How to Create RTK-Compatible DXF Data｜Practical Workflow from Surveying to Drafting

Table of Contents

• Introduction

• What Is RTK Surveying?

• Survey Preparation and Planning

• Field RTK Survey Procedures

• Organizing Survey Data and Coordinate Adjustment

• Creating Drawings in CAD Software and DXF Export

• Key Points and Challenges in the Practical Workflow

• Conclusion: Using the New Tool LRTK to Improve Accuracy and Efficiency

Introduction

In on-site work such as civil engineering design, land development, pile-driving (survey staking) operations, boundary surveying, and verifying building positions, it is important to accurately convert surveyed data into drawings. In recent years, high-precision GNSS surveying using the RTK (Real-Time Kinematic) method has become widespread, allowing coordinates acquired on-site to be directly reflected in CAD drawings. RTK-compatible DXF data refers to DXF-format drawing data created based on on-site coordinates obtained by RTK surveying, with design drawings and topographic maps drawn to match the actual geodetic coordinate system. This article explains in detail the practical workflow from field surveying using RTK-GNSS to converting that data into DXF-format drawings. The explanation is given independently of specific software or equipment types, describing on-site procedures and points to watch so you can use it to produce highly accurate drawings.

What is RTK surveying?

RTK surveying is a method that corrects GNSS (satellite positioning) measurement errors in real time to achieve centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)). Ordinary GPS positioning can have errors of several meters (several ft), but RTK combines a base station (base) and a mobile station (rover) and improves accuracy by exchanging via communication the differences between the satellite signals received at both. As a result, horizontal positions can be obtained on-site immediately with an accuracy of several centimeters (several in), and elevations with an accuracy of several centimeters to several tens of centimeters (several in to several tens of in). This high-precision real-time positioning has made it possible to replace fine surveying tasks that were traditionally performed with total stations with GNSS, and to reflect survey data directly into CAD drawings.

To perform RTK surveying, a set consisting of a GNSS receiver for the base station and a GNSS receiver for the rover is typically used. The base station is installed at a known, precise position and generates correction information based on that coordinate. The rover observes survey points while moving around the site, receives correction information sent from the base station, and computes its own position. In recent years, network RTK using mobile communication networks (reference station network services) has also been developed so that even without installing your own base station, you can receive correction data distributed from surrounding electronic reference points on a smartphone or similar device and perform centimeter-level positioning (half-inch accuracy). In either method, if operated properly you can obtain high-precision survey point coordinates that directly correspond to the site’s surveying coordinate system, and using these in CAD software enables drawings with no "misalignment."

Survey Preparation and Planning

Accurate RTK surveying requires preparation and planning before entering field work. First, confirm the coordinate system and reference to be used for the project. For surveying work in Japan, official coordinate systems such as the plane rectangular coordinate system zone ○ of the World Geodetic System (JGD2011, etc.) are often used. If the client or the design drawings specify a reference coordinate system, identify it in advance and plan so that the same coordinate system can be adopted for field surveying. Investigate whether there are known control points near the site (triangulation points, electronic reference points, public coordinate benchmark stones, etc.), and if available obtain their coordinate values. Even if no control points can be found, consider use of network RTK described below or methods for local coordinate adjustment by matching with existing maps. Agreeing on a common coordinate reference among project stakeholders in advance is very important to facilitate smooth data interoperability in later stages.

Next, prepare the equipment you will use. Bring to the site a full set of RTK-GNSS receivers (for the base station and the rover), data-collection terminals (dedicated controllers, tablets, smartphones, etc.), communications equipment (radios and mobile routers), tripods and poles, spare batteries, and so on. Before departure, thoroughly check battery charge levels and prepare additional batteries as necessary. Also check that the receivers and the firmware/software of any applications you will use are up to date and stable. In addition, configure and test the communication method between the base and the rover in advance. If using radios, match the frequency and channel settings; for network RTK, register connection information such as Ntrip on the terminal and complete communication tests in the office for reassurance. By carrying out these preparations carefully, field surveying work will proceed smoothly and accuracy and efficiency will be ensured.

On-site RTK Survey Procedures

Installation of base stations and setting of reference coordinates

When you arrive on site, first install the base station (base station). Look around and choose a stable location where the sky is wide open and there are few buildings or trees that would block the view overhead. Set up a tripod and mount the receiver, use a level to adjust the antenna so that it is vertical, and secure it firmly. After installing the base station, decide how to set its reference coordinates. The typical methods are as follows.

• Method of installing on a known point: This is a method of placing the base station on a control point whose accurate coordinate values (latitude/longitude or planar coordinates) have been determined in advance. That known coordinate value is set as the base station's position as-is. Doing so ties the survey results directly to the existing geodetic datum, so when the data are later placed on CAD drawings there will be no coordinate displacement. This is the most reliable method, but it is applicable only when a suitable control point exists on site.

• Method of averaging positioning on site: When there is no official control point near the site, this method installs the base station at an arbitrary location and sets the base station's position to the averaged coordinate value obtained by performing GNSS observations at that location for a few minutes (commonly called "survey-in"). You can establish a reference coordinate in a short time, but the absolute accuracy of that coordinate itself may include errors on the order of several meters (several ft). However, because the relative positioning accuracy between the base station and the rover is maintained, this method still poses no problem for dimensional measurements within the site. It is used as a provisional reference on the assumption that an adjustment to align with an absolute coordinate system will be made later.

• Method of matching a local coordinate system: If the construction site already has its own local coordinates (for example, an arbitrary coordinate system on the design drawings), this is the technique of aligning observational values to that coordinate system. First, install the base station at an arbitrary point, run RTK, and obtain provisional survey coordinates. Next, observe on site with RTK the known points on the existing drawings (for example, stakes whose coordinate values are given on the design drawings), calculate the offsets between the obtained survey coordinates and the coordinates on the drawings to determine correction values. Apply these as a local transform to the base station coordinates and survey points to make the survey data match the project's local coordinate system. The procedure is somewhat complex, but it is effective for ensuring consistency with existing drawings.

Whichever method is used, be sure not to forget to enter the base station’s antenna height. Precisely measure the height from the base station’s antenna reference point to the installation surface (the ground or a marker such as a nail), and enter it into the controller. Be careful when entering the antenna height, as incorrect input particularly affects vertical accuracy. After the base station installation and configuration are complete, switch it to the mode that transmits correction information. For radio communication, match the frequency and channel with the rover and transmit the signal; for network-based delivery, start Ntrip streaming. Once the base station is operating normally and begins providing real-time correction data, move on to preparing the rover for observation.

Survey Point Observations and Surveying and Setting-out Operations at Mobile Stations

The receiver at the rover (mobile unit) is typically mounted on and carried with a pole or staff. Before starting surveying, use the pole’s bubble level to confirm the antenna is vertical and enter the antenna height accurately. Once ready, begin observations at the rover, receive correction data from the base station, and perform RTK positioning.

First, as a baseline check, observe a few known points or clearly defined points near the base station and confirm whether the coordinates obtained are as expected (even when using network RTK, it is reassuring to measure known points and check the error relative to the published coordinates). If there are no problems, proceed to observe the planned survey points.

In topographic or as‑built surveys, the features or terrain points you want to survey are observed sequentially with a rover. When recording survey points, ensure accuracy by stabilizing the positioning for each point before pressing the record button, or by taking an average over a set period. When measuring a wide area, it is also effective to use the controller's "continuous measurement mode" (topographic surveying mode) to automatically acquire points at regular intervals while walking. If you record points with codes or notes so they are easy to identify later, office drafting work becomes easier (e.g., "BM1" = benchmark, "CL" = point on the centerline). For important points, measure them twice as a precaution and check them on a sketch to avoid any omissions.

In stakeout and setting-out operations, the work is reversed: you guide the rover in the field to the target points' coordinates specified on the design drawings. RTK-capable controllers can preload design coordinate data extracted from CAD drawings, and when a target point is selected they display in real time the offset between the current position and the target point (e.g., "east by 5 cm (2.0 in), north by 3 cm (1.2 in), up"). By using this, even a single operator can determine accurate stake positions by following the on-screen instructions. For important building layout points and boundary stake installation, you can mark the site at the exact coordinates from the drawings, enabling accurate layout work with no need to redo steps. This assumes that the coordinates obtained by surveying and those on the design drawings are aligned to the same reference; however, if the coordinate system is consistently unified from RTK surveying through to DXF drawings, such setting-out operations can be carried out smoothly.

After finishing observations of the planned survey points on site, we carry out a verification check as a precaution. We measure known distances between multiple survey points to confirm any errors, and re-observe known control points to check whether there are any shifts in coordinates. If everything is fine, the on-site RTK surveying work is complete. We dismantle the rover equipment and take the recorded survey data back with us.

Organization of Survey Data and Coordinate Adjustment

When you return to the office (or even to your vehicle on site), organize the data obtained with RTK and prepare it for drafting. Export the coordinate data of the survey points from the rover controller or the data collection terminal. Generally, output them as a point coordinate list in CSV or text format, and in some cases there are instruments or apps that can export directly in CAD-compatible DXF/DWG format. The exported data contains each point's ID, coordinate values (X, Y, Z), and codes or attributes.

Next, adjust the coordinate system of the survey data to match the final drawing. If the base station was set on a known point or observations were made using network RTK, the acquired coordinates are already in the intended geodetic datum. If you plot them directly in the CAD drawing, there should be no discrepancy with the design drawings. On the other hand, if the base station coordinates were assumed in the field (e.g., average positioning) or if you need to fit the data to a project-specific local coordinate system, perform the coordinate transformation at this stage. Specifically, compute the differences between the surveyed control points or known points and their target coordinates in the desired coordinate system, then apply a bulk translation (and, if necessary, rotation and scale adjustments) to all measured points. Most surveying-specific software includes coordinate transformation tools that automatically compute the corrections when you input two or more pairs of corresponding coordinates. Even if done manually, it is not difficult to apply the corrections in Excel by simply adding or subtracting ΔX・ΔY・ΔZ. When aligning data to drawings that use a different coordinate system than the one used during surveying, be sure to carry out this transformation process to unify the site coordinates with the design drawing coordinates.

Care should also be taken with height (Z coordinate). GNSS elevation values are called ellipsoidal heights and differ from the more commonly used mean sea level–based heights (e.g., altitude above sea level). By using the geoid model published by the Geospatial Information Authority of Japan, you can determine this deviation (geoid height) and derive the elevation (orthometric height) from GNSS measurements. For example, by applying corrections using the values from the Geoid of Japan 2011 (GSIGEO2011), it is possible to adjust the heights of the acquired points to the height system of the Public Survey standards. Because height reference is also important for land development work and verification of building heights, this conversion should be carried out as needed.

At the end of organizing the data, also perform a quality check on the survey points. Remove or edit any points that are clearly erroneous or duplicated from the list. Group coded points by their code to make subsequent drafting more efficient. Once you have prepared up to this point, you can move on to creating drawings in CAD software.

Creating Drawings and Exporting DXF with CAD Software

Import the organized survey coordinate data into CAD software and create a DXF drawing. In many cases, to plot (place) point data in CAD you use functions to import point cloud data or a coordinate list, or to load them as external references. As a simple method, you can create a text script from a CSV coordinate list and use a procedure that automatically places point objects in CAD. In any case, once each surveyed point is placed at its accurate coordinates on the CAD drawing, the figure below is complete.

Next, draw the necessary lines and shapes based on the plotted survey points. If the deliverable is a topographic survey, connect points for each feature to create polylines and polygons. For example, draw a road edge line through the points measured along the roadside, and if you measured a building’s perimeter points, join them to depict the building outline. If you assigned codes during surveying, there are CAD programs and plugins that automatically connect points by corresponding code to generate breaklines (polylines). Using those can automatically create lines in the order measured, greatly reducing effort. Even without codes, manually drawing lines based on field sketches and point names noted on site is fine.

It is also possible to generate contour lines and cross-sectional profiles from survey data. When there are many terrain points with elevation values, you can build a TIN (triangulated irregular network) using CAD or surveying calculation software and automatically draw contour lines to produce a topographic map. For important structures, you can create longitudinal and cross-sectional profiles and plot the cross-sectional shapes from the heights of the surveyed points. For example, if you derive cross-sections of ground elevations along a road centerline from RTK survey data, you can calculate the difference from the design elevations and use that to inform construction planning.

The finished drawing data can be used as an "existing conditions map" or an "as-built drawing" that faithfully adheres to the original survey coordinate system. If existing design drawing data is available, it is also easy to overlay and compare them on the same coordinate system. In boundary survey cases, you can overlay cadastral maps or drawing data of adjacent properties to check for shifts in boundary points, and in building as-built drawings you can scrutinize the relationship between site boundary lines and building positions—verification tasks that become possible precisely because of the unified coordinate system.

Finally, export the CAD data you created to DXF format. DXF (Drawing Exchange Format) is an industry-standard CAD data exchange format that is widely supported across software types and versions. By saving in DXF, recipients can open the drawings with free CAD viewers even if they do not have commercial software, enabling smooth information sharing among stakeholders. For electronic delivery to clients, DXF drawings are easy for the recipient to handle and provide peace of mind in terms of compatibility. In recent years, electronic submission of drawing and coordinate data has become mainstream, and it is increasingly common to submit surveying results as drawings in a DXF file or to attach a CSV list of point coordinates as supplementary material. Compiling deliverables in these common data formats also creates asset data that is easy to reuse in the future.

Key points and challenges in the operational workflow

The above describes the overall process from surveying to drafting, but there are several practical points to note. First, consistent coordinate management. From the surveying stage through CAD drawing creation, using the same reference coordinate system at all times prevents discrepancies between the site and the drawings. If it becomes necessary to convert to a different coordinate system partway through, always perform the conversion with appropriate calculations and take care that the positional relationships of points do not change. Especially in projects involving multiple teams or external contractors, it is important to clarify and communicate the coordinate system arrangements in advance.

Accuracy control and verification are also indispensable. RTK surveying is convenient, but there are risks of satellite signal interruptions and errors caused by multipath (radio wave reflections). For surveys of boundary points and important structures that require high precision, it is recommended to perform double checks, such as verifying RTK results with a total station. For vertical measurements as well, supplement with leveling where necessary and confirm height differences from official benchmarks to enhance reliability. Professionals do not rely solely on GNSS data obtained in the field; they identify and correct errors by comparing with known points and by cross-checking using multiple methods.

In terms of personnel and work efficiency, the use of RTK technology is expected to reduce labor in surveying operations. Tasks that traditionally required a survey team can be carried out with a small number of people (in some cases a single person) with RTK. However, because knowledge of equipment handling and setup is necessary, it is advisable to undertake prior training and pilot operations before performing actual work. Workflows that share data via the cloud and enable real-time feedback between the field and designers are also being developed. For example, if point cloud data measured on the same day can be sent to the office via the cloud and the design department can immediately begin drafting and review, it would greatly shorten the time required. As DX (digital transformation) advances, how to accelerate the transfer of information from surveying to design will also be a future challenge.

Conclusion: Leveraging the New Tool LRTK to Enhance Accuracy and Efficiency

We've reviewed the workflow and key points from RTK surveying to DXF drafting, and in recent years new solutions have emerged that further simplify and accelerate this process. One of these is LRTK, a high-precision GNSS receiver device. LRTK is designed so that a compact RTK-GNSS unit can be attached to a smartphone such as an iPhone, and when paired with a dedicated app it enables anyone to easily achieve centimeter-level positioning (cm level accuracy, half-inch accuracy). For example, by simply attaching LRTK to a smartphone and walking around a site, you can scan the surrounding terrain and structures to generate point cloud data and assign high-precision position coordinates to each point. The collected data is automatically processed in the cloud, and with the push of a button plan views and cross-sections can be downloaded instantly as DXF files. This drastically reduces the previously required complex point cloud processing and manual drawing tracing, making it possible to obtain deliverable drawings from the field in a short time.

Introducing modern tools like LRTK can make the workflow of RTK surveying and drafting much more seamless. High-precision positioning information can be obtained on-site in real time, and because it automatically proceeds to CAD drafting via the cloud, it enables both improved accuracy and increased work efficiency. It is also effective as a surveying and drafting tool that a single person can operate, addressing challenges such as labor shortages and a decline in skilled personnel. Of course, it is necessary to use traditional methods as appropriate for site conditions, but it has attracted attention as an option that dramatically simplifies the process of creating RTK-compatible DXF data. Please make use of it for creating accurate and easy-to-understand drawings while incorporating surveying technologies that will continue to evolve.