When purchasing a GPS system, it is really important to consider the limitations of the technology. When making a big investment in equipment, you need to ensure that it is going to do everything you need it to. In this article, we are going to go over what you need to understand before you jump into surveying with GPS.
Technological Limitations of GPS in Surveying
Challenges When Surveying Near Trees or Buildings
Mitigating Challenges in Urban and Foliage Environments
Point and Performance: A Balancing Act
When it comes to land surveying, accuracy and reliability are paramount. Surveyors have long relied on traditional methods, whether that involved total stations, or other optical instruments. but the advent of GPS technology has revolutionized the field. Nowadays, many are turning to Real-Time Kinematic (RTK) GPS systems to enhance precision and efficiency. However, like any technology, GPS surveying comes with its own set of challenges, especially for those purchasing their first RTK system.
In this blog post, we’ll explore the various technological limitations of GPS in surveying, the specific problems that arise when working near trees or buildings, and the important considerations regarding price points and performance. Our goal is to provide a comprehensive guide for beginners, helping you navigate the complexities of GPS surveying and make an informed decision when investing in an RTK system.
A typical map screen configuration during a survey. Points are recorded and displayed for the user, which can then be navigated to, or exported for other uses.
Basics of GPS Technology
Global Navigation Satellite Systems (GNSS) technology relies on a network of satellites that orbit the Earth. These satellites transmit signals to receivers on the ground, allowing them to determine their precise location. At the time of writing this article, for global users there are four main satellite constellations to consider, GPS (USA), Glonass (Russia), Beidou (China), and Galileo (EU). While the basic concept is relatively easy to understand, there are several factors that can affect the accuracy and reliability of your GPS measurements in the field.
Satellite Geometry
The configuration of satellites in the sky at any given moment, known as satellite geometry, plays a crucial role in GPS accuracy. Ideal satellite geometry occurs when satellites are widely spaced across the sky, providing strong, intersecting signals. Poor satellite geometry, where satellites are clustered together or obscured by obstacles, can lead to inaccuracies. See what that means for your receiver below.
These issues can be overcome relatively easily by returning at a different time of day, or by using a multi-constellation GNSS receiver. With the latest 7th generation RTK technology, like that found in the Hemisphere S631 limits the effect poor geometry by tracking more satellites.
This is a simplified 2D picture on how a GNSS receiver computes a position, with red x signifying the possible position. The position is triangulated based on the position of the satellites and signals received. In a poor geometric configuration, the triangulation leads to a large uncertainty. Good configuration leads to a more precise position by narrowing the possible options.
Atmospheric Conditions
In order to reach your receiver on the ground, GPS signals must travel through the Earth’s atmosphere over a distance of around 20,000+ km. Unsurprisingly, this can introduce errors into the position. This error is primarily down to the interaction of the ionosphere and the GPS signal.
The ionosphere contains a layer of charged particles (some very interesting chemistry involved, you can learn more here: The Ionosphere (UCAR)). These electrically charged particles can deflect and alter the signals broadcast by the satellites. As we saw in the Spring of 2024 where we had a high level of solar activity these effects can wreak havoc on GPS.
However, modern RTK engines are beginning to model the ionosphere, which helps to drastically reduce the effect of ionosphere.
Signal Multipath
Multipath occurs when GPS signals bounce off surfaces like buildings, trees, or even the ground before reaching the receiver. This reflection can cause the receiver to calculate an incorrect position. Multipath is particularly problematic in urban environments or areas with dense vegetation. In the next section, we are going to get more detailed on what this means for you.
Signal Obstruction and Loss
Surveying near trees or buildings presents significant challenges due to signal obstruction. Trees with dense foliage and tall buildings can block or weaken GPS signals, leading to a loss of accuracy or complete signal loss. This is particularly problematic in urban areas or forests where clear lines of sight to multiple satellites are hard to maintain. These issues are compounded by the multipath errors described below.
Multipath Errors
As mentioned earlier, multipath errors are a major concern in areas with reflective surfaces. Buildings, in particular, can create strong multipath signals by reflecting GPS signals multiple times before they reach the receiver. This can significantly distort the positioning data, leading to errors that are hard to detect and correct.
The composition of buildings and the number of leaves on trees greatly influences how dramatic this effect is. For buildings, in general, the more metal and glass the building is constructed of, the larger the number of reflected signals that a receiver will have to contend with. For trees, deciduous or leafy trees with broad leaves will cause more problems than coniferous or trees with needles.
In order to obtain a fix in urban or foliage heavy environments, users will want to have a receiver that is capable of receiving the maximum number of the latest signals from GPS, Glonass, BeiDou, and Galileo. Check out the below image for an idea what happens to satellite signals in an urban environment.
When in an urban environment, satellite signals can be blocked and reflected. Receivers need to be able to recognize which signals to use and which signals to ignore.
There are multiple things you can do while in the field to help improve your performance under trees and near buildings. By using these tips, you can reduce your time in the field while making more money with your equipment.
Best Practices for Minimizing Errors
Base Placement: In order to get the best performance out of your rover, you will want to place the base in a location with little to no obstructions between the receiver and the sky. This will ensure that the data the rover receives is of the best possible quality. This will give you the fastest possible fix time and repeatability between measurements.
Observation Time: Another method you can use to increase the accuracy of your point is to increase the number of observations taken at a point. This will average a number of observations, increasing the accuracy of your measurement.
Range of GPS Equipment Costs
High precision GPS surveying equipment varies widely in cost, from a few thousand to tens of thousands of dollars. Entry-level systems may offer basic functionality suitable for general tasks, while high-end systems provide advanced features and superior accuracy for professional applications. Understanding which type of system best fits your needs will help you avoid making a purchase you will regret.
Difference in Accuracy and Reliability Across Price Points
Lower-cost GPS units typically receive fewer signals and offer a poorer performance level in the above-described multi-path environments. High-end RTK systems, on the other hand, provide enhanced accuracy and reliability, often incorporating features like multi-frequency support, advanced signal processing, and better multipath mitigation.
Examples of Different RTK Systems
Entry-Level RTK Systems: Affordable units like the Emlid Reach RS2 offer good performance for their price, making them suitable for beginners or small-scale projects. They provide reliable centimeter-level accuracy in open areas but may struggle in obstructed environments.
Mid-Range RTK Systems: Older systems like the Trimble R8s or Hemisphere S321 systems offer a balance between cost and performance. They are designed for professional use, offering improved accuracy and reliability in more challenging conditions. Sporting older technology, they will not perform as well in difficult environments, but will be able to get the job done. Check out our videos comparing the R8 and S321 to the latest Hemisphere S631 RTK system.
High-End RTK Systems: Top-tier systems like the Leica GS18T, Trimble R12 and Hemisphere S631 all provide the highest level of accuracy and reliability, suitable for complex and demanding surveying tasks. These systems come with advanced features that significantly reduce errors in difficult environments and make surveying easier. However, these receivers are not all created equal. Check out the below videos comparing them to one another.
Advice on Choosing the Right System for Beginners
When choosing an RTK system, consider the following factors:
Budget: Determine your budget and look for systems that offer the best value within that range. Although used equipment may be initially less expensive, the loss in productivity compared to the newer equipment will cost you more in the long run.
Application: Consider the specific requirements of your surveying tasks. If you primarily work in open areas, an entry-level or used system might suffice. For more challenging environments, investing in a higher-end system is advisable.
Support and Training: Choose a system from a reputable manufacturer that offers good customer support and training resources to help you get the most out of your equipment. Here at Bench-Mark, we provide our Survey-Assistant.comtraining, online Zoom training sessions and live tech support with every RTK system that is sold.
GPS surveying has undoubtedly transformed the field of land surveying, offering significant benefits in terms of accuracy and efficiency. However, it is essential to be aware of the challenges and limitations associated with GPS technology, especially for beginners purchasing their first RTK system.
By understanding the technological limitations, such as accuracy issues and signal reliability, as well as the specific problems posed by surveying near trees or buildings, you can better prepare for and mitigate these challenges. Additionally, balancing the cost and performance of different RTK systems is crucial for making an informed decision that meets your needs and budget.
Ultimately, with the right knowledge and tools, you can overcome the challenges of GPS surveying and achieve precise, reliable results in your projects. Happy surveying!
2. Accuracy: Compared to a total station, a GNSS receiver will not be able to achieve the same level of accuracy over short distances. Over short distances a total station is able to achieve accuracies in the range of singular millimetres. An RTK receiver at best will be able to achieve 8 mm of accuracy.
As technology continues to evolve, the potential for further enhancements in tilt functionality within RTK receivers is promising. Future iterations may focus on refining tilt capabilities, improving accuracy on extreme slopes, and expanding compatibility with other surveying tools and software.
The integration of tilt functionality into RTK receivers represents a significant leap forward in surveying technology. It addresses longstanding challenges in measuring points on slopes and uneven terrain, offering enhanced accuracy, efficiency, and safety. With its versatility and potential for further advancements, tilt-enabled RTK surveying is poised to redefine the landscape of modern surveying practices.
GPS (Global Positioning System) provides location and time information using a network of satellites. Standard GPS systems can achieve accuracy within a few meters, which is suitable for general navigation but not for precise surveying tasks.
RTK (Real-Time Kinematic) GPS, on the other hand, uses a fixed base station and a rover to provide real-time correction signals, achieving centimeter-level accuracy. This high precision makes RTK GPS ideal for surveying, mapping, and other applications requiring exact measurements.
Improving GPS accuracy in challenging environments involves several strategies:
Antenna Placement: Place your GPS antenna in the clearest possible area to minimize signal obstruction.
Observation Time: Extend the observation period to allow for more data collection, which can help average out errors.
Advanced Equipment: Invest in higher-end RTK systems that offer better performance in obstructed environments.
Budget: Determine how much you are willing to invest and seek systems that offer the best value within that range.
Accuracy Requirements: Assess the level of precision needed for your projects. For basic tasks, an entry-level system may be sufficient, while complex tasks may require a higher-end model.
Environment: Consider the environments in which you’ll be working. Dense urban areas or forests may necessitate advanced features for better performance.
Support and Training: Opt for a system from a reputable manufacturer that provides good customer support and training resources.
Future Needs: Think about potential future requirements and choose a system that can scale with your needs.
Bench Mark Equipment & Supplies is your team to trust with all your surveying equipment. We have been providing high-quality surveying equipment to land surveyors, engineers, construction, airborne and resource professionals since 2002. This helps establish ourselves as the go-to team in Calgary, Canada, and the USA. Plus, we provide a wide selection of equipment, including global navigation satellite systems, RTK GPS equipment, GNSS receivers, and more. We strive to provide the highest level of customer care and service for everyone. To speak to one of our team today, call us at 403-286-0333 or email us at [email protected].
Canada’s #1 supplier of land surveying equipment and instruments.
