Table of contents

• What RTK positioning is

• Points to consider when choosing an RTK receiver

• Applications to point cloud scanning and photogrammetry

• Indoor positioning and AR utilization

• Benefits of introducing RTK

• Simple surveying with smartphone RTK "LRTK"

• FAQ

What RTK positioning is

RTK positioning (Real-Time Kinematic), which has attracted attention in recent years in construction, surveying, and infrastructure management, is a centimeter-level high-precision positioning technology that uses GNSS (Global Navigation Satellite Systems). Standalone positioning with ordinary GPS or GNSS typically produces errors of several meters to around 10 m, which is insufficient for millimeter-level precision required in construction quality control and surveying. RTK corrects these errors in real time, achieving accuracy within a few centimeters.

RTK positioning uses two receivers simultaneously: a reference station (base) with known accurate coordinates and a mobile station (rover). The reference station calculates error information and sends it to the rover via radio or the Internet, and the rover applies corrections to its own position to achieve higher accuracy. This mechanism cancels satellite signal errors that cannot be corrected by a single receiver, enabling the precise positioning required in actual construction and surveying sites. Combining an RTK-capable receiver with correction information can streamline surveying tasks that were traditionally performed with total stations and enable wide-area surveying to be handled by a single person.

Points to consider when choosing an RTK receiver

There are many models of RTK receivers (high-precision GNSS receivers) with various specifications and features. To select a model that fits your site needs, check the following points.

• Supported GNSS satellite systems: Check which satellite systems the receiver can use. A multi-GNSS receiver that supports GPS, GLONASS, Galileo, BeiDou, and Michibiki (QZSS) increases the number of visible satellites and tends to maintain stable positioning even under obstructions. In Japan, support for the quasi-zenith satellite Michibiki is particularly desirable, as it helps ensure a satellite overhead and contributes to improved accuracy.

• Supported frequency bands: Confirm whether it supports multiple frequencies such as L1/L2/L5. Dual-frequency (L1+L2) receivers can correct ionospheric errors, improving initialization time and positioning accuracy compared to single-frequency receivers. Recently, triple-frequency receivers that include L5 have appeared, further improving multipath resistance and reliability.

• Methods for receiving correction information: How to obtain RTK correction data is also important. Besides installing your own base station and communicating via radio, you can receive corrections over the Internet from public or commercial RTK network services (VRS-based, etc.). Network RTK using the Ntrip protocol has become common, so check whether the receiver has an Ntrip client function and supports mobile communications. In areas without network coverage, such as tunnels or mountainous regions, direct communication via a radio modem can be useful.

• Positioning accuracy specs: Check the catalog-listed positioning accuracy (horizontal/vertical). A high-performance receiver may have, as a guideline, a fixed solution of approximately horizontal 8 mm (0.31 in) + 1 ppm and vertical 15 mm (0.59 in) + 1 ppm (RMS). For example, at a 10 km distance from the base station, the horizontal error would be calculated to be about 18 mm. Note that vertical accuracy is often about 1.5 times the horizontal accuracy. Also compare the time required for initial fix (usually several seconds to several tens of seconds) and recovery time when the rover loses and then regains fix.

• Communication interfaces: Confirm methods for communication between base and rover and for external connections. Many surveying RTK receivers have built-in UHF radio modems for direct base↔rover communication (in which case a radio license may be required in Japan). For network RTK, the rover needs mobile connectivity, so models with a SIM slot or built-in LTE modem can obtain corrections independently. Even if the receiver lacks mobile support, it is common to connect via Bluetooth to a tablet or controller and receive corrections via tethering. Bluetooth is included in most models, and some offer Wi‑Fi access point functionality for smartphone settings. Choose a model with communication methods that match your site operations (presence of radio modem, SIM support, Bluetooth version, etc.).

• Internal memory and data logging: It is important whether the receiver can record raw observation data (e.g., RINEX) as well as outputting coordinates during RTK. Many receivers save observation data to internal memory or external SD cards for static positioning or post-processing (PPK). Large-capacity memory is reassuring for long continuous observations; some products support direct export to USB drives or cloud synchronization. Check recording formats and memory capacity as needed.

• Environmental ruggedness: Since these devices are used in harsh outdoor environments, dust/water resistance and shock resistance are important. Many surveying devices have IP65–IP67 dust/water protection—IP67, for example, means “no ingress of dust and can withstand temporary immersion in water.” Major manufacturers’ products commonly have IP67 and shock resistance such that they survive drops from 2 m (6.6 ft) onto concrete. Check the operating temperature range to ensure specifications are not exceeded in extremely cold or hot environments; material and battery performance affect temperature tolerance. Choose a product with reliability to withstand long-term field use.

• Battery operating time: Check built-in battery life for full outdoor operation. RTK receivers perform high-precision computation and communication and can consume considerable power; continuous operation varies by model from about 5–10 hours to nearly 20 hours for energy-efficient designs. For example, Emlid’s Reach RS2 can perform continuous RTK positioning for over 18 hours on a single charge. For long surveying sessions, battery swaps may be necessary, so some models have dual hot-swap battery mechanisms. Conversely, ultra-compact smartphone-connected devices may only last a few hours, so plan for spare batteries or external power. Always confirm the catalog “continuous operation time” to ensure battery capacity matches your site work duration.

• Size and weight (portability): Device size and weight affect mobility on site. Conventional fixed GNSS receivers, which integrate antenna, battery, and radio, often weigh around 1 kg. Recently, mobile and wearable RTK receivers that pair with smartphones have appeared, with weights of a few hundred grams. For example, all-in-one receivers from major manufacturers like Trimble, Topcon, and Leica generally weigh about 1.0–1.5 kg, while smartphone-integrated devices such as our LRTK are palm-sized and highly portable, weighing around 125 g. There are reports that field surveys in mountains that formerly required two people could be completed by one person using LRTK; portability directly reduces labor. However, miniaturization tends to trade off antenna performance and battery capacity, so balance portability with necessary performance.

• Software integration and usability: Alongside hardware performance, the usability of bundled software and apps is important. Many major manufacturers provide a dedicated controller terminal and surveying software for end-to-end workflows from field observation to checking against design data. Emerging manufacturers often opt for control via generic smartphones or tablets. For example, Emlid receivers can be configured and managed via a smartphone app. LRTK provides a dedicated mobile app and cloud service to instantly share collected point clouds and photo-tagged positioning records. Data compatibility with surveying CAD or GIS (DXF, LandXML, Shapefile, etc.) directly affects field workflows. Before purchasing, confirm whether the RTK receiver will integrate smoothly with your existing or planned software, and check for available SDKs. Software usability affects field efficiency, so select while imagining actual operational workflows.

Based on the above points, choose an RTK receiver with performance and features that meet your company’s needs without excess. Both conventional fixed and smartphone-connected types have merits; decide which type best suits whether you will operate base stations or prioritize portability.

Applications to point cloud scanning and photogrammetry

One primary application of RTK receivers is obtaining point cloud data and applying them to photogrammetry. Point clouds acquired by laser scanners or drone photogrammetry can record sites as high-density 3D information, enabling wide-ranging use from design and construction to maintenance. High-precision 3D surveying traditionally required expensive LiDAR equipment and specialists, but nowadays point clouds can be obtained easily even with smartphone cameras or built-in LiDAR. For example, recent iPhones and iPads include LiDAR sensors that can generate 3D point clouds by simply scanning surrounding areas over a range of several meters (several ft).

Combining RTK receivers with this workflow makes it possible to attribute absolute coordinates (in a public coordinate system) to the acquired point clouds, which is revolutionary. Typically, point cloud models from photogrammetry are in arbitrary local coordinate systems even if they are high-precision; aligning them to map coordinates later required control points and scale adjustments. However, if you record the shooting position coordinates of each photo with an RTK receiver attached to the smartphone, or apply RTK coordinates sequentially during LiDAR scanning, the resulting point cloud is obtained already aligned to the surveying coordinate system. This eliminates the need to place ground control targets and greatly simplifies post-processing point cloud alignment. For example, in an inspection beneath a bridge, a worker scanned the lower bridge surface with an iPhone while a network RTK receiver attached to the smartphone provided centimeter-level coordinates to the point cloud—allowing a task that previously required specialized equipment and a large crew to be completed by one person. The era in which anyone can perform high-precision 3D surveying with just a smartphone is approaching.

Furthermore, point clouds with absolute accuracy provided by RTK can be immediately integrated with other spatial information. For example, overlaying design CAD data on the acquired point cloud on a tablet instantly visualizes discrepancies between as-built and design conditions, aiding plan revisions and safety checks. Because point clouds record the site as-is in 3D, once acquired they allow cutting arbitrary cross-sections or remeasuring dimensions later, so the data are highly reusable. By combining RTK receivers with drone photogrammetry or smartphone LiDAR scanning, you can achieve high-precision 3D point cloud acquisition with unprecedented speed and ease, strongly accelerating DX (digital transformation) in construction management.

Indoor positioning and AR utilization

RTK’s application range is not limited to outdoor surveying. Positioning and measurement needs also exist in indoor and underground spaces where GPS satellite signals do not reach. Pure RTK-GNSS cannot function where satellite signals are unavailable, but recently solutions that use smartphone AR (augmented reality) technology and IMUs (inertial measurement units) to perform relative indoor positioning have emerged. For example, by first obtaining RTK coordinates for a building entrance or other reference point outdoors and then using the smartphone’s AR functions to position indoors from that starting point, it is possible to perform positional measurements indoors where GPS cannot be used. This hybrid positioning is effective for measurements that cross indoor/outdoor boundaries, such as recording locations of pipes in ceilings or buried elements in walls.

RTK combined with AR is also attracting attention for construction support. With RTK providing high-precision coordinates, design drawings or BIM models can be overlaid in true-to-scale, accurately positioned on a smartphone or tablet screen. For example, if you want to install a pile at a point on the design drawing, pre-setting the coordinate allows a worker to be guided to that point via the smartphone AR display and mark the pile location within a few centimeters. This coordinate navigation function enables a single person to perform layout work that previously required a two-person transit and leveling team, greatly reducing labor. LRTK’s mobile app includes a “coordinate guidance” function that can guide workers to specified points with cm level accuracy (half-inch accuracy).

Using high-precision RTK and smartphone AR allows accurate single-person positioning guidance and layout. The photo shows an optional pole (monopod) with an LRTK receiver and smartphone mounted to measure pier positions. Using a pole makes it easy to adjust height offsets, and separating the smartphone from the receiver body for operation as needed enables efficient surveying and marking.

Whether indoor or outdoor, acquired high-precision data can be instantly shared and used via the cloud. For example, LRTK offers a photolog function that tags photos with location information and plots them on a cloud map, allowing the precise later identification of locations for photos taken during indoor inspections. In this way, RTK receivers serve as the infrastructure supporting real-time positioning + AR on site and contribute to improved efficiency in construction management and inspection tasks regardless of indoor/outdoor distinctions.

Benefits of introducing RTK

As described above, using RTK-capable receivers offers many benefits. The greatest advantage is dramatic labor reduction and speed improvement. Surveying and layout tasks that previously required multiple people can be performed by one person, reducing human resources. Introducing point cloud measurement can reduce the number of on-site measurements, eliminate redundant tasks, and lower costs through automation. For example, on one site, crack inspections using a tablet LiDAR allowed what previously took 1–3 days for photo compositing and drafting to be completed in about 5 minutes, reducing outsourced work by 30–40%. Such rapid digital measurement directly shortens schedules and improves productivity.

Moreover, combining RTK with point clouds and photogrammetry improves recordability and data usability. Because you can store three-dimensional information of existing conditions that were hard to capture with flat drawings or photos, the data become valuable assets for pre/post-construction comparison, quality inspection, and future maintenance planning. Reusing acquired data reduces the need for additional surveying and allows measuring only truly necessary spots, realizing further efficiency.

These effects make RTK receiver introduction a driver for on-site DX. By centering on high-precision position information and integrating point clouds and AR technologies, processes that were once fragmented—surveying, design, construction, and maintenance—become consistent through data. This reduces human error and accelerates decision-making, contributing to improved quality and safety. We are entering an era where a single receiver can cover “from point cloud scanning to indoor positioning,” and RTK receivers will increasingly become indispensable tools for site personnel.

Simple surveying with smartphone RTK "LRTK"

Finally, as a solution to easily realize the versatile RTK uses described above, we introduce LRTK. LRTK is a small RTK-GNSS receiver developed by Reflexia Inc., a startup from Tokyo Institute of Technology, and is a smartphone-integrated all-purpose surveying instrument that mounts on iPhone and iPad. The pocket-size housing, weighing about 125 g and 13 mm (0.51 in) thick, contains a high-precision GNSS antenna and battery and connects to smartphones via Bluetooth or Lightning. By attaching it to a smartphone you can achieve centimeter-level positioning, and it functions as an all-in-one surveying device for coordinate measurement, point cloud scanning, layout (staking), and AR-based on-site projection of design data. Acquired data are shared to the cloud on the spot, allowing office staff to instantly check field measurement results.

LRTK supports multi-GNSS (GPS/GLONASS/Galileo/Michibiki) and is compatible with Japan’s electronic reference point network RTK correction services and Michibiki’s CLAS augmentation signals. This enables stable centimeter accuracy across urban to mountainous environments, and a “network-outage-capable model” that receives augmentation signals directly from satellites allows high-precision positioning even when network coverage is unavailable. The field app “LRTK Phone” provides intuitive operation for single-point positioning, continuous positioning, photo measurement, coordinate navigation, AR surveying, and other rich features. It is designed so that anyone can obtain point clouds with absolute coordinates using one hand, and its ease of use means non-certified field staff can operate it.

In addition, LRTK is offered at very low cost compared to buying multiple dedicated devices. While no public price is listed, it is described as an “ultra-affordable price that allows one device per person,” making it feasible to equip all site workers without excessive budget strain. The convenience of keeping it in a pocket and using it whenever needed has led to many reports of “dramatically improved site productivity” and “remarkably streamlined surveying work.” If you are unsure which RTK receiver to choose, consider the smartphone RTK solution offered by LRTK. LRTK, which provides all-in-one site DX from positioning and measurement to cloud sharing, should be a recommended RTK receiver for your business.

FAQ

Q1. What is the difference between RTK positioning and ordinary GPS positioning? A. Standalone GPS (GNSS) positioning typically has errors on the order of several meters, whereas RTK positioning uses correction data from a base station to correct errors in real time, achieving centimeter-level accuracy. A major difference is that RTK uses two receivers—a reference station and a rover—and the reference station’s calculated error information is sent to the rover for correction.

Q2. Do I need a base station to use an RTK receiver? A. It is not always necessary to set up your own base station. While you can place your own base station (conventional RTK), network RTK that uses correction services from the Geospatial Information Authority of Japan’s electronic reference point network or commercial correction services is now mainstream. With network RTK, the rover is configured as an Ntrip client and receives correction data via mobile communications. Therefore, centimeter-level positioning is possible without a base station as long as there is Internet connectivity. However, in sites without network access, such as tunnels, you may still perform RTK positioning using your own base station and radio communication.

Q3. Can RTK positioning be used indoors? A. RTK-GNSS cannot be used directly indoors where satellite signals do not reach. However, high-precision GNSS can be used for indoor positioning with some ingenuity. One method is to obtain RTK coordinates at a building entrance before entering and then perform relative surveying indoors using the smartphone’s AR functions or a laser distance meter; this provides outdoor-referenced coordinates for indoor measurements. There are also attempts to achieve centimeter-level indoor positioning by combining ultra-wideband (UWB) beacons or proprietary tracking systems. LRTK offers features to respond to seamless indoor/outdoor positioning needs, such as smartphone AR integration and Michibiki signal augmentation for “measurements even outside GPS coverage.”

Q4. What are the benefits of using RTK for point cloud surveying? A. The biggest benefit is that you can attach accurate absolute coordinates to acquired point cloud data. When creating point clouds via drone photogrammetry or iPhone LiDAR, without RTK the resulting 3D model’s position will not match map coordinates. Traditionally, you needed to place control targets with known coordinates on site and align the point cloud model in post-processing. Using RTK eliminates that step and provides high-precision coordinates to each photo or point cloud at the time of capture. As a result, the data can immediately be overlaid on CAD drawings or GIS maps after processing, dramatically improving productivity. RTK also enables wide-area topography to be surveyed with fewer photos and reduces labor for placing control points.

Q5. What model is recommended for someone choosing an RTK receiver for the first time? A. The appropriate receiver depends on your use case, but broadly consider fixed-type and mobile-type options. If you plan base station operations and need high ruggedness and stability, fixed-type RTK receivers from major manufacturers such as Trimble, Topcon, and Leica offer reliability. If you prioritize portability and ease of use and want to survey directly from a smartphone or tablet, smartphone-coupled RTK receivers like Emlid’s Reach series or Reflexia’s LRTK are recommended. LRTK, in particular, is compact, lightweight, and well integrated with apps, making it user-friendly for beginners. The important thing is to select a model that meets your company’s requirements in terms of supported GNSS, accuracy, and communication methods, as outlined in this article. Consider budget and future expandability when making your choice, and find the optimal RTK receiver for your needs.