RTK→GIS: How to Deliver Field Assets Accurately with Attributes

Table of Contents

• Introduction

• What is RTK?

• GIS and Attribute Information of Field Assets

• Procedure for Surveying Field Assets with RTK

• Key Points for Accurate Delivery

• Simple Surveying with LRTK

• FAQ

Introduction

Have you ever measured the locations of infrastructure assets in the field using high-precision GNSS (RTK), only to find the resulting data misaligned on the GIS or missing attribute information? Without correctly recording attribute information such as equipment type or ID along with high-precision positional data, the data cannot be effectively used on maps later.

Also, if differences in coordinate systems or geodetic datums are left unaddressed, measured points may not match drawings or existing data, potentially causing serious mistakes and rework. To prevent these problems and accurately hand over field-collected asset data to a GIS, it is important to understand how to use RTK surveying and the tricks of data processing. This article explains the basics of RTK, how to survey field assets with attributes, and key points for accurately delivering the results to GIS. I hope this serves as a reference for improving the accuracy and efficiency of your routine surveying work.

What is RTK?

RTK stands for Real Time Kinematic, a real-time high-precision positioning technique using GNSS (satellite positioning systems). By continuously comparing observation data from a base station (reference point) and a rover (mobile receiver) via communications and applying error corrections, RTK can reduce positioning errors that are several meters (several ft) with regular GPS down to the order of a few centimeters (a few in). This is a major characteristic of RTK.

RTK technology is being applied across many fields—drone aerial surveying, as-built checking on construction sites, autonomous operation of agricultural machinery, and more—and is becoming a leading method in field surveying alongside conventional total station surveys. Coordinates obtained by RTK are usually expressed as geographic coordinates or plane rectangular coordinates based on global geodetic systems (WGS84 or Japan’s JGD2011).

GIS and Attribute Information of Field Assets

GIS (Geographic Information System) is a system for managing and visualizing various types of information on maps, and it is used in wide fields such as infrastructure management and urban planning. Data for field assets managed in a GIS (road signs, utility poles, sewer manholes, etc.) are linked not only to simple position coordinates but also to detailed attribute information such as names, types, and installation dates.

For example, when registering a single utility pole in a GIS, besides its latitude and longitude coordinates, you would attach information such as management number, type (power pole, communication pole, etc.), installation date, and owner. Rich attribute information allows easy analysis and maintenance management in GIS, such as extracting only specific equipment or searching for aging facilities. Conversely, if attributes are missing or incorrect, even carefully surveyed data may be useless in the field.

Therefore, when surveying in the field it is important to accurately record the required attribute items at the same time as the position. Traditionally, coordinates and equipment notes were sometimes recorded separately and reconciled later, but this approach tends to result in linkage errors or missing entries. Recently, mobile apps and devices that support RTK positioning have appeared, enabling direct input of attribute information on site for each survey point and saving them as integrated data. Using these methods can greatly streamline the workflow from field inspection to delivery.

Procedure for Surveying Field Assets with RTK

• Preparation before surveying: Before starting, prepare the necessary equipment and information. Ready an RTK-capable GNSS receiver (rover), a base station (or a subscription to a network RTK service), and a controller device for measurement (a tablet or smartphone for data collection). Also, confirm the reference coordinate system (e.g., plane rectangular coordinate system zone ○) and geodetic datum (e.g., JGD2011) for the survey area in advance and configure the equipment accordingly. If the client provides known points (reference points with known coordinates), having those coordinates is useful later for coordinate alignment (localization). Organize the attribute items to be recorded on site and prepare field survey forms or input templates as needed.

• Field surveying and data recording: Upon arrival at the site, set up the RTK environment. If deploying a base station, position it precisely and operate it; if using network RTK, connect the controller device to the correction service. Once the rover receives corrections, start surveying and confirm that the GNSS solution is Fix (fixed solution). For each asset, place the receiver at its location and record the positioning result. At that time, input attribute information such as equipment ID, name, and type on the dedicated device or app and link it to the point data. Take photos and notes as needed; these help later when reviewing the data. Proceed to record the positions and attributes for all targets at the site using this procedure.

• Data verification: After surveying is complete, verify the collected data on-site. Display the recorded points on the device’s map and check that they are plotted in the expected locations. Also confirm that all attribute information has been entered without omissions and that there are no typos or other defects. If possible, measure one known point or a recognizable landmark and verify that it matches its existing coordinates to validate overall accuracy. If any problems are found on site, re-measure or add notes as much as possible to avoid missing data.

• Data saving and export: Collected data are saved on the device. After surveying, export the data in a format that a GIS can read. Export methods depend on the equipment and app used, but typically you can generate files such as CSV or Shapefile that include coordinates and attribute information. When exporting, check the coordinate system and datum settings and, if necessary, convert to the coordinate system specified by the GIS. For example, if the delivery requirement is “plane rectangular coordinate system zone ○ coordinates,” select that coordinate system in the export settings when writing the data.

• Importing into GIS and delivery: Finally, import the exported data into GIS software and verify the contents. Check whether the loaded points are displayed in the correct positions on the map by overlaying them with existing drawings or aerial photographs. Also confirm that all attribute information is stored as expected. If coordinate misalignment is observed, specify the appropriate coordinate system in the GIS and reload, or use a transformation tool to correct it. If the data are fine, submit the complete set of files (e.g., the Shapefile .shp, .dbf, etc.) as the deliverable. It is helpful to include documentation describing the coordinate system used, surveying methods, survey dates, and so on so the recipient can confidently use the data.

Key Points for Accurate Delivery

• Unify coordinate systems: It is important to make the RTK-derived coordinate system consistent with the one used by the delivery recipient. Surveying can produce geographic or planar coordinates based on global geodetic systems, but if drawings or existing data use a local custom coordinate system, the numbers will not match as-is. Even within the same plane rectangular coordinate system, different zone numbers (regions) have different origins, which can cause large offsets between datasets. Perform localization (site calibration) using known points as needed to align RTK-acquired coordinates to the site’s coordinate system. It is desirable to secure three or more known points for localization. Measuring three points and computing correction parameters allows not only translation but also correction of rotation and scale differences, fitting the data more precisely to the site coordinate system.

• Check the geodetic datum: If datums differ, identical coordinate values can represent different actual positions. In Japan, global geodetic systems (JGD2000/2011) have been used since 2002, but older drawings or cadastral maps may use the old Tokyo datum. In such cases, use official conversion parameters or software to transform coordinates from the old datum to the new one. When overlaying old reference data with new survey results, always perform an appropriate datum transformation before integration.

• Vertical datum consistency: Pay attention to vertical reference standards as well. Heights obtained by RTK are ellipsoidal heights from GNSS and differ from orthometric heights (heights above mean sea level) used in common drawings. Convert ellipsoidal heights to orthometric heights by considering the local geoid height (geoid undulation) or correct height differences by measuring local bench marks with RTK. Confirm vertical consistency as needed and reflect it in the delivered data.

• Unify unit systems: Be careful about differences in units between surveying data and design data. Overlaying metric survey results on drawings labeled in feet will obviously cause misalignment, and there are cases where coordinate values exported from CAD in millimeters were combined with survey data recorded in meters, causing errors by a factor of 1000. Confirm that both parties use the same units before delivery in addition to matching coordinate systems.

• Attribute data consistency: Ensure attribute information is free of omissions and errors. Pay particular attention to uniqueness and variations in notation for equipment IDs and names. Use consistent codes or terms for values indicating the same type and verify that required fields are filled for all points. Exporting a list to a spreadsheet for visual inspection is effective. Incomplete attribute data prevent analysis and searching in GIS, reducing the value of the deliverable.

• Data quality and metadata: Perform an overall quality check before delivery. Compare a few sampled points with known positions or overlay them in GIS to verify positional accuracy and attribute content. Also attach metadata such as the coordinate system used, surveying methods, and survey dates. Providing these prerequisites helps the recipient correctly understand and confidently use the data.

Simple Surveying with LRTK

Recently, tools that make RTK positioning and coordinate alignment easier have appeared. For example, LRTK is a high-precision GNSS device used with smartphones that is effective for simple field surveying. By selecting the region’s coordinate system in a dedicated smartphone app, the positioning results can be converted and displayed in real time as X, Y, Z coordinates of that coordinate system (public coordinate system), allowing you to obtain coordinates in the same reference frame as the design drawings from the outset. The app also includes a function to register known points on site and perform one-touch coordinate correction (localization), completing coordinate alignment quickly without manual calculations. In one civil engineering site, setting localization with 2–3 reference points using LRTK resulted in all subsequent as-built measurements being recorded in the public coordinate system. As a result, the acquired coordinates could be directly reflected in electronic-delivery drawings without post-processing coordinate conversions, greatly improving efficiency.

By using LRTK in this way, anyone can easily achieve high-precision positioning and coordinate alignment without specialized knowledge. It reduces the burden on-site and offers high mobility, enabling a single person to walk large sites for surveying and inspection. LRTK is intuitive even for RTK beginners and is a powerful ally for experienced surveyors to shorten work times. Eliminating worries about coordinate mismatches, tools like LRTK are expected to attract growing attention as solutions that promote DX (digital transformation) at construction sites.

FAQ

Q1. What equipment and environment are needed to perform RTK surveying? A. To start RTK surveying you need a GNSS receiver (rover) capable of centimeter-level positioning (cm level accuracy; half-inch accuracy) and a base station that provides reference corrections. Traditionally, deploying your own base station was common, but now you can also use network RTK services that deliver corrections via cellular communications (public correction services using the Geospatial Information Authority of Japan’s continuous GNSS network or private VRS services, etc.). With such services, you do not need to set up a base station; having a rover and a communication device (smartphone, etc.) is sufficient to receive real-time corrections for high-precision positioning. In any case, a stable correction source (radio or internet) and a measurement environment with a clear view of the sky are essential for RTK surveying.

Q2. What level of accuracy can be obtained with RTK positioning? A. Generally, RTK provides horizontal positioning errors on the order of 2–3 cm (0.8–1.2 in) and vertical accuracy on the order of a few centimeters to several tens of centimeters (a few in to several tens of in). However, this varies depending on satellite reception conditions, distance from the reference station, and the environment. Under ideal conditions, errors can be within the 1 cm range (cm level accuracy; half-inch accuracy), but accuracy degrades near tree cover or tall buildings due to multipath and signal blockage. RTK accuracy is markedly better than typical smartphone GPS (about 5–10 m (16.4–32.8 ft) error) and can rival conventional total station surveys.

Q3. How do I import measured data into GIS? A. Transfer RTK-measured point data and attribute information to a computer and then import them into GIS software. In many cases, surveying equipment software or apps can export data as Shapefile or CSV, which you then load into GIS. If you match the coordinate system (projection) settings in the GIS, the recorded positions will be plotted in the correct locations on the map. If attributes are included in the import, you can click points in the GIS to view details, filter, or display them with different colors.

Q4. Any tips for recording attribute information in the field? A. First, prepare a list of items to record in advance to avoid omissions on site. Because field work can be rushed, follow a predetermined format (checklist or tablet input form) and fill in each item one by one. Use input methods that reduce mistakes, such as selection lists for categories or conditions. Also, take photos for each measured point and link them to the point IDs so you can understand the situation when reviewing data later. The key is to complete as much information as possible on site so you don’t have to wonder later “what was this point?”

Q5. Any easier way to start RTK surveying? A. User-friendly RTK surveying tools have recently appeared. One example is LRTK, introduced in this article. LRTK is a smartphone-based high-precision GNSS solution that lets anyone easily perform centimeter-level positioning (cm level accuracy; half-inch accuracy) without worrying about complex coordinate transformations. Simply select the reference coordinate system in the dedicated app to obtain accurate coordinates in real time, making it ideal for those new to RTK. Compared to traditional surveying equipment, it is compact and affordable, making it a strong option for those who want to quickly adopt high-precision positioning. LRTK is also compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction (ICT construction) initiative and draws attention as a solution supporting digital transformation on construction sites.

Q6. Do I need to perform localization for every project? A. Basically, if the coordinate system differs by site or project, it is recommended to perform localization (coordinate alignment using known points) each time. If the same public coordinate system is used across sites, you may not need to do it each time, but it is good practice to confirm at least one known point before starting surveying to check for any offsets compared to the drawing coordinates. If discrepancies are found, immediately perform localization using multiple points to correct them. Localization takes an extra step, but it serves as insurance against major rework caused by positional offsets, ultimately improving efficiency and quality. Performing localization—though a bit of effort—can prevent future mistakes.