RTK Data to CAD Software: A Simple Integration Workflow for Contractors

Table of Contents

• Basics of RTK Surveying

• The Significance of Applying RTK in CAD Software

• Traditional Surveying Workflow and Challenges

• The Emergence and Advantages of Smartphone RTK

• Procedure for Importing RTK Data into CAD Software

• On-site DX through Cloud Integration

• The Future of Simplified Surveying Realized by LRTK

• FAQ

Basics of RTK Surveying

RTK stands for "Real-Time Kinematic" and is a surveying method that corrects errors in satellite positioning systems (GNSS) in real time to achieve centimeter-level accuracy. With ordinary GPS positioning, errors of about 5–10 m (16.4–32.8 ft) occur due to the atmosphere and satellite clock offsets, but RTK surveying uses two receivers: a base station (a receiver installed at a known, accurate coordinate) and a rover (a receiver installed at the point to be measured). By the base station continuously sending error-correction data to the rover, the rover can compute its position with errors within a few centimeters. The base station and rover communicate in real time via dedicated radio or the Internet, allowing high-precision position information that cannot be obtained by standalone positioning to be acquired instantly.

This centimeter-level positioning (cm level accuracy (half-inch accuracy)) is also extremely important on civil engineering construction sites. For example, in tasks where slight positional deviations directly affect quality and safety—such as boundary surveying, as-built verification to confirm that construction matches the design, and machine guidance—the high accuracy of RTK is indispensable. Surveyors and technicians have traditionally utilized RTK-GNSS, but operating it has required specialized knowledge and expensive equipment.

This integration provides the following benefits to contractors. For example, by creating a current 3D ground model from surveyed terrain data and comparing it with the planned design alignment and base surface, they can instantly grasp the progress and any excesses or shortages of fills and cuts. Also, by comparing the actual as-built points of structures with the design model, they can verify construction accuracy on site and early identify locations that require correction. Instead of checking numbers on paper drawings, being able to visually confirm them on a digital 3D model helps reduce mistakes and accelerate consensus building.

Moreover, because data imported into CAD software can be used directly for drafting and quantity calculations, information collected on site can be reflected in deliverables without any loss. Previously, survey results had to be transcribed into CAD drawings by hand, but data integration greatly simplifies that work and accelerates DX (digital transformation) in construction management.

Conventional Surveying Workflow and Challenges

Traditionally, there were several hurdles to using RTK surveying on site. First is the high cost of equipment. Equipping a complete set of conventional RTK-GNSS receivers and dedicated controllers can require an investment on the order of several million yen, making it difficult for small and medium-sized contractors to adopt them casually. The equipment is also large-scale and heavy—for example, base stations mounted on tripods and mobile stations with antennas on long poles—so transporting and setting up the gear was cumbersome. At sites such as mountainous areas where radio signals are difficult to receive, it was necessary to secure line of sight between base and mobile stations to perform wireless communication, and in some cases radio-use license applications were required, adding operational complexity.

Secondly, there is the problem of specialized knowledge and personnel. To perform RTK surveying accurately, it is necessary to understand a series of procedures, such as setting the base station at a known point and configuring communications with the rover. Dealing with troubles that occur on site also requires advanced knowledge, and as a result it tended to become a situation where only a limited number of surveying specialists could handle it. Therefore, in routine construction management, although RTK is highly accurate, it has been difficult to use it every time, and on smaller sites many cases were handled by simple surveys using a tape measure or a handheld GPS. However, these simplified surveys have large errors and carry the risk of causing discrepancies with the design drawings and requiring rework later.

Third, the burden of data processing cannot be overlooked. Traditionally, data recorded in surveying instruments had to be transferred to a PC, organized with dedicated software or spreadsheet programs, and then reflected in CAD. Even when adding location information to photos, tasks such as manually linking captured images to survey points were required, so coordinating field and design data took time and effort. Sharing field measurement results in real time was also difficult, and many analog tasks were carried out on site—workers would write numbers in paper field notebooks and later use those notes to revise drawings.

Because of these challenges, RTK surveying, while attractive in terms of accuracy, has not become a tool that all field technicians can use daily for reasons such as "the equipment is expensive and heavy," "only skilled operators can use it," and "it takes time to make use of the data."

The emergence of smartphone RTK and its advantages

In recent years, smartphone RTK has begun to appear, transforming these circumstances. Smartphone RTK is a new method that combines a smartphone with a compact, high-precision GNSS receiver to realize RTK positioning in the palm of your hand. For example, by using a GNSS module weighing a few hundred grams that can be attached to a smartphone and performing positioning on a smartphone app while receiving correction information, you can achieve centimeter accuracy (cm level accuracy (half-inch accuracy)) comparable to conventional fixed equipment. Communications with reference stations often use the Ntrip method over the smartphone’s mobile network (the Internet), and a key feature is the convenience of not requiring specialized radio equipment or licenses. Furthermore, receivers that support the Quasi-Zenith Satellite "Michibiki" centimeter-level augmentation service (CLAS) have appeared in Japan, enabling high-precision positioning even in mountainous areas outside network coverage by receiving augmentation signals from satellites. As a result, an environment is being put in place where centimeter-level surveying (cm level accuracy (half-inch accuracy)) can be performed anywhere nationwide, by a single person without installing heavy base stations.

The advantages of smartphone RTK extend to cost and ease of use. High-precision positioning that used to cost several million yen with dedicated equipment can be introduced at dramatically lower cost with smartphone RTK. The equipment is compact enough to fit in a pocket, supports Bluetooth and Wi‑Fi connections, and requires no complicated wiring. Some battery-powered models allow continuous measurement for several hours or more, making them robust enough for surveying while moving around a site. Operation is intuitive via a smartphone app, so even construction managers without special training can complete surveying themselves on the spot. RTK-specific altitude measurements are also easy with smartphone RTK, so processes that used to be left to specialists—such as checking excavation depths and embankment heights—can now be confirmed immediately by the team.

By combining a smartphone camera and LiDAR sensor, you can perform geotagged photo capture and point cloud measurement for 3D scanning with a single device. Photos taken during positioning can be tagged with high-precision coordinates and orientation information, making it possible to later place those photos accurately onto CAD drawings. With a LiDAR-equipped smartphone, simply walking while scanning the surroundings can acquire high-density point cloud data, and by assigning RTK coordinates to that data you can generate 3D models that instantly align with map coordinates. In this way, smartphone RTK is revolutionizing field surveying work with the concept of a "one universal surveying instrument per person."

Procedure for Importing RTK Data into CAD Software

Now, let's look at the steps to actually transfer surveying data obtained with smartphone RTK and similar devices into CAD software. Below, we've organized a simple, step-by-step workflow that construction site personnel can easily follow.

• High-precision data acquisition on site: First, use smartphone RTK to survey the points or areas you want to measure on site. Before starting positioning, it is important to use the same reference coordinate system as the design drawings. If the project adopts Japan’s public coordinate system (Plane Rectangular Coordinate System), select the same coordinate system in the smartphone app or localize (calibrate) using known control points. Once prepared, sequentially observe the coordinates of the target points. For point-by-point surveys, assign names or codes to each survey point (for example, "Boundary Stone 1", "Shoulder A") and record them to make later organization easier. For area surveys, move across the target area to acquire multiple points or obtain point clouds using LiDAR scan mode.

• Saving and exporting positioning data: After the survey is complete, export the acquired data from your smartphone. In many cases, survey point data can be output in CSV or text format and include items such as point ID, coordinates (X, Y), elevation (Z), and comments. For point cloud data, save it as a LAS or PLY file or download it via the cloud. At this stage, reconfirm that the data’s coordinate system matches the one used in the design drawings. Even if you recorded positions as latitude and longitude, you can later convert them to a plane rectangular coordinate system in CAD software, but it’s smoother to standardize the system on-site beforehand.

• CAD software settings: Next, launch the CAD software and prepare to import the data. If you are creating a new drawing, set the drawing units and coordinate system in advance (e.g., meters and the planar coordinate system to be used). If you are adding to existing design data, open that drawing file. If the coordinate system you set matches the survey data, it will be placed in the correct positional relationship automatically during the import described below. Also, when handling large datasets such as point clouds, file sizes can become large, so it is advisable to prepare a lightweight working copy as needed.

• Importing Survey Data: Once you are ready, load the positioning data into your CAD software. For point data, use the [Insert] tab's [Import Point File] function and select the CSV or other file you exported earlier. In the format settings screen (column order and delimiters), if you map the fields correctly the numerous registered points will be plotted on the drawing at once. Field names and elevations are imported as attributes for each point, making it easy to create tables or display labels later. For point cloud data, use the CAD software's Point Cloud Attach function to load LAS data, etc. If necessary, preprocess the point cloud files and convert them to RCP format before attaching to improve performance.

• Data Utilization and Verification: Once the import is complete, the site survey data is reproduced in the CAD software. From there, that data is used to perform various analyses and verifications. For example, you can generate a ground surface TIN surface (triangular mesh terrain model) from the imported coordinate point cloud and compare it with the planned design surface to calculate the required fill and cut volumes. In as-built management, you can overlay measured points onto the design model and display errors with color-coding to visually check construction accuracy. With point cloud data, you can also perform advanced analyses such as deleting unnecessary points and extracting cross-sections, or integrating with the design BIM model to examine consistency in 3D. Because these processed results can be directly reflected in reports and drawings, you can quickly share on-site information with stakeholders and drive improvements in the construction process.

Cloud integration for on-site DX

After importing surveying data into CAD, it is important to quickly share that information among stakeholders. This is where the power of cloud integration comes in. Recent smartphone RTK solutions include features that immediately upload positioning information collected in the field to the cloud, allowing it to be viewed and downloaded from office PCs and other devices. For example, there are services that can visualize measured coordinate points and tracks, captured photos, and generated point cloud data on web map views and 3D viewers, enabling you to grasp the latest situation without being on site.

This cloud integration dramatically advances data consolidation between the field and the office. If a field staff member uploads survey results immediately after measuring, designers and construction managers can verify current site conditions in real time from the office and, if necessary, issue work instructions instantly. Conversely, if the latest drawings and instruction documents are distributed to the field via the cloud, everyone can share the same information without the hassle of delivering paper plans. This two-way information sharing can be expected to prevent rework and reduce communication losses.

Moreover, by accumulating data in the cloud, it becomes easy to refer to past surveying records at any time and to use them as evidence for as-built inspections. This is highly compatible with i-Construction and CIM (Construction Information Modeling) promoted by the Ministry of Land, Infrastructure, Transport and Tourism, and is a factor that strongly supports the digital transformation (DX) of construction sites. By seamlessly connecting the field and the office with digital data, the efficiency and sophistication of the entire construction process are achieved.

The future of simplified surveying realized by LRTK

As we've seen, the integration of RTK technology and CAD software can dramatically streamline surveying and data use on construction sites. Driving this trend further is the smartphone RTK solution LRTK. LRTK is a system developed to transform a smartphone into a "one-device-per-person universal surveying instrument," enabling simplified surveying that combines ease of use with high accuracy. By simply attaching a dedicated compact GNSS receiver to a smartphone, anyone can instantly achieve centimeter-level positioning (half-inch accuracy), and its affordable pricing has led to adoption at many sites.

The benefits of introducing LRTK are substantial, improving on-site productivity and safety. When surveying work that previously required two people can be completed by one, it leads to labor savings and helps address staffing shortages. Being able to survey in real time and immediately utilize the data means work time is greatly reduced, and construction delays and rework caused by waiting for survey results are decreased. Also, finishing surveys in a short time reduces the time workers spend in hazardous areas, contributing to improved safety. On-site feedback has been so positive that people say, "Using LRTK feels like we have twice the manpower," so you can expect to experience a dramatic increase in efficiency.

Going forward, smartphone RTK technology represented by LRTK is expected to become increasingly widespread as a standard tool in the construction industry. The "simple surveying with a tape measure and visual estimation" once used on small sites will be replaced by high-precision simple surveying using LRTK. A future in which anyone can perform high-precision surveys freely with the smartphone in their hand, and that data is instantly reflected in design environments such as CAD software, is becoming a reality. As a solution that opens the way to an era in which contractors themselves can manage and verify sites using digital data, LRTK should become a powerful ally for on-site DX.

FAQ

Q: Can RTK surveying be used by those with no experience? A: Yes. With recent smartphone RTK solutions, surveying can be done through an intuitive app interface, so it can be used even without specialized experience. Traditionally, advanced knowledge such as setting up a base station and radio configuration was required, but with systems like LRTK, surveying is completed simply by following the on-screen instructions. For first-time users, simple training and manuals are provided in advance, so you can start using it with confidence.

Q: Isn't it possible to achieve high-precision positioning with a smartphone's built-in GPS? A: The accuracy of a smartphone's built-in GPS is on the order of several meters (several ft) and does not reach the accuracy required for construction surveying (a few centimeters or less (a few in or less)). RTK secures centimeter-level accuracy (half-inch accuracy) by cancelling errors through corrections from a reference station. For example, a point that would be off by 5 m (16.4 ft) with ordinary GPS can be reduced to an error within a few centimeters (within a few in) when using RTK. This difference in accuracy is critically important when cross-checking against design drawings or performing work that requires strict control of elevation.

Q: Can it be used in mountainous areas where mobile signals do not reach? A: Yes, there are several methods. The latest RTK receivers, including LRTK, support the CLAS signal provided by Japan's Quasi-Zenith Satellite System (Michibiki), allowing them to receive correction information via satellite even in areas outside mobile coverage. In addition, there is an offline positioning mode where base station data is downloaded in advance, and a method of setting up a simple reference station on site for local operation. These approaches mean you don't have to give up high-precision positioning even in environments such as mountainous areas or remote islands.

Q: Can surveying data be utilized even without CAD software? A: It is possible to make use of acquired surveying data even without CAD software. For example, coordinate lists can be exported as CSV files, so they can be opened in Excel or GIS software to check the numbers, and point cloud data in LAS format can be displayed with free point-cloud viewers. Also, by using cloud services that display data on maps, you can share them with stakeholders via a browser and add comments. However, to integrate with design data and perform advanced analysis or produce drawings, it is more efficient to use dedicated CAD software.

Q: What do I need to use LRTK? A: Basically, you can get started with a smartphone or tablet that can connect to the Internet, an LRTK GNSS receiver, and a dedicated app. The LRTK provider will advise on supported OS versions and device models, but it generally works on common smart devices. The app guides you through the initial setup, so there is no complicated work; after mounting the equipment you can begin positioning in a few minutes. A support system is also in place, so you can consult about any uncertainties after deployment and feel reassured.