In construction and civil engineering sites, centimeter-level high-precision surveying is essential to ensure that the work is done according to the design plans. However, the accuracy of conventional GPS positioning is typically around 5 to 20 meters, which is a significant error margin. Traditionally, total stations or expensive GNSS surveying equipment were required. These traditional methods demanded skilled technicians and multiple workers, leading to challenges in the surveying industry, such as labor shortages and increased costs.

In recent years, RTK surveying using a smartphone combined with a portable GPS device has emerged as an innovative solution to address this challenge. By attaching a pocket-sized RTK-GNSS receiver to a smartphone, anyone can easily achieve centimeter-level high-precision positioning.

The smartphone transforms into an all-in-one surveying tool, and since surveying data can be shared in real-time on the cloud, it can be immediately utilized between the site and the office. Compared to traditional equipment, it is low-cost and easy to implement on a one-to-one basis, making it a technology that strongly supports the digital transformation (DX) of the construction industry.

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The Mechanism of RTK Positioning Using a Smartphone + Portable GPS Device

So, how is RTK positioning achieved using a smartphone and a portable GPS device? RTK (Real-Time Kinematic) is a positioning technology that utilizes error correction information sent from a reference station with a known position, allowing the receiver at the moving station to achieve high-precision positioning to the centimeter level in real-time. Specifically, both the reference station (such as public electronic reference points or base stations) and the target point (moving station) simultaneously receive GNSS satellite signals, and the positioning data from both stations are compared to correct the errors. By applying this correction information to the receiver via the smartphone, errors that would normally be several meters with standalone positioning are reduced to just a few centimeters.

In the case of smartphone + portable GPS devices, the smartphone connects to the local reference station network (such as GNSS reference point networks or private correction services) via the internet to obtain real-time correction data (such as RTCM messages). The portable device receives satellite signals through a high-performance multi-GNSS antenna (supporting not only GPS but also GLONASS and Michibiki, etc.), and the smartphone app calculates the precise coordinates. The latest devices are compatible with multiple frequency bands and support "CLAS" correction signals broadcasted by Japan’s quasi-zenith satellite Michibiki, allowing for centimeter-level positioning even in areas with no communication network. This makes stable, high-precision surveying possible even in environments where base station communication is difficult, such as in mountainous regions or disaster sites.

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Benefits of Introducing Portable GPS Devices

RTK surveying using a smartphone combined with a portable GPS device offers several advantages that traditional methods do not provide. The main benefits are summarized below:

• Instant Cloud Sharing: Surveying results and observation data can be saved to the cloud on-site, allowing for real-time information sharing with the office or other team members. For example, data can be immediately used for creating drawings or reports after surveying, which improves the speed of operations.

• Automatic Processing via Surveying App: The surveying app on the smartphone automates tedious processes such as coordinate conversion, diagramming, and point naming. Conversions to the rectangular coordinate system and distance calculations between points are completed within the app, eliminating the need for manual calculations or post-processing on a PC.

• Increased Efficiency and Reduced Workforce: Tasks that traditionally required two or more surveying specialists can now be completed by just one person using smartphone RTK. No setup of equipment is required, reducing preparation time, allowing more points to be measured in a shorter time. This reduces the need for personnel while also preventing task specialization, as the intuitive app interface can be used by individuals without specialized expertise.

• Cost Reduction: Portable RTK-GPS receivers are much more affordable than traditional surveying equipment, and since a smartphone is all that is needed, initial investment is significantly reduced. It is more economical than renting or maintaining expensive total stations or GNSS surveying devices, and it becomes easier to implement a "one device per person" system where every field staff member carries a device.

• Instant Data Utilization and Analysis: As data is digitally accumulated during surveying, it can be instantly used for terrain analysis or incorporated into as-built management, and accurate location information can be added to photos taken. This eliminates the need for paper field notes or data entry at a later time, contributing to the digitalization and efficiency of the entire workflow.

 

While traditional total stations boast millimeter-level accuracy, they are inefficient for large-scale surveys due to the time required for equipment setup and the need for line-of-sight during measurements. In contrast, with smartphone + RTK-GPS, measurements can be taken anywhere with a clear view of the sky, and complex setup is not required. Additionally, while specialized knowledge is required for dedicated equipment, smartphone app operations are intuitive, reducing training costs. These differences make smartphone RTK surveying one of the optimal solutions for driving construction DX.

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Introduction to LRTK Products

Among RTK surveying devices that utilize smartphones, the LRTK series from Refexia has garnered particular attention. LRTK is an ultra-compact RTK-GNSS receiver that attaches to an iPhone/iPad. Despite its pocket-sized dimensions (weighing 125g and 13mm thick), it is equipped with an internal battery and serves as a versatile surveying terminal capable of handling any surveying scenario. It is used by easily attaching it to a dedicated smartphone case, and if needed, it can be mounted on an optional monopod (pole) to measure height. The device supports multiple frequencies and offers high positioning stability. As mentioned earlier, it is also compatible with the Michibiki CLAS signal, allowing it to maintain accuracy even in areas with no communication network, which differentiates it from competing products.

The price is set at a very reasonable level, making it easy for anyone to adopt, depending on the site’s needs. In fact, the LRTK Phone is expected to "greatly improve productivity in field operations," with reports of it maintaining high precision even in environments where GPS reception is challenging, such as forests. It also features functions like automatically recording position coordinates and orientation in photos taken on-site, making it useful not only for surveying but also for infrastructure inspections and disaster surveys. As such, it has garnered attention from fields beyond construction and surveying.