Introductory Guide to Point Cloud Surveying with High-Precision Positioning: Easy 3D Measurement with a Smartphone

Table of Contents

• What is high-precision positioning?

• What is point cloud surveying?

• The expanding possibilities of 3D measurement with a smartphone

• Benefits of combining high-precision positioning and point cloud surveying

• Recommendation: simple surveying with LRTK

• FAQ

What is high-precision positioning?

High-precision positioning is a technology that determines locations with centimeter-level errors by using satellite positioning systems (GNSS) and the like. The GPS built into ordinary smartphones or car navigation systems generally has positioning errors of about 5-10 m (16.4-32.8 ft). This is sufficient for everyday use but inadequate for civil engineering surveying or construction management. For example, a displacement of several meters is unacceptable when staking out road boundaries or building positions. That is where high-precision positioning technologies such as Real-Time Kinematic (RTK) positioning come in.

RTK positioning is a method that computes centimeter-level positions in real time by correcting satellite signal errors between a reference station (a receiver at a known accurate position) and a rover (the receiver at the point to be surveyed). In this method, correction information is sent from the reference station to the rover to cancel out error factors in the satellite signal (such as atmospheric effects and clock errors). As a result, coordinates of a precision unobtainable with standalone GPS can be acquired. In Japan, high-precision positioning can be easily realized by utilizing systems such as the Geospatial Information Authority’s Continuously Operating Reference Stations and the Quasi-Zenith Satellite System “Michibiki,” which provides CLAS (Centimeter-level Augmentation Service). By using these systems, smartphones or small GNSS receivers can achieve positioning within a few centimeters without installing a dedicated base station.

In short, high-precision positioning is a technology to “determine the coordinates of a targeted point almost without error,” and traditionally expensive surveying equipment was required. However, in recent years affordable, compact high-precision GNSS terminals and systems that operate in conjunction with smartphones have appeared, making the technology increasingly accessible. This allows not only specialized technicians but a wide range of people at civil engineering and construction sites to obtain high-precision positional information. Furthermore, high-precision positioning is used as an elemental technology in ICT construction for bulldozer and excavator machine guidance and machine control. Enabling everyone on site to use smartphone-level positioning accuracy comparable to these technologies—which automatically control heavy machinery position and blade height to the centimeter—represents a breakthrough for DX (digital transformation) in the construction industry.

What is point cloud surveying?

Point cloud surveying is a method of acquiring surrounding structures and terrain as a collection of numerous points (point cloud data) to record and measure shapes in three dimensions. Traditional surveying measured coordinates and elevations point by point with instruments such as total stations and levels, and connected those measurements to produce drawings. With point cloud surveying, laser scanners (LiDAR) or photogrammetry can acquire millions of survey points at once. This allows detailed 3D data of the ground surface and structures to be recorded, dramatically improving surveying efficiency.

Point cloud data is a set where each point has (X, Y, Z) coordinate information and appears like a cloud of points (a point cloud). From this data, you can calculate distances, areas, and volumes, create longitudinal and cross sections, and compare with design models—enabling various analyses. For example, in cut-and-fill quantity calculations and as-built management, creating a current terrain model from point clouds allows fast and accurate quantity estimation. Point cloud surveying is also used for recording cultural properties and measuring displacements of tunnels and bridges—tasks that are difficult to perform manually.

Recently, acquiring point clouds using UAV (drone)-mounted LiDAR and photogrammetry software has become common, making large-scale terrain surveys more efficient. On the other hand, such dedicated equipment and software are expensive and require specialized knowledge to operate. While the benefits of point cloud surveying are substantial, historically it has been limited to specialists or sites with sufficient budgets. Therefore, methods for conducting 3D surveys more easily and at lower cost have attracted attention in recent years. With the promotion of ICT in construction represented by i-Construction, the use of drone photogrammetry and laser scanners is encouraged. In that context, a new option—“point cloud surveying with a smartphone”—is emerging. This low-cost, easy method is expected to see increasing demand.

The expanding possibilities of 3D measurement with a smartphone

Thanks to improvements in smartphone and tablet performance, an era has arrived in which anyone can easily perform 3D measurement. Particularly noteworthy are measurement technologies that utilize built-in smartphone sensors and cameras. Some of the latest smartphones include accelerometers and gyroscopes as well as depth sensors (LiDAR) that support AR technology. For example, certain models of Apple’s iPhone and iPad have built-in LiDAR sensors, and with dedicated apps you can scan the surrounding space to obtain point cloud data. This makes 3D measurements that previously required dedicated laser scanners feasible with a single smartphone.

Another major attraction of smartphone 3D measurement is its intuitive operation. By pointing the camera at the real space shown on the screen and walking around, point clouds are generated automatically. No complicated equipment setup or specialized operation is required, and site conditions can be digitized in a short time—so more field personnel are performing measurements themselves. Additionally, smartphones are tools people carry at all times, so their mobility allows immediate measurement whenever needed. Narrow interiors and inaccessible areas can be recorded simply by pointing a smartphone, making the technology useful for inspections and disaster site documentation. Such easy 3D measurement with smartphones will continue to evolve and become a foundation supporting DX (digital transformation) in construction.

However, point clouds obtained by a smartphone alone have limitations in terms of positioning (location information) accuracy. Point clouds from smartphone LiDAR or cameras are aligned relatively using the device’s IMU sensors and vision algorithms. Therefore, the generated point clouds are not tied to real-world coordinate systems (latitude/longitude or planar coordinates), and their scale (dimensions) precision is not exact. While they can be used for simple dimension measurements, they are not directly suitable for applications that require strict position or elevation results as surveying deliverables. What is needed here is an approach that combines the point cloud captured by a smartphone with information from high-precision positioning.

Benefits of combining high-precision positioning and point cloud surveying

Combining the convenience of smartphones and the efficiency of point cloud surveying with the reliability of high-precision positioning yields significant advantages in surveying. This approach enables high-precision point cloud surveying with light equipment operated by a single person. Specific benefits are listed below.

• Reduction in personnel and time: Traditional total station surveying requires setting up heavy equipment and usually two-person teams to observe each point. With high-precision GNSS receivers and a smartphone, one person can walk around the site and acquire 3D data over a wide area. Preparation and teardown times are reduced, and the overall surveying time decreases substantially.

• Efficient data acquisition: Point cloud scanning captures a large number of points at once, allowing dimensions or coordinates at any location to be measured later. There is less “missed” data and fewer returns for re-surveying. Especially for complex terrain or structures, recording the whole site as a point cloud enables free analysis of necessary sections and details back in the office.

• Reliability through high positioning accuracy: Introducing high-precision positioning allows absolute coordinates (latitude, longitude, elevation) to be assigned to acquired point clouds. This makes it possible to directly compare point cloud data with existing survey coordinate systems and design drawings, smoothing as-built management and quality checks. For example, in road construction, accurate verification of discrepancies between the design model and as-built can be performed with high-precision point cloud data.

• Improved safety: Remote measurement enables data collection from safe locations, reducing risk in dangerous or unstable sites. It also lowers dangers for workers when surveying at heights or on slopes.

• Immediate sharing and decision-making: Digitally acquired 3D data can be displayed and reviewed on a tablet at the site. Uploading to the cloud allows the office or remote colleagues to instantly share the site status. With high-precision positioning attached to the data, reliable decisions can be made without being on site, speeding up decision-making.

Thus, “high-precision point cloud surveying,” which combines high-precision positioning and smartphone point cloud measurement, is a groundbreaking method that overturns conventional wisdom. Without specialized equipment or advanced skills, high-quality 3D surveying results can be obtained, making this approach attractive to a wide range of users from civil engineering contractors to local governments.

Recommendation: simple surveying with LRTK

One concrete solution that realizes the fusion of high-precision positioning and smartphones described above is LRTK. LRTK is a system consisting of a small high-precision GNSS receiver that can be attached to a smartphone and a dedicated app, and it is gaining attention as a simple surveying tool that anyone can handle. By simply attaching a smartphone-sized device weighing about 165 g, roughly 1 cm (0.4 in) thick, you can achieve centimeter-level positioning in real time as soon as you arrive at the site. The device has an internal battery and operates for about 6 hours, so it is reliable even for long work periods (it can also be charged from an external battery via USB Type-C). It can also be mounted on a monopod or surveying pole for stable positioning when necessary. Due to the specifications of the LRTK terminal, positioning accuracy of about ±2 cm (±0.8 in) in planimetric position and ±3 cm (±1.2 in) in elevation is achievable, which rivals professional surveying instruments. For example, it supports CLAS signals provided by Japan’s Quasi-Zenith Satellite “Michibiki” and network RTK via the internet (Ntrip), enabling stable high-precision positioning even in mountainous areas where mobile signals may not reach.

What makes LRTK superior is not only its high-precision positioning but also the one-stop availability of acquired point clouds and AR functions. With just a smartphone, positioning, measurement, recording, and sharing can be completed, dramatically simplifying site workflows. For instance, using an LRTK system you can directly attach latitude, longitude, and elevation information to point clouds scanned with an iPhone’s camera and LiDAR. As a result, the point cloud can be used immediately within the survey coordinate system without subsequent coordinate alignment. Additionally, AR functions allow projection of design models into the real world for stakeout support. The fact that these tasks can be performed intuitively by field personnel rather than specialized operators is precisely what makes it simple surveying.

Now let’s look at the basic workflow for surveying using a smartphone + LRTK.

• Prepare high-precision positioning: Attach the LRTK receiver to the smartphone, power it on, and receive satellite position information. Configure correction information (network RTK or CLAS) to enable centimeter-level positioning.

• Conduct point cloud scanning: Start LiDAR scanning (or photogrammetry) with the dedicated app and walk around the area to be measured while holding the smartphone. A 3D point cloud is displayed on the smartphone screen in real time so you can confirm the measurement progress.

• Check data on site: While scanning, view the point cloud model from various angles to check for missed areas. Add scans as needed to supplement the on-site data.

• Save and share data: After measurement, the acquired point cloud data is saved on the smartphone (with latitude, longitude, and elevation attached). Uploading to the cloud allows detailed analysis and drafting on office PCs and sharing with stakeholders.

Advanced general contractors and surveying companies have already begun using smartphone surveying with LRTK. This flexible surveying style that does not rely on dedicated equipment will be powerful for small sites, emergency inspections, and disaster response. If you want to try “point cloud surveying with high-precision positioning” in your organization, it is recommended to conduct a trial introduction of a system like LRTK to experience how easily measuring and surveying with a smartphone can be.

FAQ

Q1. Is special equipment required for high-precision positioning? A. Yes. To achieve centimeter-level high-precision positioning, the GPS built into ordinary smartphones is not enough. Dedicated high-precision GNSS receivers that support RTK, or devices that support Michibiki’s CLAS signals, are required. However, small and affordable GNSS receivers have emerged recently, and they can be easily used by connecting to smartphones via Bluetooth or cable.

Q2. Can point cloud surveying be done with smartphones that do not have LiDAR? A. Yes. Point clouds can be generated using photogrammetry even on smartphones without LiDAR. There are apps and software that create 3D models and point clouds by photographing an object from multiple angles with a smartphone camera. However, photogrammetry can take longer to process and may not achieve sufficient accuracy depending on the target, so LiDAR-equipped models that provide real-time on-site point clouds are more convenient.

Q3. What level of accuracy or error can be expected for point cloud data? A. The accuracy of point cloud data varies depending on the equipment and methods used. High-quality laser scanners can produce point clouds with millimeter-level accuracy, whereas smartphone LiDAR may produce errors on the order of several centimeters depending on environmental conditions. However, combining with high-precision positioning can reduce positional errors to within a few centimeters, making the data practical for surveying purposes. The important point is whether the achieved accuracy meets the measurement objectives; the smartphone point cloud + high-precision GNSS combination provides acceptable accuracy for many site applications.

Q4. Is post-processing of site-acquired data difficult? A. Point cloud data acquired by smartphones can be visualized and edited with dedicated apps or PC software. Post-processing tasks include removing unnecessary points, coordinate system transformation, and extracting cross sections, but recent tools have improved usability so basic processing can be done without special skills. Using cloud services allows heavy point cloud data to be shared over the internet for smooth collaboration. LRTK systems also offer cloud integration features to instantly share scanned on-site data with the office.

Q5. How much does it cost to introduce high-precision point cloud surveying? A. Introduction costs vary depending on the equipment configuration. Traditional 3D laser scanners can cost several million yen or more, but a smartphone with a small GNSS receiver can be started at a fraction of that cost. Specific prices depend on products and services, but many organizations first trial small kits to verify effectiveness before full deployment. It is important to consider not only initial investment but also labor and time cost savings achieved by the method. If low-cost, high-precision surveying can be realized, site productivity will improve.

Q6. Can smartphone surveying replace traditional instruments such as total stations? A. Surveying with smartphones and high-precision GNSS greatly increases work efficiency in many cases, but it does not completely eliminate the need for traditional instruments. For example, GNSS positioning relies on satellite signals and can be unstable inside tunnels or in the shadow of tall buildings. Also, tasks requiring millimeter-level precision such as precise control point surveys or creating legally binding survey maps still favor total stations and other precision instruments. However, for general terrain surveying, as-built management, and site condition surveys, smartphone surveying increasingly yields sufficient results. By choosing between traditional methods and smartphone surveying according to site conditions, each approach’s strengths can be leveraged for efficient surveying.