RTK technology in the application of engineering construction layout and comparison with total station
- Construction Layout
1.Definition
Construction layout refers to the construction of the building on the design drawing. According to a certain method, in the field measurement work, the actual process involves accurately locating the proposed design onto the actual construction site. During the layout process, construction projects often have complex and diverse characteristics, requiring the integration of multiple methods to determine the positions of points and lines corresponding to the buildings. The selection of layout methods depends on the type of construction, construction methods, construction locations, construction conditions, control point distribution, and accuracy requirements for layout. Therefore, layout personnel need extensive experience to choose the appropriate surveying methods and different combinations of station points. In this process, factors such as accuracy requirements, calculation tools, available instruments, control point distribution, and site conditions need to be considered.
2.Development of Layout Tools
Layout data is crucial in traditional engineering layout, where points or lines need to be surveyed and measured in relation to existing buildings based on the construction drawings, that is, to find the corresponding distance, elevation and angle, and then measure the point position and elevation through the traditional level gauge, theodolite and other instruments. Traditional layout methods have low accuracy and efficiency, which cannot meet the increasing demands of engineering construction. With the development of surveying technology, total stations were invented, enabling simultaneous angle and distance measurements. However, the emergence of Real-Time Kinematic (RTK) technology undoubtedly brought about a significant revolution in engineering layout. RTK is the latest achievement in Global Navigation Satellite System (GNSS) development, addressing the shortcomings of GNSS and offering advantages such as short processing time and high accuracy. It provides real-time centimeter-level positioning accuracy during operations, eliminates the need for control point setup, and saves a significant amount of resources, time, and effort in engineering projects. It can also be operated by a single person, bringing great convenience for the lofting work. RTK technology has been widely applied in engineering construction layout, providing great convenience for surveying professionals. However, the shortcomings of RTK technology have also been revealed. For example, RTK layout is susceptible to ionospheric interference during the 12:00-13:00 time period, and the initialization time of the equipment can be long or even fail to initialize. In environments with obstructions (such as densely built urban areas, mountainous areas, or forested areas), satellite signal strength is low. The stability is not high and can be affected by satellite conditions, weather conditions, and data link transmission conditions. Compared to traditional layout technologies such as total stations, the accuracy of RTK technology still needs to be improved. Identifying the shortcomings of RTK technology and making improvements to address these shortcomings is currently the main focus of RTK research.
Ⅱ.Comparison of Total Station and RTK Technology
1.Principles of Engineering Layout Methods
A total station can quickly measure the azimuth and distance between points, making it easy to conduct on-site layout by establishing the relationship between known points and points to be surveyed. RTK mainly consists of three components: a base station, a rover station, and software packages. The RTK operation mode mainly achieves the transmission of coordinate information and observations between the base station receiver and the rover station receiver. The rover station receiver combines the received data with its own collected observation data to form differential observations, performs real-time baseline solution, and calculates the relative position of the rover station to the layout point, providing guidance for layout operations.
2.Comparison of Layout Process between Methods
When using a total station for layout, it is required to have two or more control points with mutual visibility around the layout point. If control points are missing, two mutually visible known control points need to be surveyed around the layout point. The total station is set up on one of the known control points, the other known control point is used as the back-sighting direction point. Only then we can layout data by adjusting the forward distance and direction and setting the horizontal angle.
In RTK layout, a suitable control point is selected in a location that is easy to transmits signals to the rover station. After setting up the base station, seven transformation parameters are calculated to transform coordinate systems. Rover station calculates the geographic azimuth and distance between rover station and the layout point in real time. By continuously adjusting the azimuth and distance, the point position is finally laid out.
3.Comparison of Advantages and Disadvantages of Two Layout Methods
As a long-term used layout instrument, the total station has mature technological support and holds an important position in the field of measurement. However, with the development of technology, RTK technology has certain advantages compared to the total station. Unlike the total station, RTK technology does not require line of sight, making it suitable for operating in complex environments such as densely populated cities or forests. However, we also need to consider obstacles that may block GNSS satellite signals. In terms of measurement accuracy, RTK is better suited for large-scale measurements, while the total station is only suitable for small-scale control measurements. For national geological disaster investigations, for example, RTK technology may be more beneficial for the work. The efficiency of RTK technology is self-evident as it enables single-person operations, making it more adaptable to market demands. Currently, RTK technology has rapidly developed and has been wide applied in various fields such as geological disaster investigations and mine restoration, where its high efficiency plays a crucial role (see Table 1 for a comparison of the two layout methods).
| Comparison item | Total Station | RTK |
| Perspective requirement | Front and back vision is required | Zenith vision is required |
| Measurement accuracy | Small range control measurement | Large range measurement |
| Efficiency | At least 2 to 3 people | requires fewer people |
Ⅲ.Applications of GNSS RTK Technology
1.Application of RTK Technology in Highway Layout
RTK layout technology has made significant contributions in various fields, with the most extensive application being the determination of the planar positions of layout points in highway routes. After setting up the reference station and the rover station, select the “layout” function, input the coordinates of the desired layout points, choose the point layout function, enter the preset point number in the input interface, click the calculation function to calculate the navigation data, and display the position of the layout point in the center of the navigation map. When the actual position of the layout point coincides with the position of the RTK antenna, the location of the layout point is obtained.
2.Application of RTK Technology in Building Axis Layout
(1)Select the control network within the measurement area. Scientifically select the observation period, avoiding the period between 12:00 and 13:00 due to severe ionospheric interference. Use static positioning to establish a high-level control network and measure at least three known control points nearby for coordinate transformation, ensuring the uniformity of the adjusted network accuracy.
(2)Calculate the coordinates of the relevant points on the building axis. Calculate the coordinates of the points on the desired axis based on detailed planning maps, construction drawings, and overall planning maps of the first-floor plan, etc.
(3)For RTK positioning, select open and elevated locations without tall obstacles, which are good positions for choosing base stations, and ensure that the base station is as close as possible to the layout points. In addition, at least three control points should be found near the measurement area for three-parameter calibration in order to achieve centimeter-level accuracy of the measurement points.
(4)Static sampling point detection. Set up the device on both the higher-level known point and the point to be measured, with the observation time set to 30 minutes. Finally, transfer the observed data from the receiver to the computer and compare it with the coordinates of the relevant points on the building axis to statistically analyze the accuracy of the layout results.
Ⅳ.Future Application of RTK Technology: Construction of Continuously Operating Reference Stations (CORS)
With the rapid development and widespread application of GNSS technology, the role of RTK in urban surveying has become increasingly important. The construction of a continuous operating GPS positioning service system has become one of the development hotspots in urban GNSS applications. It is a comprehensive system of continuous operation satellite positioning services established in a country or region using a multi-base station network RTK technology. By connecting the reference station and the data center through Internet technology and data communication devices, the software processing of the reference station network generates a network system consisting of raw GNSS data and RTK correction data, providing all-weather field measurement, positioning, and layout operations for RTK. It features all-weather, fully automatic, real-time navigation and positioning functions. With only one RTK, it can perform real-time and rapid positioning, navigation, or post-positioning operations with millimeter-level, centimeter-level, decimeter-level, or meter-level accuracy in the field. It can meet the functional requirements of automatic identification, navigation, scheduling, and safety monitoring of various land, water, and air transportation vehicles within the coverage area. It can also serve high-precision short-term weather forecasting. The application of the reference station network technology will effectively solve the problems of effective measurement range of RTK, long-distance data communication, and reliability of results.
Ⅴ.GEO SMART‘s Continuous Innovation, Improvement, and Customer Service
RTK technology has addressed the limitations of traditional surveying methods and brought great convenience to engineering construction surveying. However, RTK still has several shortcomings that affect the progress and accuracy of construction projects. The accuracy of RTK surveying is compromised by ionospheric interference and a decrease in the number of available satellites, leading to longer initialization times and even cases where initialization cannot be achieved. Additionally, RTK is susceptible to obstructions, resulting in low satellite signal strength, poor stability, and vulnerability to satellite conditions, weather conditions, and data transmission issues. Compared to traditional surveying techniques like total stations, the accuracy of RTK still needs improvement.
To address these shortcomings of RTK technology, We are committed to optimizing various aspects of its products and technology through continuous improvement, innovative research, and development efforts.
Firstly, in terms of signal coverage and stability, We Are Followed continuously optimizes the hardware design of its receivers to enhance satellite signal acquisition and data processing algorithms, particularly in weak signal conditions. This includes improving the capability to resist multi path interference. We promote multi-constellation compatibility by integrating not only the GPS system but also other global satellite navigation systems such as GLONASS, Galileo, and BeiDou. This integration increases the number of visible satellites, reduces blind spots, and improves positioning continuity and reliability.
Secondly, upgrades the communication link to enhance the performance of the radio communication system. This involves adopting more advanced data transmission protocols and technologies such as 4G/5G networks, Wi-Fi, or proprietary long-range radios to ensure stable data links and expand the effective working range between base stations and rovers. also develops CORS (Continuously Operating Reference Station) systems and PPP-RTK technology based on internet cloud services. These technologies utilize wide-area differential correction information to address signal coverage issues in remote areas.
Lastly, we provide an after-sales service system to customers worldwide, offering fast and effective solutions and technical support. This includes software updates, troubleshooting device malfunctions, and providing technical guidance. We assist users in fully understanding the features and operational methods of RTK equipment and how to respond appropriately to limitations in different application scenarios.