In practical fields such as construction and surveying, the accuracy of position information greatly affects the quality and efficiency of work. Standalone GPS positioning typically has errors of several meters, but by using high-precision GNSS positioning technologies, those errors can be reduced to the order of several centimeters.

Representative high-precision GNSS positioning methods include RTK (Real Time Kinematic), DGPS (Differential GPS), and PPP (Precise Point Positioning). Each has different positioning mechanisms and characteristics, so it is important to choose according to the intended use.

This article focuses on the differences between RTK and DGPS, clearly comparing their mechanisms, accuracy differences, and recommended uses. It also introduces simple surveying using the latest technology LRTK and answers RTK-related questions for beginners and practitioners alike.

Table of Contents

• What is RTK?

• What is DGPS?

• Differences between RTK and DGPS

• Quick recommendation table by use case for RTK and DGPS

• Simple surveying using LRTK

• FAQ

What is RTK?

RTK (Real Time Kinematic) is a technology that corrects GNSS positioning errors in real time to achieve centimeter-level accuracy. The basic principle uses at least two GNSS receivers: one set up as a base station at a known coordinate, and another as a rover mounted on the object to be positioned. The base station compares its accurate coordinate with observations from GNSS satellites to calculate error components and sends that correction information to the rover via radio communication or the Internet (such as NTRIP). The rover applies the received correction data to its own positioning, canceling error factors included in satellite positioning and obtaining a highly accurate current position in real time.

RTK dramatically improves the accuracy of standalone GNSS positioning, which is normally on the order of several meters, down to the order of centimeters. In practice, about 2～3 cm (0.8～1.2 in) in horizontal position and about 3～4 cm (1.2～1.6 in) in height can be obtained, which is sufficient for civil engineering surveying and automatic control of construction machinery. The major advantage of RTK is that high-precision positioning results are obtained immediately; in surveying sites, it is widely used by setting up a base station and carrying a rover to observe point coordinates one after another, or mounting a rover on construction machinery to continuously correct the work position, taking advantage of real-time positioning.

RTK is a form of relative positioning (differential positioning), and the closer the base station and rover are, the more common error factors they share, resulting in stable high accuracy. Generally, base stations and rovers operate within a range of several km～several tens of km and need to receive correction information continuously via a communication line, but once the system is configured, positioning results continue to be updated in real time. Recently, networked RTK services using national geodetic stations (VRS method) provided via the Internet by agencies such as the Geospatial Information Authority have become widespread. Such infrastructure development has increased scenarios where high-precision positioning can be used without installing a private base station, and RTK has become the de facto standard technology for high-precision GNSS positioning in construction and surveying.

What is DGPS?

DGPS (Differential GPS) is also a method that corrects GNSS positioning errors using a base station and a rover, similar to RTK. However, while RTK uses the phase information of satellite signals, DGPS mainly uses differential corrections of the code (pseudorange). The basic configuration is similar to RTK: a stationary base station computes the difference between its self-determined GPS coordinates and the accurate known coordinate, and sends that differential data to the rover. The rover uses the received differential information to correct its own positioning values and achieve higher accuracy than standalone positioning. The general category of real-time differential GNSS methods is called DGPS (in a narrow sense it may refer specifically to code-differential GPS).

The accuracy improvement by DGPS is generally on the order of several tens of centimeters in horizontal position. For example, within several km of a base station, errors can be kept under 1 m (sub-meter class). However, because it does not perform integer ambiguity resolution of carrier-phase cycles like RTK and relies on simple code-based differential corrections, it does not reach centimeter-level accuracy. Instead, it has advantages such as lower initial setup hurdles, compatibility with inexpensive single-frequency GNSS receivers, and relatively low communication data volume. A representative form of DGPS is satellite-based augmentation systems (SBAS). Japan’s MSAS and the U.S. WAAS broadcast wide-area error information derived from multiple ground reference stations via geostationary satellites; compatible receivers can receive those correction signals and improve standalone positioning accuracy to about 1 m (3.3 ft) horizontally and about 1.5 m (4.9 ft) vertically. Thus, DGPS is characterized by ease of applying corrections over wide areas even though its accuracy is inferior to RTK. In Japan, the Japan Coast Guard has long provided DGPS correction information to coastal areas nationwide via medium-wave radio beacons, and by using dedicated receivers, positioning accuracy of about 1–2 m can be achieved near harbors. Providing wide-area differential corrections through dedicated infrastructure is another advantage of DGPS.

In a broad sense, RTK can also be considered a type of differential GNSS (DGPS). While conventional DGPS remained limited to code-based differentials, RTK achieves dramatic increases in accuracy by incorporating advanced processing such as double-differencing of carrier-phase and ambiguity resolution. As a result, DGPS is sub-meter class in accuracy, whereas RTK provides centimeter-level accuracy and has become mainstream in surveying and construction sites that require high precision.

Differences between RTK and DGPS

The main differences between RTK and DGPS can be summarized as follows.

• Positioning accuracy: RTK achieves centimeter-level accuracy in both horizontal and vertical directions. DGPS typically achieves under 1 m (several tens of cm) accuracy, so RTK is orders of magnitude more accurate.

• Correction method: RTK uses GNSS carrier-phase and removes errors via integer ambiguity resolution and double-differencing. DGPS mainly uses single-difference corrections for satellite signal code (pseudorange), which is a simpler method.

• Required equipment: RTK requires two GNSS receivers (base and rover), and higher performance equipment such as multi-frequency support is desirable to improve accuracy (or you can use public base station services). DGPS can be used with a single receiver (only to receive correction information), and single-frequency inexpensive devices or commercial GPS units can support differential corrections.

• Communication environment: RTK requires a communication environment capable of continuously receiving real-time corrections via radio or the Internet. DGPS also generally requires reception of correction information, but systems like SBAS broadcast corrections from satellites unilaterally, making communication setup easier.

• Applicable range: RTK accuracy degrades if the distance to the base station is too large, so it is typically used within several tens of km. DGPS (SBAS) can apply the same corrections over wide areas and has fewer geographic constraints.

• Cost and operation: Traditionally, RTK required significant initial investment for dedicated equipment and base station installation and required expert knowledge to operate. DGPS was relatively low-cost and easy to introduce. However, in recent years RTK equipment has become smaller and cheaper, and easy-to-use solutions such as LRTK have emerged, greatly lowering the barrier to RTK adoption.

Note: There is also PPP (Precise Point Positioning), which can achieve centimeter-level accuracy without a base station using a single receiver. However, to achieve high accuracy in real time, PPP requires a convergence time of several minutes to tens of minutes, making it unsuitable for on-site work that requires immediacy (it is effective where measurement time can be long).

Quick recommendation table by use case for RTK and DGPS

So in which situations should you use RTK, and in what situations is DGPS sufficient? Below are recommendations by use case.

RTK is recommended for:

• Precision surveying at civil engineering and construction sites (boundary and control point surveys, as-built management, setting out batter boards, etc., where centimeter-level precision is required)

• Machine guidance/machine control for construction equipment (real-time, high-precision correction of heavy machinery position during operations)

• Precision agriculture (e.g., to keep row alignment within a few cm for autonomous tractors during seeding or fertilization)

• Drone photogrammetry (applying RTK corrections to aerial imagery to create high-precision terrain maps while minimizing ground control points)

DGPS is sufficient for:

• General car navigation or smartphone map apps and other location services where meter-level errors are acceptable

• Coastal vessel navigation assistance and aviation navigation augmentation (SBAS improves positioning accuracy to assist safe navigation and landings)

• Simple surveying or preliminary investigations for GIS (recording feature positions or environmental surveys where ~1 m accuracy is sufficient, using inexpensive GPS receivers with differential corrections)

Simple surveying using LRTK

In recent years, RTK positioning has evolved further. Where conventional RTK surveying required expensive, specialized, stationary GNSS receivers and large antennas, the latest LRTK (el-arr-tee-kay) technology has made RTK dramatically smaller and simpler, making it increasingly easy for anyone to use. LRTK is a solution consisting of an ultra-compact RTK-GNSS receiver that can be attached to a smartphone or tablet, a dedicated app, and cloud services. For example, the product "LRTK Phone" turns an iPhone or iPad into a centimeter-class surveying instrument simply by attaching a slim RTK device. The pocket-sized device, weighing only just over 100 grams, houses a battery and antenna and is easy to carry to the field for immediate positioning when needed.

In practice, using a dedicated monopod adapter allows a single person to perform simple single-point positioning easily. Since the height offset from the tip of the pole is automatically calculated in the app, the complicated corrections required by conventional surveying instruments are unnecessary. Because anyone can perform accurate positioning with simple operations, tasks that were previously left to professional surveyors can be handled in-house by company staff.

LRTK’s strengths are not only in its small size and simplicity but also in data utilization via cloud services and low-cost introduction. Positioning data and point cloud data obtained in the dedicated app can be saved and shared to the cloud in real time, allowing coordinates measured in the field to be checked immediately at the office. Advanced digital tools such as AR functions enable position-setting work by overlaying design models onto live site images. Where RTK equipment once cost several million yen, LRTK offers an order-of-magnitude cheaper option, making it accessible even to small and medium construction and surveying firms—a kind of "democratization" of RTK positioning. With about a five-minute simple explanation, anyone can master its use; no special surveying knowledge is required to perform accurate positioning alone.

Consider introducing LRTK to make high-precision surveying more accessible and improve field productivity. For more details, please also see the [LRTK official site](https://www.lrtk.lefixea.com).

FAQ

Q. How different are the positioning accuracies of RTK and DGPS? A. RTK provides about 2～3 cm (0.8～1.2 in) horizontally and about 3～4 cm (1.2～1.6 in) vertically. DGPS (Differential GPS) typically achieves around 1 m (3.3 ft) accuracy and in good conditions can reach several tens of centimeters. Therefore, RTK is chosen when centimeter-level precision is required, while DGPS is suitable when sub-meter accuracy is sufficient.

Q. What is needed to use RTK positioning? A. Basically, a high-precision GNSS receiver (rover), a base station (or a correction service acting as a substitute) that provides error correction information, and a communication method to connect them are necessary. If you run your own RTK, you set up a GNSS base station at a known point and connect to the rover via radio communication. A simple method is to subscribe to a networked base station service (such as VRS via Ntrip) provided by an authority like the Geospatial Information Authority, and connect the rover receiver (for example an LRTK device) to that service via a smartphone to receive corrections over the Internet. In any case, obtaining centimeter-level accuracy requires a high-quality receiver and an environment for continuous reception of correction data.

Q. Is DGPS no longer used? A. No, DGPS is still widely used depending on the application. Where RTK-level accuracy is unnecessary, DGPS or SBAS corrections are sufficient. For example, vessel navigation uses DGPS radio beacons from coastal stations or SBAS via satellites to achieve meter-level accuracy improvements, and aviation uses SBAS to enhance GPS accuracy for safe navigation and landing. Simple surveying devices for GIS commonly use sub-meter positioning via SBAS, and DGPS remains useful for applications where errors of several tens of centimeters are acceptable.

Q. Can centimeter-level positioning be achieved without a base station? A. There is a method called PPP (Precise Point Positioning) that can achieve centimeter-level accuracy with a single receiver. PPP uses precise corrections for satellite orbit and clock errors derived from global GNSS observation networks to enable high-precision positioning with one receiver. However, real-time convergence to centimeter accuracy requires several minutes to tens of minutes of initialization time, so it is unsuitable for tasks requiring immediate results (high-accuracy results can be obtained by long static observation beforehand or by post-processing). Regional fast-PPP services such as the CLAS signal from Japan’s QZSS have recently appeared, but for general field work where communications are available, RTK that provides immediate high accuracy is still preferable.

Q. What is LRTK? A. LRTK is an RTK-GNSS positioning system that can be easily used with a smartphone. It consists of a small GNSS receiver device that attaches to a smartphone or tablet and a dedicated app, enabling centimeter-level positioning for anyone. Compared with conventional stationary RTK equipment, it is overwhelmingly inexpensive, easy to carry and set up, and allows non-specialist users to perform high-precision positioning in the field. By utilizing LRTK, firms can internalize previously outsourced surveying, acquire high-precision data more frequently, and accelerate on-site digital transformation (DX).

Q. What is the difference between GNSS and GPS? A. GPS is the name of the U.S. satellite positioning system, but other countries and regions operate their own satellite positioning networks, such as Russia’s GLONASS, Europe’s Galileo, and Japan’s QZSS. GNSS (Global Navigation Satellite System) is a collective term for these multiple satellite positioning systems. In high-precision positioning like RTK and DGPS, it is common to use multiple GNSS to increase the number of visible satellites and improve positioning stability and accuracy.

Q. Does RTK positioning take time? A. In RTK, it generally takes from a few seconds to a few tens of seconds after powering on the receiver to obtain a high-precision solution called a “fixed solution.” Depending on satellite visibility and surrounding conditions, it may take up to about a minute initially, but it does not require the long waiting times associated with DGPS or PPP. Once a fixed solution is obtained, centimeter-precision positions are updated in real time as long as correction information continues to be received. If the fixed solution is lost due to satellite signal loss, recovery typically occurs again in a few seconds.

Above is an explanation of the differences between RTK and DGPS, how to choose between them, and the latest solution LRTK. Choose the positioning technology that fits your needs and use it to improve on-site operational efficiency.