How to Choose a GNSS Device Successfully: Latest Trends to Know Before Deployment

Recently, the demand for high-precision positioning has increased in situations such as surveying and construction sites, and more cases are considering the introduction of GNSS terminals (high-precision GPS surveying devices). Using GNSS terminals enables precise satellite-based positioning and can streamline conventional surveying tasks. However, there are various types of GNSS terminals, and if you do not choose an appropriate model, it can lead to failures such as "not achieving the expected accuracy" or "being unable to operate it effectively on site."

In this article, to help prevent such failures, we explain the basic functions and types of GNSS terminals, the key points to pay attention to when introducing them, selection points for each application, common on-site failure examples and how to avoid them, and the latest trends you should be aware of. Finally, we also introduce an example of implementing simple surveying using the latest smartphone-connected RTK GNSS terminal "LRTK" and its advantages. To avoid regretting your choice of GNSS terminal, please use this as a reference before adoption.

Basic Functions and Types of GNSS Terminals

A GNSS (Global Navigation Satellite System) terminal is a device that receives radio signals from multiple positioning satellites, including GPS, and calculates its own position (latitude, longitude, height). Receivers that support not only the United States' GPS but also Russia's GLONASS, Europe's Galileo, China's BeiDou (BeiDou), and Japan's Quasi-Zenith Satellite System (QZSS, commonly known as Michibiki) are common, and these systems are collectively referred to as GNSS. By simultaneously capturing signals from multiple satellites, a device can determine its current location anywhere on Earth, and typically if 4 or more satellites can be tracked, 3D positioning is possible.

The basic functions of GNSS terminals are receiving satellite signals and calculating position coordinates, but there are several types of positioning methods. Standalone positioning (single-point positioning) is performed with only one receiver, and typical accuracy is on the order of several meters (several ft) to about 10 m (32.8 ft). The GPS built into smartphones and car navigation systems also uses standalone positioning; although this accuracy is sufficient for everyday use, it is unsuitable for surveying or precise construction management of heavy machinery. What is used instead is relative positioning, and a typical example is RTK positioning (Real Time Kinematic). In RTK, you prepare one additional receiver called a base station, and by sending the error information between the base station’s known position and the mobile station (the rover) to the rover and performing real-time correction, you can achieve high-precision positioning with errors of several centimeters (several in). With RTK-GNSS–compatible terminals, under appropriate conditions you can obtain positioning accuracy of about 2–3 cm (0.8–1.2 in) horizontally and within 5 cm (2.0 in) vertically.

Another technology that has become more widespread in recent years is augmentation techniques such as network RTK. This is a method of achieving high-precision positioning by using correction information from a reference station network delivered via the Internet, or augmentation signals transmitted from satellites, without the user having to set up a reference station themselves. For example, in Japan there are commercial correction services that use the Geospatial Information Authority's network of permanent control stations (GNSS Continuous Observation System), and the Quasi-Zenith Satellite Michibiki provides a centimeter-level positioning augmentation service (CLAS) (half-inch accuracy). GNSS receivers that support these services can receive error correction information via a communications network or via satellite communications and perform real-time centimeter-level (half-inch accuracy) positioning with the receiver alone (rover only). Traditionally, accuracy declined as the distance from the reference station increased, but network RTK achieves stable accuracy over wide areas by generating virtual reference stations from data at multiple reference points. However, all of these methods assume an environment with good sky visibility for adequate reception of satellite signals, and care must be taken because GNSS may not function or may not provide accurate positioning in mountainous areas, urban canyons with high-rise buildings, tunnels, and the like.

Key Points to Consider When Deploying GNSS Terminals

When selecting a GNSS terminal, it is advisable to compare and evaluate products by focusing on the following points.

• Positioning accuracy: Check whether the device can meet the required accuracy level. If accuracy of a few centimeters (a few in) is required, RTK-capable devices or those supporting network corrections are essential, and the types of satellites available and the frequency bands (whether it supports multi-GNSS and multi-frequency) also affect accuracy and stability. Conversely, for simple positioning purposes where meter-level (m (ft)) accuracy is sufficient, an expensive high-precision device may not be necessary. Choose a device with accuracy specifications that match your company's intended use.

• Portability: Because these devices are carried and used on-site, size, weight, and shape are also important. Traditionally, stationary tripod-mounted units were the norm, but in recent years handheld types and small, lightweight units that attach to the end of a pole have appeared. If a unit is light and compact, it is easy to carry for high-elevation work, surveying in mountainous terrain, and deployment to disaster sites. Dust- and water-resistance, shock resistance, and battery runtime—features that allow outdoor use—can also be considered part of portability.

• Ease of operation: Whether the control system is intuitive enough to be used by non-specialist survey technicians is also a key point. Models that require a dedicated controller may take time to master, but devices that connect to smartphones or tablets and can be operated via an app are more likely to be accepted by on-site personnel because they can be used on familiar screens. The availability of Japanese-language display and support, and the thoroughness of the manual, also affect operability. If possible, we recommend trying the actual device on site to check menu clarity and button layout.

• Connection method: GNSS terminals not only obtain position information from satellites but also require some form of communication to receive correction data for higher accuracy and to output positioning results. Depending on the device, there are various types: those that connect to a controller via Bluetooth or USB, those with a built-in SIM card that can connect directly to the internet, and those that communicate with a base station via UHF radio. You need to choose a method that fits the communication environment at the site where it will be deployed. For example, if you will use it outside internet coverage areas, a local radio method is necessary, whereas in urban areas it is convenient to connect the terminal to a smartphone via Bluetooth and use the smartphone’s mobile data to link to network RTK.

• Cloud and app integration: Ease of managing and sharing positioning data is also important. Recent GNSS devices work with dedicated apps and cloud services, allowing acquired data to be uploaded to the cloud in real time and synchronized between the field and the office. Cloud integration lets you immediately check coordinates and photos of points measured in the field from the office, streamlining reporting tasks. Functions for exporting positioning data to CSV or map formats, and compatibility with other software (ease of importing into CAD and GIS), are also important checkpoints.

• AR and Point Cloud Support: While standalone GNSS devices primarily perform position measurement, products that can integrate with AR (augmented reality) technology and 3D scanning have recently begun to appear. For example, you can support stakeout work by correcting positions with GNSS while displaying blueprints or target points as AR overlays on a smartphone or tablet camera feed, or combine a smartphone’s built-in LiDAR scanner or an externally connected 3D laser scanner to acquire point cloud data with high-accuracy positional information. If you plan to digitize sites in the future, the extent to which a product supports these latest technologies should also be a consideration when selecting equipment.

Key Points for Selecting GNSS Terminals by Application

The performance and features that should be prioritized for a GNSS terminal vary depending on its intended application. Be sure to identify the selection points that match your company's use cases.

Civil surveying

In civil engineering works and surveying operations, there are many situations—such as determining boundaries and managing as-built conditions—where centimeter-level accuracy (half-inch accuracy) is required, so high-precision RTK-capable GNSS terminals are virtually indispensable. When performing long-distance control point surveys or wide-area site surveys, support for networked RTK corrections and stability to endure long-duration continuous positioning are also important. Because survey results are often handled in public coordinate systems (plane rectangular coordinate system or world geodetic system), pay attention to functions that can convert and output positioned coordinates to the Japan geodetic datum and compatibility with Geospatial Information Authority of Japan control points. Also, since field sites tend to be harsh environments with dust, high temperatures, and heavy rain, it is reassuring to confirm waterproof and dustproof performance and battery runtime.

Structural scanning

When performing 3D scans of structures such as bridges and buildings, a GNSS receiver plays an important role in assigning positional information to point cloud data. For example, when aligning point clouds acquired by laser scanners or drone surveys to map coordinates, control points measured with GNSS are required. In recent years, methods that combine smartphone LiDAR and GNSS to easily scan structures have also emerged; in such cases, a compact GNSS receiver that can interface with a smartphone is suitable. Because satellites can be difficult to receive in close proximity to structures, it is reassuring to use a receiver that supports multi-GNSS with a large number of tracked satellites and a data-logging function that enables post-processing accuracy correction.

Piling work (stakeout)

For applications that lay out building positions and mark pile-driving locations (stakeout) at construction sites, the usability of the GNSS device directly affects work efficiency. To accurately reproduce the coordinates from the design drawings on site, check whether the device or software is equipped with a surveying function (pile-driving guidance function) that shows in real time the difference between your position and the target position. If you combine a GNSS with an app that runs on a smartphone or tablet, the screen can provide intuitive guidance—arrows or AR displays like "Move ○ cm (○ in) north"—allowing one person to efficiently determine pile positions. Also, if the receiver has an tilt compensation function that can correct the position of the tip even when the pole is tilted, you can measure the pile head position even when you cannot stand the pole vertically due to obstacles, providing flexibility on site.

Disaster response

When surveying and assessing conditions at disaster sites, it is essential to obtain location information quickly and easily. Because communication infrastructure may be severed immediately after earthquakes or landslides, GNSS terminals that can perform positioning without a network connection are useful. For example, terminals that can receive Michibiki's CLAS signal can achieve centimeter-level positioning even outside cellular coverage, making them highly effective for emergency surveying in affected areas. Also, considering transport by helicopter or carrying on foot, equipment should be as lightweight and compact as possible. Since non-specialist personnel may carry out positioning tasks on site, products that allow simple operation—just power on and press a button—and that automatically save and share data can reduce the burden in the field.

Common on-site mistakes and how to avoid them

We summarize the troubles that are likely to occur on site after introducing GNSS terminals, along with preventive measures. To avoid repeating the same mistakes, take precautions in advance.

• Positioning impossible due to poor satellite reception: If the site is surrounded by forest or buildings, signals from satellites may not be received sufficiently, making positioning impossible or causing a significant drop in accuracy. To avoid this, measures such as performing positioning in a location with as much visibility as possible, using a longer pole to raise the receiver’s antenna above obstructions, or using a multi-GNSS receiver that can track a large number of satellites are effective. If you have time, choosing a time period with favorable satellite geometry (low GDOP) can also help. In locations where satellites cannot be acquired no matter what, consider other methods such as total stations instead of relying solely on GNSS.

• Positional accuracy is unstable: The coordinate values measured by GNSS can fluctuate over time, or in RTK there are cases where a fixed solution (FIX) is sometimes obtained and sometimes lost, causing uneven accuracy. Causes can include multipath errors from signal reflections, the distance from the base station and communication conditions, and equipment setup mistakes. As a countermeasure, you can reduce transient errors by conducting multiple observations at each survey point and taking the average. For RTK, making it a habit to record only after confirming that a fixed solution (FIX) is being obtained stably is also effective. Also, in environments with metal fences or vehicles nearby where reflection errors become large, accuracy can sometimes be improved by slightly shifting the positioning location or attaching a ground plane (reflected-wave removal plate) to the antenna.

• Data sharing is cumbersome: There are many cases where sharing surveying data collected on site with internal teams or clients is troublesome. For example, data recorded inside a device must be transferred to a PC and converted with proprietary software before it can be used, or mistakes occur because data were hand-copied into paper field notebooks. To prevent this, it is effective to use devices and apps equipped with cloud-integration features from the start and establish a system that allows you to upload to the cloud immediately after measuring on site and share with stakeholders. With a smartphone-connected GNSS receiver, positioning and cloud transmission can be automated simultaneously, greatly reducing the effort and errors involved in handing off data.

• Selecting a model that doesn't meet the purpose: Choosing the wrong device often leads to failures such as being unable to use it as intended or not achieving the expected results. For example, introducing a simple standalone GNSS into construction management that requires centimeter-level accuracy, or conversely buying an expensive, hard-to-handle surveying GNSS when only simple measurements are needed and ending up unable to make use of it. To avoid this, above all you should refer to the points mentioned above and clarify your needs and choose an appropriate model. If possible, it's reassuring to try a demo unit on-site before acquisition and verify that it can be used within your company's workflow without issues before purchasing.

Latest Trends in GNSS Terminals

Advances in technology mean GNSS terminals and positioning solutions are evolving every day. Stay on top of the latest trends and choose products with the future in mind.

• Proliferation of smartphone-connected GNSS: GNSS devices designed to be used in conjunction with smartphones and tablets are becoming more common. One advantage is that by using a handheld smartphone as the display and processing unit instead of a dedicated controller, system configurations can be simplified. They connect directly to smartphones via Bluetooth or Lightning, and dedicated apps can handle positioning, recording, and sharing, so even those with limited surveying experience can operate them intuitively. By integrating with the smartphone’s camera and AR functions they support on-site work, and by sending data to the cloud on the spot they enable information sharing with stakeholders, offering convenience that did not exist before.

• Low cost and high functionality: When one thinks of high-precision GNSS receivers, they used to seem very expensive and only affordable for specialized organizations, but in recent years costs have fallen dramatically due to the miniaturization and cheaper prices of electronic components and improvements in satellite signals. RTK-capable GNSS terminals are now available for under several hundred thousand yen, making them easier for small and medium-sized enterprises and local governments to adopt. At the same time, multifunctionality has advanced, with single units supporting multiple frequencies and multiple satellite constellations and incorporating tilt sensors and electronic compasses. Even inexpensive models increasingly match the basic performance of former high-end devices, expanding options in terms of cost-effectiveness.

• Realization of single-person surveying (reduced manpower): The advent of GNSS was itself a revolutionary change that made it possible for a single person to perform surveying work that had traditionally been carried out by two-person teams, and in recent years this trend has accelerated further. Carrying a lightweight GNSS rover and a tablet around the site allows one person to rapidly observe survey points on their own, significantly contributing to alleviating labor shortages and shortening work time. Products that incorporate features to enable efficient and reliable single-person measurements—such as visual guidance using AR technology and reduced measurement times through receiver tilt compensation—are becoming more common. The era in which each person carries one GNSS terminal is becoming a reality, helping to drive digital transformation at worksites.

Finally: Deployment Examples and Benefits of the Smartphone-Connected RTK GNSS Device "LRTK"

Finally, using the latest RTK GNSS terminal that can be used in conjunction with smartphones, LRTK, as an example, we will introduce its implementation effects and advantages. LRTK is a pocket-sized GNSS receiver that attaches to an iPhone and, when linked with a smartphone app, delivers centimeter-level positioning—a groundbreaking product. The compact unit, weighing only about 165 grams, is mounted on the back of the smartphone in a dedicated case and, by simply connecting via Bluetooth, your handheld smartphone instantly becomes a high-precision surveying instrument. Surveying work that previously required two people and a tripod can now be performed quickly by a single person anywhere with an LRTK and a smartphone.

The primary advantage of introducing LRTK is its ease of use and portability. The complete set of equipment is compact enough to fit in a chest pocket, so you can carry it while making rounds on site and quickly take it out to perform surveys when needed. It has a built-in battery that allows several hours of continuous positioning, and it can also be operated while charging with a mobile battery. By becoming a "one device per person" surveying tool that can be carried on site at all times, simple measurements that used to require waiting for the surveying team to arrive can now be carried out immediately by your own staff.

Next, another major appeal is that it combines high precision with multifunctionality. The LRTK is a multi-GNSS, multi-frequency receiver that supports RTK, consistently achieving accuracy of several centimeters (a few inches). Furthermore, because it can receive Japan’s CLAS augmentation signals, it can perform standalone centimeter-level (inch-level) positioning even in mountainous areas outside of communication coverage. In the app, point recording and averaging calculations can be done with a single tap, and conversions to the plane rectangular coordinate system and geoid height are also processed automatically. It has a variety of features to meet on-site needs, such as the Positioning Photo function that links photos and notes to measured points and saves them, and the Continuous Positioning (logging) function that records tracks at regular intervals. With this single unit you can handle everything from single-point surveying to stake-out for pile driving, as-built checks, and even overlaying expected completion drawings with AR, enabling all-in-one handling of on-site surveying tasks.

And the ease of cloud-enabled data sharing should not be overlooked. Data positioned with LRTK can be uploaded to a dedicated cloud on the spot and the results can be viewed immediately from an office PC. Because position information and point cloud data can be shared in real time within the team, there is no lag in reporting or review. For example, photos of damage taken at a disaster site are saved to the cloud with high-precision position coordinates and orientation information, so stakeholders can later verify the exact locations on a map. This removes the barriers between the field and the office and will dramatically accelerate the speed at which survey data can be utilized.

By introducing smartphone-linked RTK GNSS terminals, represented by LRTK, you can simultaneously resolve the long-standing bottlenecks of "equipment weight, manpower, and data organization." With the latest technology on your side, GNSS surveying should become more accessible and less prone to errors. Be sure to wisely choose the GNSS terminal that fits your company's needs and leverage it to improve on-site productivity and operational efficiency.