In this blog post, we’ll explore how GPS technology has been utilized in our daily lives and across various industrial sectors, as well as the direction in which it is headed.
GPS (Global Positioning System) is a satellite-based positioning system developed in the United States. Today, there is likely no surveyor who is unfamiliar with the term GPS. This technology, which emerged in the late 20th century, is now deeply embedded in our daily lives. Beyond the field of surveying, GPS is widely used by the general public for applications ranging from car navigation and GPS-enabled smartphones to finding one’s way during outdoor activities. In this way, GPS has established itself as an essential tool in various aspects of life.
GPS is broadly composed of three main components. First, the space segment of the system consists of GPS satellites. There are 24 GPS satellites (21 operational satellites and 3 spare satellites) in orbit, circling the Earth every 12 hours. The orbital altitude is approximately 20,000 km. Six orbital planes (each containing four satellites) are arranged at equal intervals (60 degrees apart) and have an inclination of approximately 55 degrees relative to the equatorial plane. This configuration ensures that users anywhere on Earth always have access to between five and eight satellites. The precise placement and operation of the satellites are critical factors in ensuring GPS’s high reliability.
Second, the control segment consists of tracking stations located around the world, where the signals from each satellite are measured. These stations play a pivotal role in maintaining the accuracy of the GPS system and are responsible for precisely adjusting satellite orbits and clock errors.
Third, the GPS user segment consists of GPS receivers and user groups. GPS receivers convert satellite signals into estimated position, velocity, and time. Four satellites are required to calculate the four-dimensional coordinates of X, Y, Z (3D position) and time. GPS receivers are used for navigation, positioning, time synchronization, and other research applications. In particular, GPS technology has recently been utilized across various industries, significantly improving productivity and efficiency. For example, in agriculture, the concept of precision farming has been introduced, and automated systems using GPS contribute to the efficient management of crops and increased productivity.
GPS positioning determines location by measuring the distance between satellites and users. If the distances to three satellites with known positions in space are known, the user’s position can be calculated. The distance is determined by measuring the time it takes for a signal, transmitted at a precise moment by an atomic clock on the satellite, to reach the receiver. If the clock in the GPS receiver were perfectly synchronized with the satellite’s clock, the time it takes for the signal to travel could be calculated based on the time the signal arrives. However, it is nearly impossible to perfectly synchronize the clocks of the GPS receiver and the satellites. Therefore, a fourth satellite is required. In other words, four variables are set: the three-dimensional position coordinates of the GPS receiver (X, Y, Z) and the time difference between the two clocks. Signals are then received simultaneously from four or more satellites, and the equations are solved to determine these unknowns.
GPS has various characteristics. First, since GPS offers a wide range of accuracy—from a few millimeters to tens of meters—depending on the positioning method used, the appropriate method is selected based on the surveying objective. For example, when high accuracy is required, a static positioning method is chosen, which, although it requires significant time and effort, can achieve accuracy in the range of a few millimeters. Conversely, when there are many positioning points and the required accuracy is not particularly high, dynamic positioning is used to efficiently determine locations in a short amount of time.
Second, GPS can determine positions not only anywhere on Earth but also in outer space, provided satellite signals can be received, regardless of weather or atmospheric conditions. This demonstrates that it has fewer constraints compared to traditional surveying methods, which strictly require line-of-sight conditions. However, a clear line of sight to the sky is necessary to simultaneously receive signals from at least four satellites.
Third, it offers high accuracy relative to the length of the baseline. With traditional surveying methods, errors increase proportionally as the baseline length increases, but with GPS, the impact of baseline length is relatively minor. Of course, when the baseline is short, various sources of error are reduced, leading to increased accuracy. However, even during long-distance surveying where the baseline exceeds 10 km, the decrease in accuracy due to the increased baseline length is minimal.
In addition to these advantages, GPS is widely used in daily life due to its convenience, efficiency, and speed. Modernization efforts are underway to enhance GPS positioning performance. Furthermore, the EU is developing Galileo, and Russia is improving GLONASS, with plans to establish a system that utilizes these three satellite systems in a cooperative manner. Once such a satellite positioning system is established, it is expected to enable faster and more accurate positioning, leading to the efficient utilization of satellite positioning in a wider range of fields. These changes will particularly demonstrate their potential in advanced technology sectors such as autonomous vehicles and smart logistics systems. Therefore, acquiring a basic understanding of GPS—which will be used even more extensively in the future—will enable users to utilize it effectively.
