Everyone Can Be a Surveyor with Photogrammetry! High-Precision 3D Point Cloud Measurement Starting with Smartphone RTK

(Introduction) Surveying work is indispensable on construction sites and for infrastructure management. Until now, it was often necessary to hire licensed surveyors or specialist firms, which involved time and cost. However, in recent years, advances in photographic surveying technology known as photogrammetry have made an era possible in which anyone can acquire high-precision 3D point cloud data with a smartphone. In particular, by combining a smartphone with RTK (real-time kinematic)—so-called “smartphone RTK”—it has become possible to balance the ease of use for non-licensed personnel with surveying accuracy approaching that of traditional methods. This article clearly explains the basics of acquiring point clouds using photogrammetry, how smartphone RTK enables high precision, and practical on-site use cases. Let us look at the appeal and implementation benefits of photogrammetry + RTK as a promising new on-site tool.

What is photogrammetry? Basics of 3D point cloud data created from photos

Photogrammetry is, literally, a technique that reconstructs the three-dimensional shape of an object using photographic images. By photographing the target from many angles with digital cameras, smartphones, or drone-mounted cameras, and processing those images with dedicated analysis software, you can generate high-density point cloud data and 3D models. The computer matches feature points captured in the photos and uses parallax to calculate the position of each point (X, Y, Z coordinates), and a defining feature is the ability to digitize object shapes in detail down to the millimeter level (mm level; 0.04 in).

For example, scanning the exterior of a building with photogrammetry can produce a point cloud model that includes fine surface irregularities and color information. Because photo-derived point clouds have RGB color, they can reproduce not only shape but also appearance very faithfully. Photogrammetry can be used across a wide range of scales, from large-scale terrain surveys by drone to measurements of familiar structures using a smartphone. It is revolutionary that 3D point clouds that previously required expensive laser scanners (LiDAR) can now be obtained at low cost using only a handheld camera.

Of course, 3D reconstruction from photos requires computational processing, so it is inferior to laser scanners in real-time performance. However, recent advances in software and hardware have shortened processing times, and apps that allow previewing point cloud generation on tablets and smartphones have appeared. The required equipment is simple—just a camera and software—and as long as you can take photos, you can create 3D data without special surveying skills, making photogrammetry a technology of interest for on-site DX (digital transformation).

What is smartphone RTK? Centimeter-level positioning achieved with a smartphone

Point cloud data obtained by photogrammetry can have high relative accuracy within the object, but it faces the problem that absolute position coordinates are unknown. Simply put, to align the finished 3D model with a map or design coordinate system, scale adjustments and positioning are necessary. Traditionally, survey control points (known-coordinate points) were placed on site, photos were taken to include those points, and the model was registered afterwards.

This is where the powerful high-precision positioning technology called RTK (real-time kinematic) comes into play. RTK-GNSS works by simultaneously receiving signals from GNSS satellites at a base station (a receiver placed at a known point) and a rover (a receiver connected to a smartphone, etc.), and the base station transmits the error information to the rover in real time to correct it, improving position accuracy to the order of centimeters. While ordinary GPS positioning can have errors on the order of several meters, using RTK allows you to measure the current position with centimeter-level accuracy (cm level accuracy (half-inch accuracy)).

Recently, this RTK technology has become easy to use with smartphones. Compact RTK-GNSS receivers that attach externally to smartphones have appeared from various manufacturers; by connecting via Bluetooth or a dedicated cable, a smartphone can support centimeter-level positioning. In effect, the smartphone becomes a high-precision surveying instrument—because these devices are lower cost and smaller than dedicated equipment, it is realistic for all field staff to carry one device each. Furthermore, in Japan the development of network RTK (correction information distribution services) using systems such as the Geospatial Information Authority’s reference station network has progressed, so within communications coverage you can perform centimeter-class positioning easily without providing your own base station.

With this “smartphone RTK,” it has become possible to attach real-time high-precision absolute coordinates to point cloud data obtained by photogrammetry. You can tag each photographed image with coordinates obtained by smartphone RTK, or directly overlay RTK coordinates onto a smartphone LiDAR scan so that the generated point cloud is obtained already aligned to a public coordinate system. As a result, post-processing registration work can be greatly simplified, and the acquired data can be immediately overlaid on maps, CAD drawings, or BIM/CIM models for practical use. Photogrammetry × RTK is a powerful combination that allows 3D point clouds obtained in the field to be placed directly into surveying coordinates.

Combining ease and high precision: surveying that anyone can do

The advantage of combining a smartphone with photogrammetry and RTK is the balance of “ease of use” and “high precision.” Traditionally, performing precise 3D surveys required learning how to handle expensive equipment and deploying a specialized surveying team—sometimes taking half a day or more. In contrast, photogrammetry using a smartphone and camera offers the simplicity of being able to record an entire site in 3D with a single smartphone. The only special equipment needed is a camera and a GNSS receiver; the operation is intuitive, so even beginners can use it, and in-house technical staff can perform measurements themselves.

The relatively small initial investment is another important point. For example, conventional terrestrial laser scanners cost several million yen, whereas smartphone-compatible RTK receivers and 3D scanning apps can be obtained for a fraction of that cost. Because staff who do not own expensive surveying instruments—such as local government employees or construction site managers—can use their own smartphones for precise measurements, this leads to in‑house capabilities and reduces dependence on outside surveying firms.

Another major benefit is that this approach can be used without a national surveying license such as that held by surveyors. While officially certified surveying results for public works require involvement by licensed personnel, for everyday tasks such as current-condition assessment or finished-shape confirmation, anyone can collect data using modern tools. In an environment of labor shortages and an aging workforce, being able to measure without waiting for a specialized survey team increases productivity on site.

Of course, some technical proficiency and planning are necessary—don’t rely solely on the equipment. Basic practices like taking photos with sufficient overlap in photogrammetry and ensuring a clear view of the sky for RTK to receive satellites must be observed. Even so, compared with traditional total station surveys or leveling, this method is markedly simpler, and having on-site staff take the lead in measurements is highly valuable. The Ministry of Land, Infrastructure, Transport and Tourism’s push for i-Construction is also a tailwind, and such digital measurement methods are rapidly spreading in construction management and maintenance fields.

Comparison with conventional surveying methods: what’s revolutionary?

So how does measurement by photogrammetry + smartphone RTK compare to conventional surveying? Let’s compare across several aspects.

• Data acquisition range and density: With traditional methods, points are measured one by one manually, so the number of points obtained is limited. For example, in terrain surveys you might record elevation points every several tens of meters (tens of meters (tens of ft)), but photogrammetry can turn every visible location in the photos into point cloud, enabling wide areas to be covered at high density. This reduces omissions and minimizes later worries of “I wish we had measured that point as well…”.

• Work time and efficiency: Manual surveying requires time for equipment setup, tripod placement, and target installation, and can take multiple people half a day to several days. In contrast, photogrammetry measurements completed by photography and smartphone positioning require little on-site shooting time and have automated post-processing. On small sites, one person can complete shooting in tens of minutes, and you can generate and review a point cloud model the same day, realizing a rapid workflow.

• Accuracy and reliability: Traditional methods (total stations and leveling) excel at millimeter- to centimeter-level high precision, but converting to a point cloud is difficult and capturing the overall shape requires many point measurements. With photogrammetry + RTK, the relative accuracy of the point cloud depends on photo resolution and shooting quality, but if performed properly dimensional accuracy of the order of a few millimeters to a few centimeters (a few mm (0.04 in) to a few cm (0.4 in)) can be achieved. In addition, absolute coordinate correction with RTK brings positional accuracy within a few centimeters, so it can meet the 5 cm accuracy (5 cm (2.0 in)) required by finished-shape management guidelines. However, when surveying very large sites at uniformly high precision in one pass, a combination of drone photogrammetry or fixed 3D scanners with RTK may be appropriate—choosing the right tool for the situation is important.

• Safety: Taking measurements on dangerous slopes or down in deep excavations carries risk. With drone or pole-mounted photography you can obtain data without personnel entering hazardous areas, and smartphone measurements can be done from a distance with zoom. The ability to measure without direct approach to the target is a major advantage of digital measurement and contributes to on-site safety management.

• Immediate sharing and utilization: Digitally acquired point cloud data can be shared via the cloud or imported into CAD/BIM software, making downstream use easy. Compared with traditional methods that manage point lists in paper field books, point cloud data allows intuitive understanding of site conditions and enables 3D site review from remote offices.

As described above, photogrammetry + smartphone RTK has many strengths over conventional surveying in terms of data volume, efficiency, and safety. There will still be cases where traditional equipment is used alongside these methods, but the combination’s ability to produce large amounts of high-precision data with relative ease is transformative for on-site measurement.

On-site use cases: from finished-shape management to asset registers

In actual construction and surveying sites, point cloud measurements by photogrammetry + RTK are powerful in a variety of applications. Here are some representative use cases.

• Finished-shape management: Point cloud scanning is valuable for accurately measuring earthworks and structure finished shapes for quality control and quantity calculations. From point clouds obtained by drone or ground photos, you can instantly calculate embankment volumes and slope gradients, significantly reducing labor compared to traditional cross-section surveys. Combining RTK positioning correction further increases the reliability of the measurements and enables efficient production of deliverables that meet the 5 cm accuracy (5 cm (2.0 in)) required by public projects. For example, by placing an RTK receiver at a reference point in advance and photographing the entire embankment with a smartphone to generate a point cloud, you can quickly obtain a finished-shape point cloud model aligned to the Ministry of Land, Infrastructure, Transport and Tourism’s reference coordinate system.

• Current-condition surveys and maintenance: It is also effective for recording and inspecting infrastructure such as roads, rivers, and bridges in 3D. Instead of keeping only drawings and photos, you can store the condition of structures as objective records in point clouds, allowing the positions and sizes of cracks and deformations to be quantified. For local government staff managing regional infrastructure, the ability to scan sites themselves without calling specialist contractors is a major advantage. For example, scanning the underside of a bridge with a smartphone lets you later examine the placement of steel members and deterioration points in detail at a desk, and easily compare past data at the next inspection to detect changes.

• Simple asset registry creation: Photogrammetry + RTK is useful for creating simple registry data of the position and shape of infrastructure assets like street furniture and water/sewer pipes. For instance, if you measure the positions of roadside signs and guardrails using smartphone RTK while photographing them and then create a 3D model from the photo set, you can use it as a coordinate-attached registry. Tasks that used to require staff to measure distances with a tape and plot them on plans can now be completed simply by walking and recording with a smartphone. Once point cloud data are placed on a map, you can overview site conditions in 3D from the office and improve efficiency in maintenance management and repair planning.

Additionally, high-precision point cloud data can be used for comparison with design 3D models. Overlaying the completed point cloud with design data allows automatic color-coded displays of excesses and deficiencies, instant calculation of additional embankment volume, and other advanced analyses. With point cloud data and RTK-based high-precision coordinates, AR (augmented reality) can project designs onto the site for on-the-spot finished-shape checks without special equipment. You can not only measure and record but also directly use measured data for subsequent construction management and inspection. Photogrammetry + RTK is expected to be a key technology for on-site DX with a variety of applications.

On-site implementation benefits: efficiency and DX promotion

As described above, point cloud measurement using photogrammetry and smartphone RTK brings many benefits to the site. Finally, let’s summarize the main advantages of introducing this new technology on site.

• Significant efficiency gains: Because you can start measuring alone as soon as you want, there is no need to arrange a surveying team or wait for their arrival. Tasks that used to wait for surveying staff can now be handled immediately by your own department, speeding up decision-making.

• Labor savings and cost reduction: Reducing outsourcing to specialist firms and enabling surveying that used to require multiple people to be done by one person can mitigate labor shortages and reduce personnel costs. Because smartphone-based equipment is relatively inexpensive, equipping every field staff member can sometimes cost less than a single dedicated device.

• Advanced data utilization: The obtained point cloud data are not just numerical lists but can be handled intuitively as 3D models. Shared on the cloud, site and head office can grasp the situation in real time, and finished-shape checks and quantity calculations can be completed digitally. Accumulated data can be repurposed for future maintenance documentation or BIM/CIM uses, forming a long-term DX foundation.

• Improved safety and quality: Remote measurement of hazardous locations enhances worker safety. Compared with manual measurements, measurement omissions and recording errors are reduced, improving data quality. Thorough point cloud records advance site visualization and raise the precision of quality control.

• Easier skills transfer: Because non-specialist staff and younger employees can use the technology without dependency on experts, it helps mitigate knowledge loss from veteran retirements. Intuitive smartphone operation lowers the bar for training new staff and raises organizational technical capability.

Conclusion: a new era of surveying expanded by smartphone RTK

The combination of photogrammetry—where you can perform high-precision 3D surveying simply by taking photos—and smartphone RTK holds the potential to let anyone become a surveyor. This technology, which overturns conventional expectations, is now a practical means to dramatically improve on-site productivity and data utilization.

In fact, pocket-sized RTK-GNSS receivers that attach to smartphones and dedicated apps—such as solutions dubbed “LRTK”—are beginning to appear. By attaching one to a smartphone and turning it on, you can immediately achieve centimeter-class positioning and perform point cloud scans, stakeout guidance, and AR-based design checks, making it an all-in-one surveying tool. Using such products, a time is near when spatial measurement on site will be commonplace without special equipment or licenses.

The new method of photogrammetry + smartphone RTK is poised to become a trump card for DX in the construction industry and infrastructure management. If you have not yet adopted it at your site, why not take this opportunity to try it out? High-precision 3D point cloud measurement starting with a smartphone and photos will surely help shape the future of your field.