In civil engineering and surveying, it is required to accurately reflect measured points and terrain information in CAD drawings. However, traditional methods have involved a great deal of labor and time between field surveying and CAD drafting, and there have been challenges in maintaining survey accuracy and transmitting information. This article explains a method to use smartphone RTK surveying—leveraging a smartphone and RTK-GNSS—to process field-acquired data in batch and directly utilize it in CAD drawings with centimeter-level accuracy (half-inch accuracy). Aimed at surveyors, construction managers, CAD operators, and civil design engineers, we introduce the latest efficiency solutions for workflows from field surveying to design drawing creation.

Challenges from traditional surveying to CAD drafting

First, let us review the conventional workflow from surveying to drawing creation. In a typical procedure, a surveyor measures control points and objects on site using instruments such as a transit or a GNSS receiver, and records the results in notes or a data logger. They then return to the office and must input the recorded point coordinates into a computer to create drawings in CAD software. This process involves manual data transcription work, which is cumbersome and time-consuming.

Also, accuracy transfer needs attention across multiple steps. No matter how precisely a site is surveyed, input mistakes or coordinate transformation errors during the process of reflecting those numbers into CAD drawings can undermine the achieved accuracy. Furthermore, when terrain is complex, it takes time to capture detailed as-built conditions in drawings, delaying feedback to designers. Conventional methods required many people and days from surveying to drafting, and coordination between the field and design was often not smooth.

Smartphone surveying with RTK-GNSS and centimeter-level accuracy

A new approach to solve these problems is smartphone surveying using RTK-GNSS. RTK (real-time kinematic) is a technology that dramatically improves GNSS positioning accuracy by using correction information from a base station, reducing GPS position errors that were previously on the order of several meters to a few centimeters. RTK correction information is obtained via the internet through a smartphone app (or by receiving Japan’s QZSS “Michibiki” CLAS signal), improving positioning accuracy in real time. Recently, solutions have appeared that make it easy to use RTK-GNSS on a smartphone. By attaching a dedicated small, high-precision GNSS antenna to a smartphone and receiving RTK corrections, a smartphone can achieve centimeter-level positioning (half-inch level accuracy).

Traditionally, high-precision surveying required total stations or large GNSS equipment, but smartphone RTK surveying turns everyday smartphones into surveying devices. Built-in smartphone GPS typically has errors on the order of 5-10 m (16.4-32.8 ft), but by using an RTK-capable GNSS antenna and app, the current location can be measured with astonishing accuracy of ±1-2 cm (±0.4-0.8 in) in plan and about ±3-4 cm (±1.2-1.6 in) in height. For example, it supports coordinate systems and geoid heights used in Japanese public surveys, and positioning results can be directly applied to the design drawing coordinate system. With the ability to obtain centimeter-level position information on a smartphone, workflows from field surveying to CAD conversion are beginning to undergo major changes.

Procedure for point-cloud measurement and single-point positioning with a smartphone app

With smartphone RTK surveying, dedicated smartphone apps enable acquisition of 3D field data. One method is point-cloud measurement. By using a smartphone camera or LiDAR scanner to scan surrounding structures and terrain, you obtain a large set of points (point cloud data). Because the smartphone’s position is continuously determined with high accuracy via RTK-GNSS, real-world coordinates are assigned to all acquired points. As a result, even complex terrain can be captured by walking around the site while performing a 3D scan, producing a high-accuracy point-cloud model with each point correctly placed in global coordinates (survey coordinate system). Unlike conventional laser scanners, no special equipment or post-processing for point-cloud alignment is required, and a single smartphone can easily capture detailed as-built shapes.

Another basic feature is single-point positioning. This measures the coordinates of an arbitrary point accurately by using the RTK-GNSS receiver attached to the smartphone and performing positioning over the point of interest. For example, if you want to measure a point on the ground or the location of a structure, simply align the smartphone over that point and press a button to instantly obtain latitude, longitude, and height information. In the app you can name and attach notes to measured points and save them; time and RTK status (whether a Fix solution was obtained) are also recorded. If necessary, you can average several seconds of measurements to further improve accuracy to the millimeter level (0.04 in) easily, enabling stable high-precision positioning even by a single person. By fixing the smartphone and receiver on a dedicated monopod (pole) and aligning the tip to the survey point, stable measurements are possible; the app automatically corrects for height offsets. Observational tasks that previously required skill can now be performed efficiently by anyone following the smartphone app’s guidance, allowing coordinate acquisition for points without specialized expertise.

Output of smartphone surveying data and CAD integration flow

Survey data acquired on site with a smartphone can be smoothly linked to CAD. Coordinate data recorded by the smartphone app can be uploaded to the cloud or exported as files with a single tap. For example, a list of measured points can be exported in CSV format; importing that CSV file containing point names and coordinates (X, Y, Z) into CAD or surveying software will plot the measured points on the design drawing. Point-cloud data measured on site can also be downloaded via the cloud and converted into files such as DXF or LAS that CAD and 3D software can handle. Since data from smartphone RTK surveying are positioned in public coordinate systems from the start, if the design drawing uses the same coordinate system they can be overlaid precisely without special adjustment. In this way, the workflow to directly import field data as digital data into CAD is becoming established, eliminating the manual effort of drafting data collected in the field.

As-built verification by overlaying point clouds and CAD drawings

High-precision point-cloud data acquired with smartphone RTK can be easily overlaid and compared with design CAD drawings or 3D models. For example, by scanning the existing terrain as a point cloud before construction and overlaying that data onto the design 3D model, you can confirm in advance how the planned structure will fit the actual terrain. When checking as-built conditions during or after construction, scanning the site and overlaying the resulting point-cloud model with the as-built or design data makes it immediately apparent whether construction is progressing according to design. Point clouds and measured points acquired by smartphone RTK share the same survey coordinate system as design drawings, so they automatically align spatially when loaded into software. Previously, matching field survey data to drawings required manual alignment or the use of specialized analysis software. With this process digitally integrated, discrepancies in as-built conditions can be quickly detected in CAD and used for quality control. The Ministry of Land, Infrastructure, Transport and Tourism also recommends the use of 3D point clouds in as-built management, and as-built verification using point-cloud data acquired by smartphone RTK conforms to the latest quality management standards.

Visualizing construction errors with heat maps

By comparing point clouds with the design model, quantitative differences can be analyzed. For example, calculating height differences between the existing ground and the design model at each point and visualizing them with a color gradient creates a heat map that intuitively shows where discrepancies from the design are greatest. In earthwork such as embankment and excavation, this heat map makes it obvious “where to excavate how many more centimeters” or “where too much fill has been placed,” helping prevent rework. Furthermore, automatic volume calculation from differences between the point cloud and design data is possible, greatly streamlining daily quantity calculations for as-built management. Combining smartphone RTK with point-cloud technology enables such advanced analyses to be performed immediately on site, dramatically improving the speed and accuracy of construction management.

Projecting design data onto the site with AR

A distinctive function of smartphone RTK solutions is AR (augmented reality) projection of design data onto the site. Through a smartphone screen, you can overlay a 3D model so that it appears as if the completed structure or guide lines already exist on site. In conventional AR, misalignment was an issue, but high-precision RTK positioning enables digital models to be projected onto their actual coordinate positions with negligible offset. For example, overlaying a 3D CAD model of a planned bridge or retaining wall on-site allows designers and construction staff to conduct meetings while sharing the completed appearance. It is also possible to place virtual AR stakes at control points or pile-driving positions from drawings, enabling positioning checks even in complex terrain or areas difficult to access physically. As workers walk around the site, RTK continuously corrects their location so the AR display does not drift, allowing anyone to intuitively verify the design image in space. High-accuracy AR visualization helps all stakeholders—clients and construction teams alike—share the same completion image on site, reducing misunderstandings and smoothing pre-construction coordination.

Rapid feedback between design and field through cloud sharing

Smartphone RTK surveying leverages cloud-based data sharing to dramatically improve communication between design and the field. Traditionally, delivering field-measured data to designers required time-consuming steps such as drafting drawings and emailing them or bringing files back on USB drives. However, positioning information collected by the smartphone app can be synchronized to the cloud in real time, allowing designers in the office to immediately review field survey results. For example, if unexpected obstacles are encountered on site, survey data and photos can be shared via the cloud on the spot, and designers can promptly revise drawings and provide feedback. Conversely, when revised design data (such as updated drawings or 3D models) are uploaded to the cloud, they are immediately synchronized to smartphones on site so work can proceed based on the latest design information. By utilizing cloud integration, two-way information sharing between the field and design becomes seamless, significantly accelerating decision-making and response times. In addition, 3D viewers hosted in the cloud allow stakeholders and subcontractors who receive a shared link to inspect point-cloud and measured-point data in a browser without special software.

Benefits of field-completed batch processing

As described above, a one-stop workflow centered on smartphone RTK is taking shape, enabling end-to-end processing in the field. Finally, let us summarize the main benefits this batch processing brings to site operations.

• Labor reduction: One person can manage everything from surveying to drawing creation, enabling personnel reductions and simplifying staffing. Tasks that previously required multiple people for observation and instrument operation can be completed with just a smartphone and auxiliary equipment.

• Avoiding dependence on individuals: Without relying on special skills or experience, anyone can perform surveying and data processing following standard procedures, reducing the risk of work concentrating on specific personnel and making it easier for the organization to share and utilize data.

• Speed-up: Because field-acquired information is digitized on the spot and shared via the cloud, CAD drawings can be updated and as-built conditions checked on the day of surveying. Processes that used to take days are drastically shortened, shortening the overall construction cycle.

• Accuracy maintenance: By processing measured point data digitally from the outset, manual entry errors and conversion errors are minimized. Centimeter-level information obtained on site can be directly reflected in drawings and study materials, contributing to quality assurance.

As described above, one-stop processing using smartphone RTK greatly improves efficiency and sophistication in surveying and design workflows. The ability to handle accurate data quickly from the field is a significant advantage in the era of construction DX.

Utilizing the smartphone RTK solution "LRTK"

Finally, as a concrete solution to realize the workflow described above, we introduce "LRTK." LRTK is a surveying solution composed of an ultra-compact RTK-GNSS receiver that integrates with a smartphone, a dedicated app, and cloud services. By simply attaching the dedicated device to the back of a smartphone, an iPhone or iPad is transformed into a centimeter-accurate positioning terminal. LRTK’s positioning accuracy is high, within approximately horizontal ±2 cm (±0.8 in) and vertical ±4 cm (±1.6 in). In addition to network-based corrections, it supports CLAS satellite augmentation signals provided by Japan’s quasi-zenith satellite Michibiki, enabling stable centimeter-level positioning (half-inch level accuracy) even in sites with poor communications. This single unit supports everything from single-point positioning to 3D point-cloud scanning, pile position guidance, and AR display of design data, and the acquired data can be uploaded to the cloud immediately for sharing with stakeholders. Despite being specialized equipment, its pocketable, lightweight size makes it easy to take out and use during site work. It has already attracted attention among construction managers and surveying technicians and is beginning to contribute to productivity improvement on site as an all-purpose surveying tool for one device per person.

By adopting LRTK, a smartphone RTK solution, you can realize the field-to-CAD batch processing described above. It fundamentally streamlines the previously complex workflow and enables accurate data acquisition and utilization even by non-specialists. If your company is considering efficiency improvements from surveying to design, consider introducing LRTK, the latest smartphone RTK solution. The innovation of surveying with smartphone RTK is expected to remove barriers between field and office and significantly contribute to improved productivity on construction sites. Ride this wave and further advance your company’s site DX.