A New Era in Surveying: A Field Revolution with the Fusion of Photogrammetry and RTK — High-Precision, Instant Surveying with a Smartphone

A major technological innovation is now taking place on surveying sites in construction and civil engineering. The fusion of photogrammetry and RTK (real-time kinematic) technology has ushered in an era in which sites can be measured with high precision and instantly using only a smartphone. This article explains the latest trends in surveying using photogrammetry × RTK, introduces how simple, high-precision surveying with a smartphone works and its benefits, and explores related technologies that support next-generation surveying, such as point cloud scanning, AR (augmented reality), and cloud integration. At the end of the article we also introduce LRTK as a solution that makes it easy to adopt these new technologies. Experience the innovative methods that are opening a new era in surveying.

What is photogrammetry?

Photogrammetry is a technique for measuring terrain, structures, and dimensions from photographs. Using specialized software, common points are extracted from multiple photographic images to generate 3D models and point cloud data. It is rapidly spreading in construction and civil engineering because accurate measurements of target objects can be obtained not only from aerial photogrammetry using drones or high-mounted cameras, but also from ground-based photography. A major advantage of photogrammetry is that it can record large areas of a site in a short time and can safely survey hazardous areas that people cannot enter. In addition, because images obtained can be used to create orthophotos (distortion-free photographic maps as seen from above) and detailed topographic maps, it becomes easier to intuitively grasp the site conditions compared with traditional surveying methods.

However, photogrammetry alone can sometimes have limits in the accuracy of positional information obtained. Standard photogrammetry aligns the overall model based on geotags attached to photos and a few known control points (control points). But geotags acquired by smartphones or ordinary cameras often have large GPS errors, and meter-level offsets can frequently occur. Therefore, additional control surveys or alignment to known points were required to use the results for high-precision maps or construction management. This is where RTK technology comes into play. Combining photogrammetry with RTK overcomes these precision challenges and enables faster acquisition of higher-precision surveying results.

Advances in RTK technology: achieving centimeter-level positioning

RTK (Real-Time Kinematic) is a method that uses satellite positioning (GNSS) technology to obtain centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)) in real time. Specifically, a reference station (base) with known coordinates and a mobile receiver (rover) simultaneously receive GNSS satellite signals, and the base transmits error correction information to the rover to achieve high-precision positioning. Traditionally, conducting RTK surveys required expensive equipment such as dedicated GNSS receivers, radios, and pairs of antennas. However, recent technological advances have miniaturized and reduced the cost of equipment, making RTK benefits more accessible.

The characteristic of RTK is that it provides extremely high positioning accuracy on the order of a few centimeters (cm level accuracy (half-inch accuracy)). General GPS (standalone GNSS) accuracy is said to be on the order of several meters, but RTK dramatically improves this. This precision enhancement has enabled immediate digitization of tasks that require positional accuracy, such as as-built management (post-construction shape verification) in civil engineering and infrastructure inspections. In Japan, the provision of a centimeter-level positioning augmentation service (CLAS) using the quasi-zenith satellite Michibiki has begun, and in mountainous areas where mobile signals do not reach, compatible receivers can achieve high-precision positioning without an internet connection. RTK technology is powerful on its own, but its true value is realized when combined with photogrammetry.

The synergy created by photogrammetry × RTK

The fusion of photogrammetry and RTK brings two major benefits to surveying sites: a dramatic improvement in accuracy, and a dramatic improvement in work efficiency.

On the accuracy front, incorporating RTK-acquired position information into photogrammetry data gives the resulting 3D models and point clouds absolute accuracy. This means that coordinates of arbitrary points on the model nearly match actual geodetic coordinates, eliminating the need for later transformation work or additional control point setup. For example, in drone-based photogrammetry, ensuring accuracy was sometimes difficult unless an RTK-equipped drone was used or ground control points were placed. However, if camera positions or shot locations corrected by RTK can be obtained at the time of photography, much of the pre-flight ground control work can be omitted. Similarly, in ground-based photogrammetry, if the positions of each shooting point are known via RTK during capture, the resulting point cloud data will immediately conform to the site’s surveying coordinate system.

On the efficiency side, simultaneous use of photogrammetry and RTK drastically speeds up the flow from data acquisition on site to deliverables. Traditionally, photos were taken and processed back at the office, and positional calibration had to be done separately by combining GNSS survey data. By combining RTK, which enables real-time positioning, photos taken on site can be immediately linked with positioning information. If needed, provisional point cloud models can be generated on the spot to check for missed shots or uncovered areas. As a result, return trips to the site are reduced and the overall lead time for surveying projects is shortened. Photogrammetry × RTK—achieving both accuracy and efficiency—has attracted attention as the next-generation surveying style.

Simple, high-precision surveying achievable with a smartphone

In recent years, solutions have emerged that make it easy to implement the fusion of photogrammetry and RTK using a smartphone. Smartphones are ideal surveying platforms because they have high-performance cameras and sensors, powerful processors, and intuitive user interfaces. By combining a small RTK-capable GNSS receiver with a smartphone, it can function as a portable “simple surveying instrument” that one person can carry.

For example, using an RTK antenna/receiver that can be attached to a smartphone allows the phone to obtain centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)) in real time. Simply launching a dedicated app and walking while taking photos with the smartphone’s camera records a stream of geo-tagged photos. Since each captured photo is tagged with high-precision coordinates, the point clouds and 3D models generated later by photogrammetric processing will already have accurate positioning information from the start.

Advantages of smartphone-based surveying include:

• Ease of use: Compared with specialized surveying equipment, smartphone surveying is intuitive and can be operated by anyone. Data acquisition is possible by following app instructions without complex settings or advanced knowledge.

• Compact, lightweight equipment: The required hardware is only a smartphone and a palm-sized GNSS receiver. There is no need to carry heavy tripods or large surveying instruments, making it easy to work in confined spaces or at heights.

• Real-time status confirmation: Since positioning status and the shooting coverage can be displayed on the screen, mistakes like “missed shots” or “insufficient data” can be reduced. Data can be checked immediately on site and additional shots taken as necessary.

• Extensibility and updates: Because it operates as a smartphone app, functionality and performance can be improved through software updates. It can flexibly accommodate future technological advances such as integration with new sensors or implementation of AI analysis features.

With these characteristics, a smartphone alone enables the entire cycle of “measure” and “draw” to be completed on site.

Visualizing the site with point cloud scanning

Point cloud data obtained through photogrammetry is a powerful means of visualizing site conditions. A point cloud is a collection of many points that make up the surface of an object, and each point includes 3D coordinates and color information. Point clouds that were traditionally obtained with specialized equipment like laser scanners can now be generated from photographs thanks to advances in photogrammetry.

With smartphone + RTK point cloud scanning, for example, it is possible to collect data by walking and continuously taking photos targeting structures up to about 50-60 m (164.0-196.9 ft) away. The vast number of photos collected are processed in the cloud or on the device and reconstructed into colored, high-precision point cloud models. Because RTK corrects positions, the generated point cloud already aligns with geodetic coordinates, greatly reducing subsequent integration and correction work. With this method, wide roads or development sites can be scanned in a short time (a few minutes), and distances, areas, and volumes can be freely measured from the resulting point cloud, as well as cross-sections created for analysis.

Moreover, if point cloud data are acquired in accordance with the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management guidelines, that data can be submitted as official inspection deliverables. Traditionally, as-built management required manual checks and on-site inspections, but with accuracy-assured point clouds, digital inspections become possible. In this way, photogrammetry and RTK point cloud scanning enable a near complete digital copy of the site, allowing detailed review in the office afterwards.

Overlaying design and site with AR technology

AR (augmented reality) technology that leverages survey data has become far more practical through the combination of photogrammetry × RTK. By viewing the site through a smartphone or tablet screen and overlaying digital drawings or models on that view, design plans and actual site conditions can be compared intuitively. What may seem like mere AR display depends critically on RTK’s high-precision alignment.

Conventional smartphone AR estimates position with the built-in GPS and sensors, which can cause the virtual overlay to drift over time. However, with an RTK-corrected smartphone, displayed 3D models and design lines can remain correctly aligned to real-world coordinates. For example, on a road construction site, overlaying the completed design and current topography in AR makes it immediately obvious whether embankment or cutting is being executed as designed. With drift-free AR, an as-built heatmap (a map showing differences from design in color) can be shared on site with all stakeholders, preventing rework caused by misunderstandings.

AR is also powerful for construction guidance and inspection. In pile-driving work, pile heads must be placed at positions specified in the design; using RTK-capable smartphone AR guidance can navigate workers to pile-driving points so even inexperienced workers can accurately locate pile positions. Similarly, if the positions of buried utilities are recorded by point cloud scanning in advance, smartphone AR can project underground pipe locations transparently during subsequent excavation, helping prevent accidental damage by heavy machinery. Combining photogrammetry-derived data with AR has made site visualization and improvements in construction quality more accessible.

Data sharing and efficiency through cloud integration

Cloud integration also plays a key role in photogrammetry × RTK solutions. Large volumes of photos and generated point cloud models obtained on site traditionally had to be processed on a local high-performance PC, and result files distributed to stakeholders. Modern systems, however, allow one-tap uploads from smartphone apps to the cloud for automated processing and analysis.

Because 3D model generation and various computations are performed in the cloud, users on site can significantly reduce post-processing work by simply doing the shooting. Furthermore, deliverables uploaded to the cloud can be shared instantly via the web. For example, when a surveying company technician acquires a point cloud on site and syncs it to the cloud, supervisors or clients in the office can immediately access and check that data. Without installing dedicated software or preparing a high-performance PC, anyone with a browser can check current conditions in a 3D viewer and take measurements or leave comments as needed.

This cloud integration smooths collaboration between site and office and is making real-time construction management and remote inspections practical. Data stored securely in the cloud also reduces the risks associated with device loss and the burden of backups, and makes it easier to retrieve past data for analyzing long-term changes. Photogrammetry × RTK integrated with the cloud is not just a means of data acquisition but a comprehensive DX solution that includes post-acquisition utilization.

The dawn of a new surveying era: a future where everyone has their own surveying instrument

The fusion of photogrammetry and RTK is paving the way for a future in which not only specialist surveyors but anyone on site can handle high-precision surveying data. Surveying used to be performed with specialized instruments like total stations and levels handled by skilled technicians. But now, with a smartphone and a small RTK receiver as a “one-per-person” surveying tool, individuals can measure as needed whenever necessary.

This trend is accelerating as part of construction DX (digital transformation), contributing to productivity improvements and workstyle reforms on site. With a personal surveying device, one can quickly measure current conditions during a break in work, instantly share them to the cloud, and share information with stakeholders as a matter of routine. Because data acquisition and decision-making can be done autonomously without waiting for a specialist surveying team, project decisions can be made more quickly. Municipalities are also beginning trials in which staff use tablets or smartphones to inspect infrastructure and manage and analyze that data in the cloud. In disaster sites, there are reported cases where staff themselves quickly measured and modeled collapsed areas in a short time and used the results on the same day for damage assessment and recovery planning.

Thus, the new era of surveying is one in which anyone can be both a collector and a user of surveying data. At the center of this is the fusion of photogrammetry and RTK technologies, and the familiar device of the smartphone maximizes that potential.

Conclusion: Realize a field revolution with photogrammetry × RTK

The latest technologies combining photogrammetry and RTK are bringing unprecedented efficiency and accuracy to construction and civil engineering sites. By digitizing site conditions into 3D at speeds previously unimaginable and advancing construction while sharing information with all stakeholders, waste-free, safe, and secure site management becomes possible. A field revolution that can rightly be called a new era in surveying has begun.

One notable solution in this space is LRTK. LRTK is a simple surveying system that leverages smartphones; by fusing photogrammetry and RTK it enables anyone to easily achieve centimeter-level surveying (cm level accuracy (half-inch accuracy)). With a small GNSS receiver that attaches to a smartphone and a dedicated app, it provides an all-in-one package of features such as point cloud scanning, AR display, and cloud synchronization, and has already been adopted by municipalities and companies. Using technologies like LRTK not only dramatically streamlines surveying tasks that used to require manpower and time, but also directly drives DX initiatives on site.

The world of surveying is changing dramatically right now. By adopting the new method of photogrammetry × RTK and leveraging the latest technologies, why not bring innovation to your company’s construction management and infrastructure maintenance? LRTK, which enables high-precision, instant surveying with a smartphone, will strongly support that first step. Experience the new-era surveying style on site and get ahead of the future standard.