammetry combined with AR + RTK is also highly effective for infrastructure inspection and disaster response. For municipal infrastructure managers, maintaining existing structures and assessing post-disaster conditions are important tasks, and 3D data and AR are useful tools in these areas.

In routine infrastructure inspections, structures such as bridges and tunnels can be scanned with laser scanners or photogrammetry, and comparing current point clouds with past data allows objective evaluation of aging changes. Cracks, settlement, and deformation of members can be confirmed by 3D differencing, which is more accurate and efficient than flipping through paper drawings or photo albums for visual comparison. Photographs or notes of deteriorated areas can be linked to the acquired point cloud model and later projected on site in AR, enabling confirmation of repair plans made in the office while at the location. In the future, advanced systems that overlay past data and instruction information in the inspector’s field of view using AR glasses are also being considered.

In disaster response, the new surveying technologies are powerful. For large-scale landslides or earthquake damage, it used to take time for specialist contractors to measure or for aerial photo analysis, but now responders can instantly record damage in 3D on site with a smartphone in hand. For example, photographing a collapsed slope with a drone or smartphone and converting it to a point cloud enables on-site estimation of the volume of collapsed soil and rapid planning of restoration. There are cases where smartphone RTK devices compatible with quasi-zenith satellite augmentation signals were used in earthquake zones without cellular coverage, enabling precise recording of damage even in remote mountainous areas. Tools that can measure accurately anytime and anywhere without relying on networks offer major advantages in emergency mobility. Being able to acquire data without physically entering dangerous post-disaster sites also reduces the risk of secondary disasters.

High-precision surveying with a smartphone: Simple operation and benefits of LRTK

Finally, as an example of a simple solution to realize photogrammetry + AR + RTK, we introduce LRTK. LRTK is a system comprising a compact GNSS receiver that enables centimeter-level positioning for a smartphone and a dedicated app. By simply attaching it to a phone, the device transforms into a pocket-sized, versatile surveying instrument that allows a single person to easily perform high-precision surveys. The operation steps and main benefits are as follows.

• Preparation (setup): Attach the LRTK receiver to the smartphone or tablet to be used for measurement with one touch and launch the app. In Japan, connect to RTK correction services such as Michibiki CLAS or internet-based VRS; after waiting several tens of seconds, the system will reach a state where centimeter-level positioning is possible (RTK fixed solution). No complicated equipment setup or specialist knowledge is required, so it can be used on site immediately.

• Measurement (scan): You can start a 3D scan simply by walking around the target or area with a smartphone in hand. Press the button in the app to begin measuring, and slowly move the smartphone’s built-in camera or LiDAR sensor; high-precision coordinates will be attached to the acquired point cloud data in real time. Walking around for a few minutes is enough to complete point cloud measurement of the required area. The app displays the coverage area as you scan, enabling complete data collection without omissions. Because the operation is intuitive and requires no special skills, site staff can perform surveying themselves.

• Data utilization: After the scan is complete, a detailed 3D point cloud is displayed on the smartphone. Since the acquired data is already aligned with known coordinate systems (such as plane rectangular coordinates and elevation), it can be used immediately on site to measure distances, areas, and volumes. For example, you can measure the distance between any two points on the point cloud or view cross-sections to check thickness on site. With one tap in the app you can upload data to the cloud, making it easy to share and check point clouds on office PCs. Advanced analyses such as automatic removal of noise points (people or machines) from point clouds and difference color mapping by comparison with design drawings are supported on cloud services. Processes that previously required outsourcing to specialists or lengthy processing with dedicated software can now be completed with a single smartphone, enabling smooth end-to-end data utilization from site to office.

The greatest advantage of using LRTK is that “anyone, immediately, anywhere” can perform high-precision surveying. On site, stress from waiting for machines or survey inspections is reduced, and necessary measurements can be carried out whenever needed. For managers, in-house handling of point cloud measurement that was previously outsourced to surveying companies can reduce costs. For municipalities, staff collecting infrastructure inspection data themselves can reduce contracted work and improve emergency response capability. LRTK is already being adopted by construction companies and local governments and has proven useful in situation assessment at disaster sites and maintenance of urban infrastructure. The new technology combination of photogrammetry + AR + smartphone RTK can be considered the trump card of surveying DX that balances expertise and on-site practicality. Please consider introducing solo high-precision surveying with LRTK to dramatically improve site productivity and safety.