What are the differences between RTK surveying and GPS surveying? Comparing accuracy, cost, and applications from a field perspective

Table of Contents

• Basic mechanisms of GPS surveying and RTK surveying

• Differences in accuracy: standard GPS vs RTK surveying

• Cost comparison: initial costs and operating costs

• Differences in practical applications

• Measurement time and work efficiency

• Differences in impact due to environmental conditions

• Utilization of control point networks and measurement areas

• Technological advances and use of NTRIP streaming

• Examples of operations requiring measurement accuracy

• Future surveying technologies and the need for high-precision positioning information

• Devices that enable high-precision positioning with smartphones

• Summary

You often hear the terms "RTK" and "GPS" on surveying and construction sites. Both are satellite-based positioning technologies, but in practical fieldwork they operate at completely different levels of accuracy and their applications are correspondingly limited. This article clearly explains the differences between RTK surveying and GPS surveying from three perspectives—accuracy, cost, and applications—to provide the knowledge you need on site.

Basic Principles of GPS and RTK Surveying

GPS surveying is a surveying technique that receives radio signals from multiple satellites and calculates position information by using the differences in their arrival times. It was commercialized in the United States in the 1980s and is now a standard feature in car navigation systems and smartphones. Because it only requires receiving signals transmitted from satellites overhead, it is relatively simple and requires little additional facility investment.

On the other hand, RTK surveying, which stands for "Real-Time Kinematic," is a technique that, while based on GPS technology, dramatically increases accuracy by receiving correction signals from reference points installed on the ground. Signals from distant satellites always contain errors. By measuring those errors at the reference points and transmitting correction data in real time, centimeter-level precision (half-inch accuracy) becomes possible.

Differences in Accuracy: Standard GPS vs RTK Surveying

The typical accuracy of standard GPS surveying is generally a few meters (approximately 3–10 m (9.8–32.8 ft)). Smartphone GPS functions have similar accuracy, so that may make it easier to imagine. This accuracy can vary significantly between urban and suburban areas. In environments with many buildings and trees, signal reflections increase and accuracy may degrade further.

By contrast, RTK surveying can achieve centimeter-level (cm) accuracy, and even millimeter-level (mm) accuracy with higher-precision systems. In typical RTK surveying systems, horizontal errors can be kept to 2–5 centimeters (0.8–2.0 in) or less. This difference is dramatic in the field. In land boundary surveys and precise elevation measurements for construction sites, errors of several meters (several ft) can have a major impact on construction.

The reason for the high accuracy is that correction signals from the reference point are constantly transmitted in real time. The reference point detects error factors contained in the signals from the satellites (ionospheric delays, atmospheric effects, etc.) and wirelessly sends that information to the receiver. By receiving this correction information, the receiver can calculate a vastly more accurate position.

Cost Comparison: Initial Implementation Costs and Operating Costs

The biggest advantage of GPS surveying is cost. Basic position measurements are possible even with consumer-grade receivers such as smartphones, and professional GPS receivers can be deployed relatively inexpensively. Maintenance costs are also low, and no additional contracts or facilities are required. Since it only needs to receive signals from satellites, running costs are almost nonexistent.

Implementation costs for RTK surveying can vary significantly. A receiver capable of receiving multiple satellite signals simultaneously is required, and equipment prices increase as system precision improves. Even more important is the operation of reference stations. You need to establish reference stations in the area to be surveyed and provide the facilities and networks to transmit correction signals from those reference stations.

There are two main approaches to establishing reference points. One is the approach in which a company operates its reference points in-house; this requires a higher initial investment, but is economically advantageous in the long term for companies that carry out measurement work frequently. The other is the approach of using publicly available reference point networks. In many regions, public agencies maintain reference point networks, and by utilizing them the upfront/implementation costs can be reduced.

Differences in Practical Applications

GPS surveying is suitable for coarse position awareness when high accuracy is not required. For example, measuring the area of vast forests or roughly confirming the location of land. In disaster management, it is also used for confirming evacuation shelter locations and creating hazard maps, with an allowable error on the order of several meters (a few ft). It also provides sufficient accuracy for tracking positions while moving and for determining locations in emergencies.

RTK surveying is used for applications where high precision is essential. It is employed in tasks where accuracy directly affects the quality of the deliverables, such as batter board setting (driving reference stakes) on construction sites, cut-and-fill planning for land development, and measuring level differences in rice paddies and fields. It is also indispensable for cadastral surveys conducted by surveying firms and for producing accurate maps that form the basis of urban planning. In addition, RTK is used as control points for drone surveying, where it helps accurately convert aerial images into ground coordinates.

On civil engineering sites, construction quality can decline significantly without accurate RTK surveying. If a road’s slope is off by a few centimeters, drainage performance changes, and if a levee’s cross-section is not accurate, its disaster-prevention capability is compromised. For such high-stakes projects, RTK surveying is strongly required.

From the Perspective of Measurement Time and Work Efficiency

In GPS surveying, it can take several seconds to several tens of seconds for the receiver’s position to stabilize. When higher accuracy is required, you need to observe longer at the measurement point and collect data from multiple satellites. Recording positions while moving is possible, but, as with smartphone GPS, it is always accompanied by errors of several meters (several ft).

RTK surveying involves a process called initialization. This is a preparatory step to receive signals from a reference point and begin communication of correction information. Generally it is completed in a few seconds to a few minutes. Once initialization is complete, real-time position information with centimeter-level accuracy (half-inch accuracy) can be obtained. Subsequent measurement work is very fast. In layout work on construction sites, you can check the position with an RTK receiver each time you drive a reference stake, and because accurate positions are available almost in real time, work efficiency is greatly improved.

Differences in Impacts Caused by Environmental Conditions

One of the weaknesses of GPS surveying is its dependence on the environment. It does not function in environments where signals from satellites are difficult to reach, such as heavily wooded forests, urban canyons between buildings, or inside tunnels. Because accuracy degrades as the number of visible satellites decreases, practical precision can only be obtained in locations with a largely open sky.

RTK surveying also fundamentally depends on radio signals from satellites, but it is more resistant to environmental interference. Correction signals from reference stations are often transmitted via radio communications, and as long as you are within the range of those radio communications, it can operate under a range of environmental conditions. However, satellite signal reception remains an important factor for RTK surveying, and signals from multiple satellites are required, especially during initialization. Once initialization is complete, the correction signal can compensate for some degree of signal obstruction, so RTK can be used in a wider range of situations than GPS surveying.

Utilization of the Control Point Network and Measurement Areas

An important element when conducting RTK surveying is the reference point network. Reference point networks maintained by public agencies cover the major regions nationwide and, in many cases, are accessible to anyone. In areas where reference points are densely concentrated, more stable correction signals can be obtained, further improving accuracy.

The coverage of reference point networks and the distances between reference points vary by region. In urban areas they are often arranged densely, making them an ideal environment for RTK surveying. Conversely, in rural mountainous areas the distances between reference points can be larger, which may slightly reduce accuracy.

Before conducting RTK surveying in a new measurement area, it is important to check whether a usable control point network is available there. In areas where such a network is not established, you will need to consider options such as installing your own control points or using GPS surveying.

Technological Advances and the Utilization of NTRIP Streaming

In recent years, a major change has occurred in the practical operation of RTK surveying. Thanks to a technology called NTRIP (Networked Transport of RTCM via Internet Protocol), correction information from reference stations is now distributed over the Internet. This mitigates the physical limitation imposed by the radio communication range of reference stations.

If an internet connection is available, you can receive correction signals from reference stations located hundreds of kilometers away. Even consumer devices such as smartphones can now receive NTRIP streams over mobile networks and obtain high-precision positioning information. The proliferation of this technology is turning RTK surveying into a more accessible and user-friendly technique.

However, because it depends on an Internet connection, the stability of the communications environment is important. In places where communication infrastructure is not well developed, such as mountainous areas or at sea, corrections using conventional radio-based reference stations are necessary.

Examples of work requiring measurement accuracy

High-quality construction in the building industry has become difficult without RTK surveying. For example, precise elevation control is essential for embankment work in land development projects. Even a difference of just a few centimeters (a few in) can affect drainage slopes and lead to future ground settlement or drainage problems. By using RTK surveying to verify high-precision embankment heights at each stage of construction, you can ensure quality as designed.

In agriculture as well, RTK surveying is indispensable for realizing precision agriculture. By obtaining accurate elevation data for the entire field, irrigation water distribution and fertilizer application rates can be optimized. Accurate positioning information from RTK surveying also underpins the automation of agricultural machinery such as tractors.

From the standpoint of surveying firms, GPS surveying and RTK surveying are used selectively according to the accuracy requirements requested by clients. In the preliminary survey phase, GPS surveying is used, while final definitive surveys employ RTK surveying for precise measurements; it is common to operate with consideration for the balance between cost-effectiveness and accuracy.

Future Surveying Technologies and the Need for High-Precision Positioning Information

With the spread of autonomous driving technology and drones, the importance of high-precision positioning technology is increasing further. For autonomous vehicles and drones to reach their destinations accurately and operate safely, centimeter-level positioning accuracy (cm level accuracy, half-inch accuracy) is essential. For this reason, investment in and research on high-precision positioning measurement technologies, such as RTK surveying, are becoming more active.

Moreover, as responses to climate change become increasingly necessary, the acquisition and management of accurate topographic data are becoming ever more important. Precise topographic information obtained by RTK surveying is indispensable for flood risk assessment and landslide prediction. Use cases for RTK surveying in the field of disaster prevention are also increasing, and the development of public reference point networks is steadily advancing.

Until now, RTK surveying was a tool for specialized surveying firms, but thanks to the miniaturization of advanced systems and the enhancement of user-friendly software, it has become easier for general companies to adopt and operate.

Devices that enable high-precision positioning on smartphones

In fact, high-precision positioning technology using smartphones has been rapidly evolving recently. Conventional smartphone GPS offers meter-level accuracy (foot-level accuracy), but by attaching certain add-on devices to a smartphone, RTK surveying-level high-precision positioning has become possible.

These iPhone-mounted GNSS high-precision positioning devices receive correction information delivered via NTRIP and provide high-precision positioning data to applications through the smartphone. Unlike conventional professional surveying equipment, they can leverage smartphones already used in daily work, so the barrier to adoption has been greatly reduced.

Cloud integration is also straightforward, allowing collected location data to be analyzed and shared in real time. This speeds up on-site decision-making and significantly improves work efficiency. The infrastructure is increasingly in place so that, even without being a professional surveying contractor, you can obtain high-precision location information in-house whenever needed.

The combination of the versatility of smartphones and advances in high-precision GNSS positioning technology is making the use of location information more practical across various fields such as construction sites, agriculture, disaster prevention, and infrastructure management. Going forward, this technology will continue to spread, moving toward an era in which high-precision location information becomes the foundation of everyday operations.

Summary

GPS surveying and RTK surveying are both satellite-based positioning technologies, but they differ significantly in terms of accuracy, cost, and applications. GPS surveying is sufficient for rough position determination when meter-level accuracy is adequate, but RTK surveying is indispensable for tasks that require high precision, such as construction work and agriculture.

Until now, RTK surveying was an advanced technique used by specialist contractors, but the development of reference point networks and the widespread adoption of NTRIP streaming have made it a more user-friendly, more accessible technology. Furthermore, the emergence of GNSS high-precision positioning devices that can be attached to smartphones has created an environment in which businesses can easily utilize high-precision location information.

In future business development, acquiring accurate on-site location information will become increasingly important. By selecting and implementing appropriate positioning technologies according to your company's operations, you can strengthen competitiveness and improve operational efficiency.