Thorough Comparison: Traditional Cross-Section Creation vs. Using LRTK — How Do Accuracy and Time Change?

Importance of Cross-Section Creation and On-Site Use Cases

In civil engineering and construction sites, creating cross-sections of the terrain and structures is indispensable. A cross-section is a depiction of a vertical cut through the ground surface or a structure, allowing intuitive understanding of elevation differences and subsurface shapes. For example, in road works, longitudinal and transverse cross-sections along the route are used to plan cut-and-fill and to check as-built conditions. In river and levee maintenance, river cross-sections are measured periodically to monitor sedimentation and erosion. In building and land development, cross-sections showing excavation shapes of foundations are created to ensure consistency with design and for safety checks. In this way, creating cross-sections is an important task widely used from the design stage through construction management to final inspection.

However, accurate cross-section creation requires surveying work on site, which has traditionally taken considerable time and effort. When terrain is complex or the survey area is large, it is not easy to measure all required points without omission. Recently, with the spread of 3D design and as-built management, more detailed and higher-density survey data have been demanded. In that context, the use of new surveying technologies has begun to dramatically improve the efficiency and accuracy of cross-section creation. This article thoroughly explains the differences in accuracy and time between traditional methods of cross-section creation and methods using the latest 3D surveying solution, LRTK.

Traditional Cross-Section Creation Methods and Challenges

Traditionally, surveys for creating cross-sections on site have been conducted using dedicated instruments such as levels and total stations. A typical procedure is as follows.

• Survey preparation: Confirm known reference points and benchmarks, and mark the cross-section line and surrounding area (layout marking). Decide where to set up the surveying instrument, mount it precisely on a tripod, and perform initial setup.

• Field measurement: Along the survey line, at regular intervals or at terrain change points, a staff (rod) or prism is set up and another worker sights and reads with the surveying instrument. Heights and distances of each point are measured sequentially and recorded in notes or field books. If necessary, the instrument is moved and reinstalled (leapfrogging) to cover the entire cross-section line.

• Drafting: Bring the measured point data back to the office for organization and calculation. Determine each point’s elevation from height differences and create transverse and longitudinal cross-section drawings using CAD software, etc. Annotate ground and structure elevations at important locations and compare with design cross-sections to check for discrepancies.

This series of tasks typically requires two or more people, and the more measurement points there are, the greater the effort. When measuring multiple cross-sections over a wide site, including the time to relocate instruments and post-processing, it is not uncommon for the work to take an entire day. Furthermore, when converting field-acquired data into drawings, manual transcription and calculation are involved, so the data cannot be utilized in real time. The traditional human-dependent approach also carries unavoidable risks of human error such as reading mistakes and recording errors. In fact, overlooked points or incorrect data entries have led to inconsistencies on drawings discovered later, causing re-surveying (rework). Relying on a small number of highly skilled surveyors also creates personnel-dependent issues—work may stall when the responsible person is absent. Although traditional cross-section creation methods are established and reliable, labor and time costs and inefficient data utilization have been major challenges.

Cross-Section Creation Using 3D Surveying with LRTK

The recently introduced LRTK (a positioning system that makes high-precision GNSS easily usable with a smartphone) is poised to significantly change cross-section creation methods. LRTK attaches a compact RTK-GNSS receiver to a smartphone or tablet and corrects satellite positioning errors in real time, enabling centimeter-class high accuracy (cm level accuracy (half-inch accuracy)). No specialized equipment or large-scale setup is required; an ordinary smartphone effectively becomes a precise surveying instrument.

The workflow for cross-section surveying using LRTK is simple. As an example, the work can be completed in the following flow.

• Setup: Attach the LRTK receiver to a smartphone and launch the dedicated app. Positioning information from satellites is automatically corrected so that positions can be determined with accuracy on the order of a few centimeters (a few in) (reference-station data or satellite augmentation signals are received via the network).

• Surveying and point cloud acquisition: An operator walks along the desired cross-section line alone, recording survey points with the smartphone. If necessary, the smartphone’s built-in LiDAR scanner or photo functions can be used to capture surrounding 3D data (point clouds). By recording terrain undulations and structure shapes as high-density point cloud data, cross-sections can later be extracted at arbitrary locations.

• Data verification and drafting: Field-acquired data are visualized in real time on the app. Cross-sections can be displayed on the smartphone immediately after measurement so that elevations and positions of each measured point can be checked on the spot. With one touch, data can be uploaded to the cloud, enabling detailed analysis and drawing creation on office PCs and easy sharing with stakeholders. The system also includes functions to automatically generate cross-section lines from acquired point cloud data and output drawings in formats usable by CAD software.

By using LRTK in this way, cross-section surveying can be completed by one person, and results can be confirmed on site, reducing the likelihood of rework. Advanced settings and calculations are handled automatically by the device, so even technicians with limited surveying knowledge can operate it intuitively. Tasks that used to rely on the experience of skilled personnel are now automated by the app performing elevation calculations and coordinate transformations, ensuring consistent accuracy regardless of who measures. Measurement data are digitized instantly, eliminating the need to transcribe onto paper and greatly reducing concerns about human error. This is truly a new cross-section creation method that promotes on-site DX (digital transformation).

Accuracy Comparison (Point Density, Coordinate Reliability, Reproducibility)

Differences in the accuracy and reliability of survey data obtained by traditional methods and by using LRTK also become apparent. Let’s compare from each perspective.

• Point acquisition density: In traditional cross-section surveys, points are measured every few meters (every few ft) or at terrain change points. The number of points that can be measured is limited by available personnel and time, and fine undulations may not be captured. In contrast, LRTK enables easy acquisition of high-density point cloud data. Because points can be recorded continuously while walking and LiDAR scanning can capture surfaces, even subtle terrain undulations can be reproduced. The denser the point distribution, the more the cross-section reflects the actual terrain in detail.

• Coordinate reliability: Traditional surveying instruments (total stations and levels) can measure with extremely high local accuracy (millimeter-level (mm level; 0.04 in)), but errors propagate when distances from reference points increase or when the instrument is repositioned multiple times. Additionally, separate calculations or transformations are needed to align acquired data with known coordinate systems. With LRTK, absolute coordinates from GNSS are obtained on site, allowing measurement points to be recorded directly in nationwide coordinate systems (such as plane rectangular coordinate systems). Errors are generally contained to a few centimeters (a few in), which is sufficiently reliable for cross-section creation. The fact that accuracy is consistently maintained regardless of the surveyor’s skill level is also reassuring for on-site work.

• Reproducibility: With traditional methods, if a different person measures the same cross-section on another day, differences in which points are selected and reading variations can lead to inconsistent results. Especially, how much of intermediate terrain changes are captured depends on subjective judgment, so repeated measurements may not yield the exact same cross-section shape. In contrast, if terrain is captured as a point cloud with LRTK, the same data tend to be obtained regardless of who performs the measurement. Once a point cloud is acquired and stored digitally, extracting the same cross-section line later will yield identical results. In other words, LRTK’s method excels in terms of data acquisition reproducibility and consistency.

Comparison of Work Time, Rework, and Risk of Missing Measurements

From an efficiency viewpoint, there are large differences between traditional methods and LRTK. Compare several points below.

• Work time: Traditional cross-section surveying inherently takes time from equipment setup through field measurement to pack-up. The more points to measure, the longer it takes, and sometimes the work cannot be completed in a single day. Using LRTK, surveying and drafting processes are seamlessly linked, substantially shortening the overall work time. Field measurement itself is efficient, and one person can cover a wide area in a short time. For example, transverse surveys that used to take half a day can, in some cases with LRTK, be completed in only a few minutes.

• Occurrence of rework: The traditional method always carries the risk of re-surveying due to insufficient data or mistakes. If additional measurements are needed after returning to the site, personnel must be arranged to go out again, which is inefficient. With LRTK, detailed data are acquired from the start, making it less likely to forget to measure a spot later. If an omission is noticed, one person can quickly go to the site and perform additional measurements, enabling rapid recovery. As a result, the risk that surveying work will cause schedule-impacting rework is reduced.

• Risk of missing measurements: In complex terrain, traditional methods tend to result in missed measurements. Because point selection is based on visual judgment, unexpected depressions or local hollows can be overlooked. With point cloud measurement using LRTK, nearly all visible ground surface information can be captured without omission. Fewer gaps mean that when drawings are created later, issues like “this part has no data” are less likely to occur. Reduced concern about data omission increases confidence in survey results.

Data Usability Comparison (Cloud Sharing, Design Comparison, Deliverable Output)

There are also major differences in how survey data can be used between old and new methods. Here we compare data sharing, comparison with design, and deliverable creation.

• Cloud sharing: In traditional surveying, data are typically handed over as paper drawings or via USB drives, making real-time information sharing difficult. With LRTK, measurement data can be uploaded directly to the cloud from the field, allowing office staff and clients to share immediately. For example, if cross-section data are shared via the cloud right after measurement, stakeholders in remote locations can review the same cross-section and discuss it. Since everyone can act on the latest information, decision-making speed increases.

• Comparison with design data: Traditionally, comparing surveyed results with design cross-section shapes required visually aligning printed drawings or overlaying them in CAD, which made error detection and as-built evaluation time-consuming. LRTK solutions allow pre-uploaded design cross-section data or 3D models in the cloud to be overlaid with field-acquired point cloud data. This enables verification of differences between design lines and measured data on site, allowing immediate decisions about whether additional excavation is needed or if embankments conform to design. For as-built inspections, differences between LRTK-measured cross-sections and design values can be automatically calculated in software, producing objective verification materials.

• Deliverable output: Creating deliverables such as drawings and data for submission can also be streamlined with LRTK. Traditionally, a CAD operator manually drew cross-section lines from point clouds. LRTK can automatically generate cross-sections from acquired point clouds and measurement data and output them in formats such as DXF or LandXML. These outputs can be used directly for deliverable drawings, greatly reducing the drafting workload. Point cloud data themselves can be stored and submitted as 3D models, making them easy to use for future design changes or additional analyses. The ease of storing and reusing digital data is a major advantage for future information-driven construction.

Ease of Use for Small Sites and Non-experts

The LRTK-based cross-section creation method is so easy to use that it offers significant benefits for small sites and non-expert surveyors. Surveying work that used to require hiring professional firms can now be performed in-house with ease.

• Simplicity of equipment and operation: A smartphone and a small receiver are enough; no large special equipment is needed, and transporting equipment to the site is simple. The app’s operation is straightforward—follow on-screen instructions and the survey is completed. Complex surveying calculations and coordinate transformations are automated, so accurate results can be obtained even without specialized knowledge.

• One-person operation: On small sites with labor shortages, two people may not be available for surveying. LRTK allows one person to complete the work, freeing other workers and enabling flexible scheduling—measurements can be done quickly when needed, which is a major operational advantage.

• Reduced introduction and operating costs: The burden of purchasing expensive surveying instruments or repeatedly hiring external contractors is reduced. Even small projects can achieve cost-effective high-precision surveying with LRTK, enabling measurements that were previously omitted to be undertaken proactively. This leads to improved safety and quality control.

• Immediate data utilization: For non-experts, making use of measured data can be a concern, but LRTK addresses this. Data accumulated in the cloud are automatically organized, and required cross-sections and values can be retrieved immediately. Generating drawings for reports is completed with button operations, so appropriate outputs can be obtained without specialized knowledge.

Conclusion: Innovations Brought to the Field by LRTK’s Quick Surveying and Cross-Section Generation

We have compared traditional cross-section creation with methods using LRTK, and LRTK’s usefulness stands out in both accuracy improvement and time reduction. High-density data acquisition and immediate drafting that were difficult to achieve with human-dependent surveying are now possible for anyone with LRTK. This not only reduces the burden of measurement work on site but also increases the reliability of the resulting cross-sections.

By leveraging LRTK’s quick surveying and cross-section generation functions, reliable cross-section creation can be performed without relying on veteran technicians, directly improving on-site productivity. Significant effects are also expected in reducing rework and smoothing data sharing—issues that have been problematic with traditional methods. Consider introducing LRTK as a next-generation solution that promotes on-site DX while balancing efficiency and quality. The adoption of new technology will bring innovation to cross-section creation on site and, in turn, contribute to the overall smartification of construction.