Is point cloud measurement possible without LiDAR? The true capability of RTK positioning

Table of contents

• The capabilities and limits of smartphone-mounted LiDAR

• The alternative of photogrammetry

• What is RTK positioning? Centimeter-level position information

• How RTK changes smartphone point cloud measurement

• Field use expanded by simple surveying

• LRTK: 3D surveying anyone can do

• FAQ

The capabilities and limits of smartphone-mounted LiDAR

Recently, I've heard people ask, "Is a LiDAR-equipped smartphone like the iPhone Pro necessary for 3D point cloud measurement?" Indeed, the latest high-performance smartphones include compact LiDAR sensors, enabling easy 3D scanning with a familiar device. LiDAR (Light Detection and Ranging) is a technology that emits laser light and rapidly measures the distance to targets, and even on smartphones it can acquire depth information of spaces to capture surrounding shapes as point cloud data. As a result, a major advantage is that you can scan objects or rooms and create 3D models using only a handheld smartphone, without dedicated surveying equipment. In this article, we will explain in detail methods for measuring point clouds without LiDAR and the true value that high-precision RTK positioning brings.

In practice, smartphone 3D scanning apps make it easy to measure room dimensions or digitize physical models, and applications have expanded among general users.

However, built-in smartphone LiDAR has clear limitations. First, the acquired point cloud is fundamentally in the smartphone’s local relative coordinates, not in global coordinates based on satellite positioning. For example, even if you scan the interior of a room, that point cloud data will tell you relative dimensions inside the building but not the location on a map or allow precise alignment with other survey data. Second, smartphone LiDAR scans tend to suffer from accuracy distortion (drift) over wide areas. When you scan long distances while walking, small errors can accumulate and cause the floor or ground to appear warped. In addition, smartphone LiDAR measurement distance is limited to on the order of a few meters, and the density and accuracy of acquired point clouds do not match those of professional laser scanners, limiting the reproduction of fine surface details. For outdoor wide areas or large structures, targets may fall outside the sensor range. Furthermore, under strong direct sunlight the LiDAR sensor’s accuracy can degrade, making outdoor use sensitive to environmental conditions. Thus, while convenient, smartphone LiDAR alone cannot cover all use cases and has accuracy-related challenges.

The alternative of photogrammetry

Even without LiDAR, you can create 3D point clouds by other methods. A representative technique is photogrammetry. Photogrammetry reconstructs the three-dimensional shape of an object from multiple photographic images; by importing photos taken with drones or cameras into dedicated software, you can generate point clouds and 3D models. Nowadays, smartphones can capture high-resolution photos and videos, so even without special sensors there is potential to obtain sufficiently detailed point cloud data. In fact, 3D modeling from site photos has begun to be used in construction and civil engineering.

The advantage of photogrammetry is that you can create 3D models with an ordinary camera. With a smartphone anyone can easily shoot, so you can record site conditions and later create 3D representations without preparing specialized equipment. Also, point clouds generated from color photos are intuitive and easy to interpret because they are colorized. On the other hand, challenges include the scale (dimensions) and positional accuracy of the resulting 3D models and point clouds. Models generated by photogrammetry determine shape from the relative positions among the source photos. Therefore, while the shape can be realistically reproduced, the real-world size and coordinates remain unclear. For example, a point cloud model of a building generated from photos may have the correct shape but, without proper references, a real 10 m object could be represented as about 9 m in the model. Also, without embedded coordinate information, you cannot place the model on a map or overlay it with other survey data. To obtain accurate dimensions, you must scale the model using measured lengths on site or set several known coordinate values (control points) to adjust it. Without such additional work, 3D data obtained by photogrammetry alone is difficult to use for practical measurements or design comparisons. Conversely, if you provide accurate reference scales or coordinates, photogrammetry results can be fully utilized in surveying work. In fact, methods such as equipping drones with high-precision GNSS to create topographic maps from aerial photos are already common. Similarly, if ground-based smartphone photos are linked with accurate position information, high-precision point cloud measurement can be achieved even without LiDAR.

What is RTK positioning? Centimeter-level position information

So how can we compensate for the uncertainties in scale and position that are weaknesses of photogrammetry and smartphone LiDAR? Enter RTK positioning. RTK (Real Time Kinematic) positioning is a technology that enhances satellite positioning such as GPS in real time to achieve high precision. Typical smartphone GPS has errors on the order of meters, but RTK uses correction information from a reference station to reduce errors to within a few centimeters. RTK-GNSS receivers have long been used in surveying, and recent miniaturization and cost reductions have produced pocket-sized receivers and devices that can interface with smartphones.

Here is a simple explanation of how RTK works. One unit acts as a fixed reference station with a known accurate position, and another is a rover used while moving. The reference station calculates the GPS signal errors it receives at its location and sends that correction data to the rover via radio or network. The rover then uses that correction to determine its own position with centimeter precision. In Japan, for example, RTK positioning is accessible using services like the Geospatial Information Authority of Japan’s electronic reference point network or CLAS (centimeter-class correction information) distributed from QZSS (Michibiki). In short, with RTK a smartphone can determine "where it is right now" with an error of only a few centimeters. Of course, high-precision positioning requires a clear view of the sky to receive sufficient satellite signals, but in open sites centimeter-class positioning is stable.

(centimeter-level position information (cm level accuracy (half-inch accuracy)))

How RTK changes smartphone point cloud measurement

Combining RTK’s high-precision positioning with smartphone 3D scanning resolves the issues discussed above at once. If RTK position information is used when taking photos with a smartphone, each photo will be linked to an accurate capture coordinate. When creating a point cloud from multiple photos, because the camera positions are already known precisely, the 3D reconstruction can be performed with the correct scale and coordinates. As a result, the resulting point cloud data is aligned from the start with real-world survey coordinates, making it straightforward to measure distances and areas or compare with design data.

For example, the steps for photogrammetry using RTK are as follows.

• Use a smartphone connected to an RTK receiver to photograph the target from various angles

• Each photo automatically records capture position coordinates with centimeter-level accuracy

• Reconstruct a 3D point cloud from the photo set using dedicated software (reconstructed at real-world scale based on position information)

• Use the completed point cloud directly for drawing comparisons or distance/area measurements

Additionally, combining RTK with smartphone LiDAR scanning can help prevent positional drift and distortion during scanning. Normally, walking while performing a LiDAR scan accumulates slight ego-motion estimation errors that can bend the point cloud. But if you record while continuously correcting the device’s absolute position with RTK, you can significantly suppress drift that makes floors wave or walls lean. For example, when scanning a large floor area, using RTK will allow the floor to be recorded as properly level and reflect true elevation differences. In other words, RTK’s high-precision positional information acts as a virtual "moving reference point," allowing the smartphone to continue scanning the entire space correctly even while moving.

Furthermore, RTK enables point cloud measurement even with smartphones that lack LiDAR. Even without LiDAR, smartphone camera + IMU (inertial sensor) AR technologies can capture feature points of the surroundings to acquire a simple point cloud. When RTK supplements position, camera-only 3D scans that formerly had insufficient accuracy can be elevated to a practical level. In sum, adding a foundation of high-precision position information brings smartphone-based point cloud acquisition close to practical use regardless of the presence or absence of sensors.

Field use expanded by simple surveying

When RTK-enabled smartphone point cloud measurement becomes a reality, its use cases expand greatly. For small-scale earthworks or surveys around structures, where previously you would have to call in specialized surveying equipment or a team, site personnel can quickly perform surveys themselves with just a smartphone. From the acquired point cloud data you can later calculate earth volumes or create cross-sections. In progress management, regularly scanning a site and recording construction form in 3D enables more intuitive and detailed difference detection than traditional photo planar comparisons.

Also, because acquired point clouds always include coordinate information, overlaying with design 3D models or existing map data is easy. If you overlay a site-scanned point cloud with a planned BIM model in the cloud, you can check discrepancies between as-built and design on the spot, helping prevent rework and improve quality control.

In disaster response, pocket-sized devices proved powerful where large equipment could not be brought in. Even in hazardous areas where people cannot enter, lightweight smartphone surveying allows safe situational awareness. In one earthquake disaster, despite disrupted communications infrastructure, pocket-sized RTK devices were used to record the damage in 3D and helped rapid restoration planning.

From infrastructure inspection to civil works management, making simple 3D surveying a tool anyone can use will further accelerate site digitalization.

LRTK: 3D surveying anyone can do

A solution that makes this new surveying experience—combining smartphones and RTK—easily achievable is LRTK. LRTK transforms a smartphone or tablet into a centimeter-level surveying instrument by attaching a compact RTK-GNSS receiver. Its weight is approximately 125 g, and thickness is 13 mm (0.51 in), making it extremely compact with a built-in battery. Its pocketable size and the ease of taking it out and using it when needed are attractive features.

A smartphone fitted with LRTK functions as an all-purpose surveying device. With the press of a button you can measure and record the coordinate of your current location, and you can instantly measure the distance between two points as a substitute for a tape measure. Naturally, the point cloud scanning described in this article can be completed using only a smartphone and LRTK. The acquired 3D point cloud data already contains global coordinates, so there is no need for later alignment; you can upload to the cloud for immediate sharing and analysis. High-precision photos taken on site are linked and saved to their corresponding positions on the point cloud, enabling integrated management of 3D data and 2D records.

Designed for intuitive operation even without specialized knowledge, anyone familiar with smartphones can quickly become proficient. The price is also much more accessible than traditional surveying equipment, making it truly a solution suited to an era of "one device per person." In fact, many construction managers are already beginning to use LRTK on site, and it is attracting attention as a new surveying style that combines ease of use and high precision. You don’t need an expensive LiDAR-equipped model. By combining LRTK with your smartphone, from tomorrow you too can perform point cloud measurement and simple surveying as you wish.

FAQ

Q: Can I do 3D scanning with a smartphone that doesn’t have LiDAR? A: Yes. If you augment with precise position information via RTK, such as with LRTK, you can obtain point cloud data using only a camera. Even without LiDAR, you can reconstruct high-precision 3D models from multiple photos, and real-time AR scanning can achieve practical accuracy with positional correction.

Q: What’s the difference between scanning with a LiDAR-equipped smartphone and scanning combined with RTK? A: Scanning with only a smartphone’s built-in LiDAR is attractive for its simplicity—you can easily capture shapes on the spot with a single device. However, as noted earlier, the resulting point cloud remains local shape data with limitations in the reliability of coordinates and scale. When combined with RTK, each acquired point in the point cloud is assigned accurate position coordinates, and data can be joined across wide areas without distortion, yielding survey-grade results ready for practical use. Also, point clouds obtained solely with LiDAR require alignment when comparing with other drawings or maps; with RTK, data is obtained in the correct coordinate system from the start, reducing post-processing effort. In short, if LiDAR alone is a tool for "capturing shape," the combination with RTK makes it a tool for "measuring."

Q: Is accuracy sufficient compared to conventional 3D scanners or surveying equipment? A: It depends on the application, but with proper operation centimeter-level accuracy can be expected. While you may not obtain the same high-density point clouds as professional laser scanners, the accuracy is sufficient to determine the position and dimensions of features. There are reports that point clouds obtained by RTK-enabled photogrammetry achieved accuracy comparable to laser scanners for hard ground surfaces. For specialized cases requiring millimeter accuracy or detection of fine cracks, dedicated laser scanners still have the advantage, but for many surveying tasks smartphone surveying provides adequate accuracy.

Q: Do I need specialized knowledge or qualifications to use RTK? A: No, no special qualifications are required, and operations are completed via smartphone apps, making it simple. There is setup to receive satellite correction information from an RTK receiver, but once configured it performs positioning automatically. Even users without surveying experience can obtain high-precision positions by following the app instructions and pressing the positioning button.

Q: What kinds of sites are smartphone surveys useful for? A: In addition to construction and civil engineering, they are useful for equipment inspections and disaster response. Examples include recording daily changes in as-built condition with point clouds for form management, measuring topography before and after excavation to calculate earth volumes, and recording buried utilities in 3D before backfilling so that hidden elements can be accurately located later. In disaster sites, quickly obtaining 3D data of damage supports restoration planning. Because lightweight smartphone surveying can be brought into areas difficult for people to enter, it enables safe acquisition of topographic and structural information.

Q: Do I need a specific model like an iPhone to use it? A: Currently LRTK supports iOS devices such as iPhone and iPad (※ Android support will be announced if/when available). It can be used regardless of whether the device has LiDAR, so you can turn your existing smartphone into a high-precision surveying instrument.

Q: Can high-precision positioning be achieved in remote mountainous areas without network coverage? A: Yes. Even without Internet access, you can achieve RTK positioning by receiving correction information distributed from QZSS (Michibiki) such as CLAS. In disaster areas where base station radio cannot reach, satellites overhead can provide real-time accuracy enhancement, enabling stable positioning. Of course, you can also set up and operate your own local reference station on site. RTK’s strength is that various methods can be used to maintain high-precision positioning depending on the situation.