How to Prevent Unit and Scale Mistakes in RTK Outputs

Table of Contents

• Introduction

• The Importance of RTK Positioning and Units/Scale

• Differences Between the World Geodetic System (WGS84) and Local Reference Frames

• 1. Reference Station Coordinate Setting Errors – Large Position Offsets

• 2. Forgetting to Convert to the Local Geodetic System – Risk of Data Mismatch

• 3. Confusing Feet and Meters – Abnormal Scale Errors

• Simple Surveying with LRTK

• For more details on LRTK, see the links below.

• FAQ

Introduction

RTK (Real Time Kinematic) surveying is a method that corrects GNSS satellite positioning errors in real time to achieve centimeter-level precision. Standalone GPS positioning can yield errors of several meters, but with RTK you can reduce errors on site to about 1–2 cm (0.4–0.8 in), so it is widely used in civil engineering and land surveying. However, no matter how high the positioning accuracy of RTK is, if you misconfigure the units or the coordinate reference frame, the measurement results can be significantly off. In practice, discrepancies due to differences in the reference geodetic datum or scale errors caused by confusing length units become issues on survey sites. This article focuses on “how to prevent unit and scale mistakes in RTK outputs,” and explains common failure cases and countermeasures in detail. Whether you are working on international projects overseas or conducting surveys domestically and are unsure about coordinate systems or units, please use this as a reference.

The Importance of RTK Positioning and Units/Scale

First, let’s review the basics of RTK positioning. RTK, short for Real Time Kinematic, is a technology that exchanges GNSS observation data between a reference station installed at a known control point and a rover at the point to be measured, and by applying real-time corrections obtains high-precision coordinates. The reference station is provided with accurate coordinates in advance, and the rover applies correction information sent from the reference station to correct its own positioning results. With this mechanism, GNSS standalone positioning results that would normally be off by several meters can be reduced to within a few centimeters using RTK.

That said, the coordinates obtained by RTK are always based on some reference coordinate system (geodetic datum). A geodetic datum is a framework that defines positions on the Earth, and due to differences in the underlying ellipsoid or origin, the numerical latitude, longitude, or coordinates for the same point can differ. Survey data also involve units of distance. If a country or region uses non-metric systems such as traditional local units or the yard–pound system, confusing the unit system can cause significant scale errors. In other words, ensuring accuracy in RTK surveying requires correctly understanding and managing the reference coordinate system and unit system.

Differences Between the World Geodetic System (WGS84) and Local Reference Frames

The standard coordinate reference used internally by GNSS equipment is the World Geodetic System (WGS84). Latitude, longitude, and height output by GNSS receivers are generally given in WGS84. However, many countries have local geodetic systems optimized historically for their territory, and official surveying results and maps are often produced using those national datums. For example, the United States uses NAD83 (North American Datum 1983) as its continental reference datum, which differs from WGS84 in the defining ellipsoid and origin. NAD83 and WGS84 were almost identical when established, but since WGS84 has been continuously updated using the Earth’s center of mass as a reference, today there is a difference of about 1–2 m (3.3–6.6 ft) between the two in the US mainland. Thus, overlaying RTK positioning results in WGS84 directly onto drawings or maps based on NAD83 in the US can cause positional mismatches of roughly 1–2 m (3.3–6.6 ft) (differences vary by region and epoch). In surveys that require millimeter-level accuracy, a 1–2 m discrepancy can be critical.

The differences in datums also affect vertical references. Heights obtained directly from GNSS are ellipsoidal heights measured from the reference ellipsoid, while many countries use orthometric heights based on mean sea level (geoid-based heights). For example, comparing the US official vertical datum (NAVD88) with WGS84 ellipsoidal heights shows differences of up to several tens of meters depending on location. Therefore, when handling height information in RTK surveying, converting and correcting to the local vertical datum (geoid) is indispensable.

As described above, if the country or region differs, the reference coordinate systems differ; applying RTK coordinate data acquired in WGS84 directly to local maps or design coordinate systems can produce position deviations from several meters to, in some cases, tens of meters. Also, since distance units are not standardized internationally, confusing meters and feet can produce scale differences of about 3.3 times. From the next sections, we will look at representative error cases caused by these datum and unit differences and specific prevention measures.

1. Reference Station Coordinate Setting Errors - Large Position Offsets

Failure example: In RTK surveying, the basic procedure is to first set accurate known coordinates in the reference station (base station). However, on overseas sites this reference station coordinate setting error tends to occur frequently. For example, a common mistake is entering coordinate values for the reference station without considering the local datum, simply using the coordinates that were used in Japan. If you assume that control point coordinates used in Japan (e.g., JGD2000/JGD2011) are the local reference in the US and enter them as such, the measurement points will shift by the difference between the actual local datum (WGS84 or NAD83) and the coordinates you entered. In some cases all measured points may be offset by tens of meters, and because measurements on site may appear to succeed, the mistake can be hard to notice. Deliverables later will not match the existing maps or drawings, causing major rework. Mistakes such as digit errors when entering coordinates (e.g., one digit wrong in degrees/minutes/seconds) or confusing latitude/longitude with plane rectangular coordinates when entering values can also cause large position offsets. Especially in unfamiliar overseas work, extreme care is required when setting reference station coordinates.

Countermeasures:

• Use official local control points: When installing a reference station, obtain coordinate values for official known points in the area (control points used in designs or triangulation points) and set those coordinates in the reference station whenever possible. Using local official datum coordinates from the start will prevent overall shifts due to differences in datum. If you must use an unknown point as a reference station, measure multiple surrounding known points so you can later convert to the local coordinate system for checks.

• Double-check coordinate entry: When entering known coordinates into the reference station, always double-check the datum and coordinate values. Verify the number of digits, signs (east/west sign conventions), and which coordinate system is being used (latitude/longitude or plane rectangular coordinates and which datum) against a checklist, and if uncertain have another operator cross-check. In the US, manually entering longitude without a negative sign for west (e.g., entering 100°E instead of 100°W) is a common mistake. Also be mindful of omitted zone numbers and other easily overlooked settings; enforce careful double-checking at input.

• Validate with test measurements: After setting the reference station, immediately test-measure nearby known points with the rover to verify you obtain expected coordinates. Confirm the obtained values match maps or control point records. If you find offsets of several meters or more at this early stage, you can promptly review and correct settings.

• Establish standard procedures: Prepare internal standard procedures and checklists that include the above precautions so that reference station setup achieves consistent quality regardless of operator. For overseas projects in particular, coordinate setting errors can lead to fatal losses; build organizational measures to prevent human error.

2. Forgetting to Convert to the Local Geodetic System - Risk of Data Mismatch

Failure example: RTK positioning results obtained from GNSS receivers are by default WGS84 coordinates, but there are many cases where data are delivered without converting them to the local official geodetic system. Because each country has different official horizontal and vertical datums, failing to perform conversions can lead to the serious problem that surveying results do not match local maps or design coordinate systems. For example, in a US project, point-cloud data obtained by RTK were submitted in WGS84 latitude/longitude and not converted to NAD83 or the state plane coordinate system, causing the data to be offset by tens of meters on the map and resulting in major rework. Conversion errors can also arise from differences in how east/west longitude is represented, or from differences in projection zones (e.g., UTM zone numbers). In the US, many states use state plane coordinate systems and surveying feet as units, and “omitting coordinate conversion” or unit conversion errors are common causes of data inconsistency.

Countermeasures:

• Confirm the official local coordinate system in advance: At project kickoff, investigate the horizontal and vertical datums that should be used in that country or region and establish a unified rule for the team. Identify the datum adopted by each country/state (e.g., NAD83 for the US, ETRS89 for Europe), coordinate system types (e.g., which UTM zone, state plane zone number), and units (feet or meters), and ensure the project consistently uses the same datum and unit system.

• Configure equipment to output local coordinates: Check GNSS receivers and surveying software settings so that, where possible, data are output in the local datum/coordinate system from the start. For example, when using network RTK services overseas, confirm whether the service’s reference frame matches the project datum and change the receiver’s output datum if necessary. Recording in the local coordinate system from the beginning reduces the risk of conversion errors in later stages.

• Use official tools for accurate conversion: If you need to convert WGS84 data to a local system after measurement, use official transformation parameters or software provided by national geodetic authorities to perform transformations with guaranteed accuracy. In the US, use transformation tools from agencies like the USGS or NGS; in Japan, use transformation parameters from the Geospatial Information Authority of Japan. Avoid manual calculations or rule-of-thumb conversions that can introduce errors or human mistakes.

• Verify conversion results: After transforming coordinates, always verify results against local known points or official maps. For example, plot transformed data on local topographic maps to ensure control points and landmarks align. Detecting discrepancies here allows you to correct them before delivery. Although it may seem tedious, this verification prevents the critical error of delivering data that do not match maps.

3. Confusing Feet and Meters – Abnormal Scale Errors

Failure example: Alongside datum differences, the length unit differences—especially in the US—require attention. Surveying and design drawings in the US commonly use the yard–pound system, i.e., units like feet and yards rather than the metric system. Therefore, mistakes in confusing whether a distance or coordinate value is in feet or meters are common. For example, if a drawing or control point table shows the number “1000” and that value is actually in feet but you mistakenly interpret it as meters when setting a reference station or in software, you will create a scale error of about 3.28 times. Since 1000 feet is about 304.8 m (1,000 ft), interpreting it as 1000 m would be like treating a point actually 304.8 m away as 1000 m away, causing major mismatches. Conversely, if you measure in meters but the recipient assumes feet, your drawing will be off by more than three times. Such unit conversion mistakes are basic yet surprisingly frequent in international projects. Note also that there are two different definitions of the foot—international foot and US survey foot—and confusing them can lead to small ppm-level discrepancies (1 ft = 0.3048 m or 1 ft = 1200/3937 m). Some states historically used the survey foot; mixing unit definitions can accumulate slight offsets (note: the US has been moving to eliminate the survey foot in favor of the international foot since 2023).

Countermeasures:

• Clearly specify and confirm unit systems: When handling survey data or drawings, always confirm whether values are in feet or meters. If units are not noted on the issued drawings or control point tables, contact the client early to clarify, and do not proceed with work while the units remain ambiguous. Also, when delivering final coordinates or distances, annotate units explicitly to avoid misunderstandings.

• Check software unit settings: Verify the unit settings in surveying instruments, CAD software, and other tools in advance, and set them to match the units used locally. For example, US-oriented software may default to feet, while equipment brought from Japan may always output meters. Switch settings as needed before measurements begin to avoid input/output unit confusion.

• Ensure accurate conversions: When converting units, use precise conversion factors. The conversion between feet and meters is defined as 1 foot = 0.3048 m. When performing calculations in spreadsheets or other tools, maintain sufficient decimal precision to avoid rounding errors. Use surveying software’s automatic conversion functions where possible. Also, check whether a state uses the survey foot or the international foot in advance to avoid subtle discrepancies.

• Standardize units within the team: Unify the units used across the project and make them known to all members. For example, document rules like “horizontal distances delivered in international feet, heights converted to meters” and apply them consistently. When working together with local staff, align unit handling in advance to overcome language barriers and ensure shared understanding.

So far we have reviewed representative mistakes and countermeasures caused by differences in datums and unit systems. RTK surveying itself is very high precision, but it fundamentally requires aligning the reference coordinate system correctly and reliably performing data transformations and unit conversions. Neglecting these aspects can render centimeter-level accuracy meaningless and produce misaligned results. Conversely, with careful preparation and verification, you can prevent measurement quality issues and data inconsistencies in any site, including overseas locations, and successfully carry out RTK surveys.

In recent years, technological advances have produced solutions that greatly reduce these cumbersome steps and the risk of human error. One such solution is LRTK, which combines a smartphone with a small high-precision GNSS receiver to enable anyone to perform centimeter-precision surveying easily.

Simple Surveying with LRTK

LRTK is an all-in-one surveying system that lets you attach a dedicated ultra-compact RTK-GNSS receiver to a smartphone and perform high-precision positioning with a single tap using a dedicated app. A key feature is that you can obtain accurate global coordinates (WGS84) on site immediately without complex base-station preparation or specialized coordinate settings. Collected positioning data are automatically saved to the cloud and can be easily shared with the office team in real time. LRTK’s high-performance receivers support multi-GNSS and multi-frequency, so you can expect stable positioning aided by SBAS, Japan’s QZSS “Michibiki” centimeter-class augmentation signals (CLAS), and stable performance even in mountainous or overseas areas with limited network connectivity. The system is designed to be intuitive with no complicated device operations, enabling one person to use it immediately; when used by multiple people, advanced technical training is not required, substantially reducing training burdens for local staff.

As a smartphone × compact GNSS “simple surveying device,” LRTK is attracting attention as a new option that smartly resolves common challenges when introducing RTK overseas (datum differences, limited communication infrastructure, human errors, etc.). Even if you feel that operating RTK overseas is difficult and worrisome, using modern solutions like LRTK allows you to perform RTK surveying more simply and reliably. It is a tool that leverages technology to update on-site surveying workflows to the next level. The LRTK series delivers high-precision GNSS positioning in construction, civil engineering, and surveying, dramatically improving measurement accuracy and work efficiency on site. For example, it supports the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative and strongly supports DX (digital transformation) in the construction industry.

For more details on LRTK, see the links below.

• [What is LRTK｜LRTK Official Site](https://www.lrtk.lefixea.com/)

• [LRTK Series｜Device List Page](https://www.lrtk.lefixea.com/lrtk-series)

For product inquiries, estimates, or implementation consultations, please feel free to contact us via the [inquiry form](https://www.lrtk.lefixea.com/contactlrtk). Use the latest LRTK to take your field operations to the next stage.

FAQ

Q1. How much do WGS84 and NAD83 datums differ? A. Both WGS84 and NAD83 are global coordinate datums, but at present there is about a 1–2 m (3.3–6.6 ft) difference in the US mainland. NAD83 is a datum fixed to the North American plate established in the 1980s, whereas WGS84 has been continuously revised using the Earth’s center of mass as a reference. Depending on the region, WGS84 coordinates are said to be offset roughly 1–2 m toward the northeast relative to NAD83 (differences vary by latitude/longitude definitions and realization epochs). In high-precision surveying this 1–2 m difference cannot be ignored. Therefore, US surveying results are generally unified to NAD83, and GNSS coordinates obtained in WGS84 should always be converted to NAD83. Note that a new US reference frame (NATRF2022) is planned to be introduced in the late 2020s to provide further high-precision unification.

Q2. Why do I need to check the datum in RTK surveying? A. RTK surveying itself uses relative positioning to achieve high precision, but the resulting coordinates are always based on a particular datum. If you carry out measurements in a coordinate datum different from the project’s adopted datum, even centimeter-level observation precision will include the datum offset (meter-level errors) in the results. For example, even point clouds measured to 1 cm precision by RTK could be displaced by several meters overall if the datums differ. This is not a measurement precision issue but a “datum error,” and once the data are offset you cannot restore correct positions without post-processing corrections. Therefore, when performing RTK surveying, always confirm before starting that the datum set in the reference station and the output datum for deliverables match the project’s standard. It is also important to check whether GNSS-derived heights are consistent with the local vertical datum (geoid). In short, unless you align “which datum you measured in,” RTK’s high precision will not be realized and practical data inconsistencies will occur.

Q3. Do I need to pay attention to length units (feet/meters) when surveying overseas? A. Yes, confirming the unit system is critical. In the US, distances and coordinates are commonly expressed in feet, yards, and other imperial units rather than the metric system used in Japan. If a drawing or control point data are in feet but you mistakenly treat them as meters, you will misplace positions by roughly 3.3 times (for example, confusing 100 feet for 100 meters leads to about a 70% positional error). Conversely, if you measure in meters and the recipient assumes feet, discrepancies of more than three times can occur. Unit confusion can be hard to detect later and difficult to correct, so always confirm units in advance and standardize them within the team. Also, although there are two definitions of the foot—international foot and survey foot—most cases are now standardized to 1 ft = 0.3048 m (the international foot), and the US has been moving to retire the survey foot since 2023. In any case, unify units among stakeholders and set software input/output settings correctly to avoid mistakes.

Q4. What kind of product is LRTK? A. LRTK is an ultra-compact RTK device that turns a smartphone into a high-precision surveying instrument. It consists of a small GNSS receiver attachable to a smartphone and a dedicated app, enabling real-time centimeter-level positioning on site. Traditionally, RTK surveying required large dedicated equipment and base station installation, but LRTK removes these hurdles and lets you complete tasks with just a smartphone. For example, attaching an LRTK receiver to a smartphone and operating the app enables high-precision GNSS positioning, 3D scanning, and AR-based position checks all in one. The receiver supports multi-GNSS and multi-band positioning and performs well with signals such as Japan’s Michibiki augmentation and standard network RTK. In short, LRTK is a next-generation tool that “makes your smartphone a high-precision surveying instrument,” offering exceptional portability and responsiveness to revolutionize on-site surveying workflows.

Q5. Can LRTK solve datum and unit mistakes? A. Using LRTK can greatly reduce human errors in reference station setup and positioning settings. LRTK fundamentally acquires accurate absolute coordinates in the WGS84 system, so it eliminates worries about entire datasets shifting because of incorrect base station coordinate input. That said, depending on project needs you will still convert acquired data into local coordinate systems; LRTK’s cloud and app can provide coordinate transformation and output settings. In other words, LRTK does not automatically correct for all datum differences, but because it makes it easy for anyone to obtain correct absolute coordinates, it helps ensure downstream conversion processes are performed correctly. Traditional surveying workflows relied heavily on manual steps from base station setup to coordinate conversion, creating many opportunities for mistakes, but LRTK simplifies these processes and thus minimizes the risk of datum-related failures. As software continues to evolve, features such as one-touch conversion to various national coordinate systems are expected to become more robust. In any case, leveraging LRTK will significantly reduce the overall effort and risk in surveying, including bridging datum gaps.