Easy with a Smartphone! 3-Step Guide to Creating RTK Cross-Sections

Table of Contents

• Introduction

• Traditional Cross-Section Creation Methods and Challenges

• Step 1: Preparation (Smartphone and RTK Survey Setup)

• Step 2: High-Precision Data Measurement On Site

• Step 3: Point Cloud Processing and Automatic Cross-Section Creation

• Benefits of Creating Cross-Sections with Smartphone × RTK Surveying

• Recommendation: Simple Surveying with LRTK

• FAQ

Introduction

Cross-sections, frequently used in construction sites and civil surveying, can feel difficult for beginners to create. A cross-section is a drawing that shows the internal shape of terrain or structures when cut vertically along a reference line. In road works, they are used to check ground undulations, and for river levees they help evaluate structural strength from the cross-sectional shape; they are indispensable documents in many situations. In recent years, digitization of surveying (ICT utilization) has progressed, and there is increasing demand to further streamline traditional cross-section creation methods. However, even when instructed to “create an accurate cross-section,” inexperienced engineers may struggle to know where to start.

Creating cross-sections requires careful surveying on site. Height data must be obtained at many points, plotted on a drawing, and connected with lines; with traditional methods this required skilled technicians and significant effort. The handling of surveying instruments, calculations, and drawing processes is complex, making it a high barrier for newcomers. As a result, beginners often feel anxious thinking “it seems difficult” or “I might make mistakes.”

This article explains in three steps how even beginners can surprisingly easily create cross-sections by utilizing a smartphone and RTK surveying. Using the latest technology, we introduce points that allow anyone to draw high-precision cross-sections in a short time, and at the end of the article we also introduce a convenient surveying solution called LRTK.

Traditional Cross-Section Creation Methods and Challenges

First, let’s look at how cross-sections were traditionally created. Typically, work proceeded as follows.

• On-site surveying with multiple people: A surveyor and an assistant go to the site and set up surveying instruments such as a level or total station. Usually one person operates the instrument while another stands at each point along the cross-section line holding a staff, so two or more people are generally required. Heights are read at each chosen survey point along the cross-section line and the values recorded. If the target section is long or the terrain complex, the number of survey points increases and measurements take more time.

• Organizing measurement data and calculations: The height and distance data recorded on site are brought back to the office and organized. Distances and elevation differences between survey points are calculated, and numerical tables for plotting the cross-section are prepared. Transcribing from field notebooks risks errors, and beginners especially need to be careful when handling numbers.

• Drawing the cross-section (tracing): Based on the organized data, the cross-section is drawn by hand on paper or by drawing lines in CAD software. The idea is to plot each survey point on a graph with distance on the horizontal axis and elevation on the vertical axis, then connect the points with lines. Inexperienced surveyors may misunderstand scales or make drawing mistakes, and a single cross-section can take a long time to complete. For long sections, this work must be repeated many times, making it very labor-intensive.

As described, traditional cross-section creation was a large-scale task requiring manpower and time. Because only a limited number of points could be collected, resolution was limited and subtle undulations between points could be missed. Complex instrument operation and tedious calculation and drawing procedures were high hurdles for beginners, creating the impression that “making accurate cross-sections efficiently is difficult.”

Step 1: Preparation (Smartphone and RTK Survey Setup)

The first step is preparation for surveying. Traditionally, it was necessary to set up complex instruments like total stations, but with a smartphone and RTK the preparation is much simpler. First, install a dedicated surveying app on the smartphone and prepare a compact high-precision GNSS receiver (antenna). Connect this receiver to the smartphone via Bluetooth and configure the app to enable RTK positioning. Specifically, connect the smartphone to correction data from national or private reference stations (GNSS correction information) via the Internet so that centimeter-level positioning (half-inch accuracy) can be performed in real time.

During the preparation stage, it is also important to confirm the location of the line where you want to take the cross-section. If a transverse line is specified on the design drawing, identify its start and end points on site. By using the smartphone’s map function and GPS you can grasp the approximate position. Traditionally it was also time-consuming to set survey point locations on site, but with smartphone surveying you can proceed while confirming positions on the map, allowing for efficient work. Once the equipment is ready and positions are confirmed, you are set to start surveying.

Step 2: High-Precision Data Measurement On Site

Next, move on to on-site measurement. Once the smartphone and RTK receiver are ready, begin collecting data along the cross-section line. Launch the surveying app and start the cross-section measurement mode (or point cloud scan mode). Hold the smartphone in one hand and walk slowly along the cross-section line while scanning the terrain.

At this time the smartphone camera or built-in LiDAR sensor captures the surrounding terrain, and the app automatically acquires high-density 3D point cloud data. At the same time, RTK provides high-precision positioning of the smartphone, so each recorded point in the point cloud is assigned accurate coordinates (latitude, longitude, elevation). In short, by simply walking and holding up the smartphone you can measure the coordinates of a large number of points that make up the terrain along the cross-section line.

For example, when measuring a slope cross-section, where traditionally representative points might be measured every few meters, smartphone measurement records a continuous collection of points that include fine undulations. Just like shooting a video, pointing the camera and moving allows anyone to obtain detailed on-site data in a short time. In addition, because the app screen lets you check acquisition status in real time, you can verify on the spot whether anything was missed or whether abnormal values are included. By measuring any missing sections as needed, you can avoid having to redo work later due to insufficient data.

Step 3: Point Cloud Processing and Automatic Cross-Section Creation

Finally, process the data and generate the cross-section. Upload the point cloud data obtained on site from the smartphone to the cloud for use (if you are outside an internet area, you can upload after returning to the office). When you send the data to the cloud, you can view the site point cloud in a dedicated 3D viewer that runs in a browser.

If you specify the position where you want to create a cross-section in the viewer, a cross-section along that line is generated instantly. The software analyzes the elevation information of the portion of the massive point cloud that intersects the specified line and draws the cross-sectional shape. In the past you would have had to connect each survey point one by one to draw a cross-section; now you can obtain it with the push of a button.

Moreover, if you have an acquired point cloud, you can cut cross-sections at any location. Even if you decide on site, “I want a cross-section here too,” there is no need to remeasure. The flexibility to simply specify a line on the point cloud and generate a cross-section at any location is a major advantage. For example, even if you need transverse cross-sections at 10 m (32.8 ft) intervals for road work, you can create multiple cross-sections from the point cloud obtained in a single field scan. This flexibility means you don’t have to fix the exact survey line position in advance and can obtain the necessary drawings later as required.

Generated cross-sections can be checked on the screen immediately and can also be exported as CAD data in DXF format. Exporting to DXF allows you to overlay the cross-sections on existing design CAD drawings or submit them as electronic deliverables. The previously time-consuming drawing work is greatly streamlined by using automatically generated data.

Benefits of Creating Cross-Sections with Smartphone × RTK Surveying

The new method of creating cross-sections using a smartphone and RTK surveying has the following advantages compared to traditional methods.

• Measurable by one person in a short time: On-site work can basically be completed by one operator. There is no need to carry heavy tripods or surveying machines; carrying just a smartphone and a compact receiver and walking is sufficient, so the entire task including setup and teardown is fast. As a result, cost reductions from reduced personnel and days are expected.

• Easy operation and quick to learn: You operate by following the smartphone app’s guidance, so it can be used without prior experience with specialized equipment. Difficult settings and calculations are automated, so even new engineers can become effective quickly.

• High-precision data with no omissions: Point cloud scanning allows nearly continuous measurement of terrain along the cross-section line, so fine undulations are captured in the data. There is no risk of forgetting to measure required locations, preventing situations where “important parts have no data.”

• Real-time confirmation of results on site: You can check progress and provisional cross-sectional shapes on the smartphone screen during measurement, so errors or omissions can be detected immediately. Additional measurements or corrections can be made on site, reducing the need for revisits or rework.

• Immediate use of digital data: Acquired data can be shared with the office via the cloud, and cross-sections automatically drawn from the point cloud can be used directly as CAD data. The flow from surveying to drawing is seamless, achieving great efficiency and paperless operations.

Recommendation: Simple Surveying with LRTK

Finally, as a concrete solution to realize cross-section creation using smartphone × RTK, we introduce LRTK. LRTK is an innovative smart surveying system composed of a smartphone, a compact positioning device, and cloud services. It is designed to be easy for beginners to handle and can execute the three-step workflow described above seamlessly on a single platform. The required equipment is minimal—just a smartphone and a compact receiver—which fits into a pouch or small bag, providing excellent mobility. On site, anyone can obtain high-precision point clouds even while operating the smartphone with one hand.

For example, with a smartphone that has the dedicated app installed and an LRTK receiver, anyone can easily acquire high-precision point cloud data on site. Acquired data can be uploaded to the LRTK cloud with a single button, allowing immediate 3D point cloud display and automatic cross-section generation on the spot. There is no need to install dedicated software or prepare a high-performance PC. LRTK handles the complicated surveying instruments and software operations in the background, so users can focus on intuitive operation and obtain high-quality results. Furthermore, acquired point cloud data can be used for analyses other than cross-sections, such as measuring distances, areas, and volumes.

By utilizing LRTK, not only cross-section creation but the entire process from on-site surveying to drawing is significantly streamlined. You can easily obtain precise current-condition data by one person and share information between the field and the office in real time. Surveying tasks that previously had to be left to experienced personnel can now be confidently attempted by newcomers thanks to LRTK. If you are thinking of starting “high-precision surveying easily with a smartphone,” please consider using LRTK. The official LRTK website also publishes case studies and detailed information, so if you are interested please check it out.

FAQ

Q: What is RTK? How is it different from ordinary GPS?

A: RTK stands for “Real-Time Kinematic” and is a high-precision positioning technology that uses GNSS (satellite positioning). Ordinary GPS positioning has errors on the order of meters, but RTK uses correction information from a base station to reduce errors to the order of a few centimeters. RTK positioning operates two receivers simultaneously—a reference station (fixed) and a rover (the surveyor’s unit)—and corrects the relative error with respect to the reference station to achieve high precision. In smartphone RTK, correction data from base stations such as those provided by the Geospatial Information Authority of Japan are used via the Internet. For this reason, RTK is widely used in civil surveying and construction where accurate measurements of position and elevation are required.

Q: What is needed to perform RTK surveying with a smartphone?

A: Basically you need a high-precision GNSS receiver and a smartphone surveying app that connects to it. A smartphone’s internal GPS cannot achieve high precision, so you connect an external GNSS antenna that supports centimeter-level accuracy (half-inch accuracy) to the smartphone via Bluetooth or cable. RTK also requires receiving correction information in real time, so you must connect to a service that distributes correction data (a GNSS reference station network) via the Internet. As a complete hardware and software solution, products like LRTK that bundle a smartphone app and receiver make adoption smooth.

Q: Can beginners with little surveying experience use it effectively?

A: Yes, smartphone-based RTK surveying systems are designed to be user-friendly for beginners. Unlike traditional surveying instruments, operation proceeds with intuitive smartphone controls and difficult settings and calculations are automated. If you are unsure, the app’s guidance messages and real-time measurement results let you proceed while checking, so there is no need to worry. After a few trials you will get the hang of it, and you can apply it to practical work without special qualifications or advanced knowledge.

Q: Is the accuracy of cross-sections obtained by smartphone RTK surveying sufficient?

A: With proper measurement, smartphone surveying using RTK can produce highly accurate cross-sections. Under good measurement conditions, horizontal positions are typically within about ±1-2 cm (±0.4-0.8 in), and elevation is within about ±2-3 cm (±0.8-1.2 in). RTK-GNSS itself is highly accurate, and point cloud scanning captures terrain in detail so fine undulations can be reproduced on cross-sections. RTK positioning has actually been increasingly used for as-built management, and it has been confirmed that required accuracy can be met. However, in locations where satellite signal reception is extremely poor, accuracy may degrade, so in such cases consider supplementary checks with a total station or other measures.

Q: Can you create cross-sections with a smartphone that does not have a LiDAR sensor?

A: Yes, even smartphones without LiDAR can acquire point cloud data using photogrammetry based on camera images. However, photogrammetry requires adequate surface texture and sufficient lighting, so acquisition accuracy can be affected by the environment. LiDAR-equipped devices can measure more stably in low-light or texture-poor conditions, but outdoors during the day a camera alone can generate a high-precision model without issue. Processing takes longer than with LiDAR-equipped devices, but the latest smartphone apps record continuous photos similar to shooting a video and can generate high-precision point cloud models. Therefore, even if you don’t have a LiDAR-capable device, you can still try creating cross-sections with an ordinary smartphone.

Q: Can it be used with any smartphone?

A: Currently the LRTK app is provided for iOS. It can be used on devices that can connect via Bluetooth to a compatible GNSS receiver. An Android version is planned, and the range of supported devices is expected to expand.

Q: Can smartphone RTK surveying be done in mountainous areas without network coverage?

A: In areas without Internet connectivity, obtaining correction information in real time is difficult, so some ingenuity is required. One method is to set up your own GNSS receiver as a base station on site and transmit correction data to the smartphone via radio communication so you can perform RTK without internet. Another method is to record positioning data on site and apply correction information later using a post-processing technique called PPK (Post-Processed Kinematic), which allows you to achieve high accuracy through post-processing even if you cannot get real-time accuracy on site. However, these procedures are more complex, so for beginners we recommend using locations with available network connectivity if possible.