Easy, High-Precision Contour Surveying with a Smartphone! Instantly Grasp Site Topography

In recent years, driven by initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction promotion, the construction and civil engineering industries have accelerated ICT utilization and DX (digital transformation), bringing significant changes to surveying practices. Accurately understanding on-site topography is an indispensable process for everything from solar power system design to earthwork planning, progress management, and even disaster response. At the core of this is the “contour line” drawn on topographic maps, which intuitively indicates land relief and slope, enabling precise reading of site conditions. However, obtaining topographic survey maps with such contour lines has historically required considerable effort, time, and cost.

Now, thanks to the combination of smartphones and high-precision GNSS (RTK), an era is emerging in which anyone can easily survey topography with centimeter-level accuracy (half-inch accuracy) and instantly obtain detailed topographic data including contour lines. This article explains the importance of using contour lines to understand terrain and the practical benefits of a simple surveying method combining a smartphone, RTK, and 3D scanning, comparing it with traditional methods. We’ll confirm the advantages over conventional drone surveying, total station surveying, and outsourcing, and explore the potential of in-house surveying as a trump card for on-site DX. At the end of the article, we also introduce the workflow of the smartphone surveying solution “LRTK” to give you a practical image of on-site use.

The Importance of Understanding Terrain with Contour Lines

Contour lines are indispensable information that visually conveys elevation differences in the terrain and helps you understand site conditions. In practice, situations where contour lines are utilized include, for example, the following:

• Early-stage planning and design: In the initial consideration of a project, it is important to correctly understand the site’s topography. By using contour maps to comprehend slopes and relief, you can optimally place solar panels or buildings and plan layouts that account for elevation differences. Misreading the terrain can lead to later design changes or impractical construction plans, so verification with contour lines at an early stage is indispensable.

• Earthwork planning and earthwork volume calculation: When performing land development (cut and fill) in civil engineering, reading slope angles and elevation differences from contour lines allows you to plan where and how much to excavate or fill. Moreover, from contour data you can calculate cut-and-fill volumes and predict stormwater runoff paths to design drainage. With precise contour maps, you can prepare earthwork plans and quantities without excess or shortage.

• Construction progress management: During construction, regularly surveying the current terrain and updating contour lines lets you grasp discrepancies between the design model and the as-built condition in real time. For example, you can immediately confirm on-site whether embankment heights have reached design levels or whether there are irregularities in slope or flatness. Sequentially verifying as-built conditions prevents rework and improves quality control and progress-management accuracy.

• Disaster prevention and response: Topography understanding is also crucial for disaster response. Areas where surrounding contour lines are closely spaced indicate steep slopes and help identify landslide-prone locations. After heavy rain or earthquakes, quickly surveying how the terrain has changed and using the resulting contour line maps as materials for damage assessment and recovery planning is possible. Obtaining accurate topographic data immediately after a disaster can greatly shorten lead times from recovery planning to commencement of repair work.

Traditional Topographic Surveying Methods and Their Challenges

To obtain topographic maps with contour lines, the following surveying methods have traditionally been used. Each can secure a certain level of accuracy, but they have challenges in terms of manpower and cost.

• Surveying with total stations and similar instruments: The traditional method involves mounting a surveying instrument (TS) or level on a tripod while another staff member holds a rod to read points. Measuring a large site requires a team to take many points over several days, demanding significant labor and time. Also, because the acquired data are limited to elevation points at separated locations, terrain maps drawn from them risk missing fine relief details.

• Photogrammetry using drones: This method analyzes aerial photos taken by a camera mounted on a UAV to create 3D surface models and contour lines. It can automatically measure wide areas in a short time and has improved accuracy, but it requires a skilled operator and compliance with aviation laws. Post-flight image processing (photogrammetry) is needed, which requires a high-performance PC and several hours to days of processing time. Flights may be impossible depending on weather or site conditions, making scheduling and cost burdensome.

• Outsourcing to external surveyors: When a company lacks in-house surveying resources, it is common to outsource topographic surveys to surveying firms. While professionals can deliver high-quality contour maps, scheduling and contracting fees apply. If a single survey is insufficient and additional surveys are required, you must place new orders each time, making it difficult to respond immediately to urgent measurement needs.

While these traditional methods are proven, they have not fully met site demands in terms of speed and ease. What was needed was a new solution that could obtain high-precision topographic data in small crews and short timeframes.

High-Precision Contour Surveying with Smartphones and RTK

The key to solving the traditional challenges is a new surveying method combining a smartphone with RTK positioning. Modern smartphones are equipped with LiDAR scanners and high-performance cameras, which can be used to convert the surrounding terrain into 3D data (point cloud scans) simply by walking around the site. In practice, with iPhone-based 3D scanning, you can record ground and structures three-dimensionally by moving the phone while holding it up. However, a smartphone’s standalone GPS accuracy is only on the order of several meters, so point clouds obtained without correction lack sufficient absolute position accuracy. Sensor errors within the phone can also cause scan data distortion, leaving challenges to meet civil surveying accuracy requirements.

This is where RTK (real-time kinematic) high-precision GNSS positioning comes in. RTK uses a fixed GNSS receiver as a base station and a rover receiver that receive satellite signals simultaneously, and by performing real-time differential corrections for their error factors, RTK reduces positioning errors to within a few centimeters. Although this technology has long been used in civil surveying, conventional dedicated equipment was large, expensive, and required operational expertise. Recently, network RTK using mobile communications and augmentation signals such as Japan’s Quasi-Zenith Satellite System “Michibiki” CLAS have spread, making centimeter-class positioning (half-inch-class positioning) possible without a dedicated base station.

Combining smartphone 3D scanning with RTK positioning enables 3D surveying with centimeter accuracy (half-inch accuracy) using only a smartphone. In fact, smartphone surveying systems that incorporate high-precision GNSS have demonstrated horizontal accuracy of about ±1–2 cm (±0.4–0.8 in) and vertical accuracy of about ±2–3 cm (±0.8–1.2 in), meeting typical on-site surveying requirements. By assigning RTK-derived precise coordinates (latitude, longitude, height) to each point in the point cloud obtained by the smartphone’s LiDAR, the entire acquired 3D dataset is, from the start, a high-precision dataset on a public coordinate system. Because long-duration scans do not produce positional drift-induced distortion, the survey data can be overlaid precisely with design CAD data and survey drawings. In short, by integrating a smartphone with RTK, creation of topographic maps with contour lines—which previously required postprocessing and complex control point alignment—can now be performed accurately on-site.

One concrete solution that enables this smartphone × RTK surveying is LRTK. LRTK consists of an ultra-compact RTK-GNSS receiver that attaches to a smartphone and a dedicated app, designed to be easy for anyone to use. The next section examines the workflow of contour surveying using LRTK.

Workflow of Simple Surveying Using LRTK

Let’s go through the sequence of surveying site topography and obtaining contour lines using the smartphone surveying system “LRTK.”

• Field measurement (on-site surveying): Upon arrival at the survey location, attach the LRTK device to the smartphone and power it on. Start GNSS reception in the dedicated app, and in a few tens of seconds RTK high-precision positioning will reach a fixed solution (“Fix”). Once ready, begin surveying. Simply move the smartphone to the points you want to measure and tap a button in the app to record the latitude, longitude, and elevation of that point. No assistant or complicated operation is needed; one person can sequentially acquire survey points.

• Point cloud generation (3D scanning): To capture wide-area terrain, just walk around the site holding the smartphone and automatic point cloud scanning will occur. The phone’s camera and LiDAR capture the surrounding terrain as numerous points (a point cloud), and a 3D model is displayed on the screen in real time. Because LRTK’s high-precision positioning continuously corrects the entire point cloud to the correct location, long scans do not produce distortion, and you obtain an accurate copy of the terrain down to fine details. You can confirm the 3D point cloud reflecting surface undulations on site, ensuring nothing is overlooked.

• Contour line extraction: From the acquired high-precision point cloud data, contour lines can be drawn at arbitrary intervals. You can preview contour maps on the smartphone immediately after surveying, or import point cloud data into dedicated cloud services or CAD software to automatically generate contour lines at specified intervals. Extracting contour lines from high-density point clouds yields topographic maps that accurately represent even fine terrain features.

• Cloud sharing and analysis: After surveying, recorded data (point clouds, survey point coordinates, photos, etc.) can be uploaded to the cloud with one tap. In the cloud, data can be viewed and shared instantly from a PC browser; even without dedicated software you can rotate point clouds and measure distances and areas. By the time you return to the office, results can already be shared with stakeholders, so if there were missed measurements you can immediately instruct additional surveys and avoid rework. Connecting the field and office with digital data dramatically speeds up decision-making.

• On-site display with AR: High-precision data obtained with LRTK can also be overlaid on the real world using a smartphone or tablet AR feature. For example, projecting the contour lines or point cloud model you just measured onto the site camera view lets you intuitively grasp the terrain in situ. You can also AR-display design-stage 3D models (planned lines or completion models) to compare with current terrain. Gradients and positional discrepancies that were difficult to discern from drawings become obvious through AR, aiding immediate on-site verification.

As described above, using LRTK makes the entire process from survey acquisition to data utilization remarkably simple. What once required several people for topographic surveying can now be completed with a single smartphone, obtaining accurate contour line maps the same day and sharing them with stakeholders—bringing a major transformation to site workflows.

Comparison with Traditional Methods: Advantages of Smartphone Surveying

What specifically changes when surveying is done with a smartphone + RTK (for example, by implementing LRTK) compared to traditional surveying? The main points are summarized below.

• Required personnel: Traditional TS surveying typically required at least 2–3 people working together, but smartphone surveying can generally be completed by one person. Even without experienced surveyors, in-house staff can perform surveys, avoiding disruptions in sites with labor shortages.

• Equipment and setup: Traditionally, bulky equipment such as total stations, large GNSS receivers, tripods, and radios had to be transported by vehicle and set up. With LRTK, all you need is a smartphone and a palm-sized device. Heavy machinery and equipment vehicles are unnecessary, and surveying can start immediately upon arrival at the site.

• Survey area and accuracy: Previously, due to time and personnel constraints, survey points were often thinned out, but handheld point cloud scanning enables wide-area, high-density measurement in a short time. Because the entire 3D dataset is positioned with centimeter accuracy, local errors do not accumulate, allowing accurate recording of terrain throughout large sites. Drone imaging may fail to capture ground surface when covered by vegetation, but handheld scanning allows you to part undergrowth and directly measure the ground surface when necessary.

• Data processing: Historically, converting field notebooks to drawings or processing drone photos in dedicated software required substantial postprocessing. Smartphone surveying automatically records and saves data during measurement, and cloud integration enables instant sharing and analysis. You can use the measured topographic data the same day, greatly reducing time for report preparation and drawing production.

• Cost and insourcing: High-precision surveying instruments are costly to purchase and maintain, and repeated outsourcing becomes a financial burden. In contrast, LRTK devices can be introduced at a price range that is a fraction of traditional equipment, dramatically reducing operating costs. More companies are insourcing surveys to cut external contracting costs and accumulate data and know-how internally.

As shown above, smartphone surveying simultaneously reduces personnel, time, and cost while improving data accuracy and convenience. It is truly a technology that can transform on-site surveying practices.

Conclusion

Contour surveying using smartphones and RTK is an innovative effort that strongly promotes on-site DX. Insourcing and accelerating surveying work dramatically improve productivity, and effective use of the resulting digital data enhances construction quality. This cutting-edge technology, aligned with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative, is likely to become the new standard in future construction and civil engineering sites.

Topographic surveys with contour lines, which used to rely on experienced personnel, can now be performed accurately and easily by anyone using solutions like LRTK. The benefit of instantly “visualizing” terrain with a single smartphone is immeasurable. If you have not implemented it yet, consider introducing LRTK surveying to your sites. By leveraging the latest technology for contour surveying, you can dramatically streamline the terrain-understanding process and take a further step forward in DX for on-site operations.