VRS vs Nearest Point Networks: A Comprehensive Guide for Land Surveyors

In the world of land surveying, achieving pinpoint accuracy is essential. Real Time Kinematic (RTK) Global Navigation Satellite Systems (GNSS) have made surveying more efficient, but their ability to get around terrain or long distances with just UHF radio can sometimes leave the surveyor stuck in a ditch. This is where network correction services come into play, helping surveyors enhance the precision of their positioning systems using a cellular network instead of UHF. Among the most widely used correction methods are Virtual Reference Stations (VRS) and Nearest Point Networks (often referred to as single-base corrections).

Understanding the key differences between these two systems is vital for surveyors to make the right choice for their projects, depending on factors such as project scale, accuracy needs, budget constraints, and available infrastructure. This article provides a comprehensive comparison of VRS and Nearest Point Networks, diving deep into their functionalities, advantages, and limitations, to help surveyors select the best option. Don’t want to read? Check out our video below:

Virtual Reference Stations (VRS): Work Anywhere

Advantages of a VRS Network

Disadvantages of a VRS Network

Nearest Point Network (Single-Base Correction)

Advantages of Nearest Point Network

Disadvantages of Nearest Point Network

When to Choose a VRS Network

When to Choose Nearest Point Network

Technological Trends and Future Considerations

Key Differences Between VRS and Nearest Point Networks

Conclusion

Virtual Reference Station (VRS) Networks: Work Anywhere

A Virtual Reference Station (VRS) is a correction service that uses a network of continuously operating GNSS reference stations (CORS) to create a virtual base station near the user’s rover. This technique is typically part of a Real-Time Kinematic (RTK) Network and is designed to provide highly accurate positioning data to surveyors. 

VRS networks are especially suited for covering large areas, with many nationwide networks using a backbone built upon VRS software. Networks include not only subscription based networks like Leica’s Smartnet and Trimble’s Cannet, but also public networks like Ohio’s ODOT VRS and South Carolina’s SCRTN networks. 

How a VRS System Works

The concept behind VRS is on paper very simple. A central server collects all available data from a network of base stations locations. This data is then input into a computer program to simulate the presence of a physical reference station near the GNSS rover, even though no such physical station exists on-site. The server then transmits data based on this simulated position to the rover, allowing it to calculate a fixed position. The VRS system uses the following process:

1. This process allows the rover to function as if it were near a real base station, ensuring high positional accuracy across the entire network coverage area.
   
2. The surveyor’s GNSS receiver (rover) determines its approximate location using satellite signals.
   
3. This position is sent to the central processing server, which collects data from multiple reference stations in the area.
   
4. The server calculates the GNSS correction data based on the rover’s location and creates a virtual reference station very close to the surveyor’s receiver.
   
5. The server transmits the correction data back to the GNSS rover, which applies the corrections to compute accurate real-time positions.

Advantages of a VRS Network

Enhanced Accuracy Across Large Areas

The biggest advantage of VRS is its ability to provide consistent accuracy across a wide area. By generating a virtual reference station close to the user, it minimizes errors that increase with distance from a physical base station. For operators working over a large area this can help keep data consistent from site to site. 

Convenience and Reduced EquipmentSince the system creates virtual reference stations, surveyors no longer need to set up their own physical base stations. This simplifies gear requirements, reduces setup time, and decreases the amount of equipment required for the job. For operators who need to visit multiple sites every day, this is a great solution.  

Disadvantages of a VRS Network

Subscription Costs

Depending on where you are, access to a VRS networks can come with a subscription fee, which can be costly. For smaller firms or projects with limited budgets, these fees can become incredibly taxing as they add up year after year for a project. We have had users with over $35,000 a year in subscription costs, who switched away from a VRS due to these costs. 

Network Dependency

The capabilities of a VRS network can be heavily dependant on factors out of a surveyor’s control, such as network base issues or downtime, or changes in position day to day if the network drifts. These issues are the hardest to overcome because they are out of your hands and put you at the mercy of the staff operating the VRS network.

High Infrastructure Requirements:

VRS networks rely on a dense array of GNSS base stations, sophisticated central servers, and reliable data connections. Depending on the network, coverage may not be available in more rural or remote areas, making it hard to do work outside of urban centers. On top of this, as technology progresses, the larger the number of base stations in a network the higher the cost to upgrade. This means that technology can be out of date, not giving you the best performance. 

Nearest Point Network (Single-Base Correction)

The Nearest Point Network, often referred to as single-base correction service, uses correction data from the closest physical reference station to the rover. This approach is still widely used, especially in areas without VRS network coverage, or where higher accuracy and redundancy is required. Corrections can be broadcast over either UHF or via cell networks. For the network component we obviously need to use a cell network. An example of a service that allows you to run your own Point to Point network is StormCaster.

How Single-Base Correction Works

In a single-base correction system, just like a standard base and rover setup, a GNSS base station is installed at a known, fixed location. The base station continuously tracks GNSS satellite signals and sends out correction data for rover use. This data is then transmitted to the rover in real time. Here’s how the process works:

1. The base station receives signals from GNSS satellites and broadcasts real time corrections to a network location, typically an NTRIP server.
   
2. The NTRIP server sends these corrections to the rover via internet connection.
   
3. The rover uses the correction data to adjust its positional calculations, improving accuracy relative to the base station’s location.
   
4. Unlike VRS, the correction data comes from a single, static point, and the accuracy of the corrections is based on the distance from the station rather than network conditions.

Advantages of Nearest Point Network

Simple and Easy to Use

Single-base systems are straightforward to set up and operate. Surveyors only need access to one base station, making this a convenient solution for surveyors who have the majority of their work in a local area, or a long-term job site that could have a permanent base setup.

Lower Cost

Since single-base systems don’t rely on an extensive network of base stations so they are often significantly less expensive than a VRS system. This makes them a good choice for smaller firms or projects with limited financial resources but many machines on site. The software that is required to run a VRS network can cost upwards of $100,000.

Availability in Remote Areas

In regions where VRS networks are unavailable or impractical, single-base correction can still provide reliable positional data, with a much simpler deployment procedure. This means that smaller communities or municipalities can deploy a single point reference station much quicker than building up the resources to implement a VRS.

Disadvantages of Nearest Point Network

Accuracy Diminishes with Distance

The primary drawback of single-base systems is that their accuracy decreases as the rover moves farther away from the reference station. This is due to spatial decorrelation, where satellite signal errors (such as atmospheric delays) differ over longer distances. This means that a single-base system is not suited for survey firms that send their crews over a large area to do work. See our video below on accuracy at distance.

When to Choose a VRS Network

Large-Scale Projects

One of the primary advantages of VRS systems is their ability to deliver consistent accuracy across large geographical areas. For projects that cover extensive regions, such as infrastructure development, VRS is an ideal choice. The system’s ability to create virtual base stations near the rover ensures that accuracy is maintained regardless of the rover’s movement across the project.

Urban Areas with Strong Network Coverage

Urban areas often have strong network coverage for VRS and great cell network coverage, making VRS a great choice for large projects in densely populated cities. VRS networks are particularly well-suited to urban environments, where multipath errors and signal interruptions are common due to tall buildings and dense infrastructure. Because VRS uses data from multiple reference stations in the area, it can mitigate these errors better than single-base systems, which rely solely on data from the nearest reference station.

When to Choose Nearest Point Network

Small or Localized Projects

For small projects with limited geographical scope, a single-base correction system is often sufficient. Tasks such as boundary surveys, site layout for smaller construction projects, or agricultural mapping can be completed using a single reference station. As long as the rover stays within a reasonable distance of the base station (typically up to 10-20 kilometers with a 7^th generation RTK receiver), accuracy will remain high enough for most practical applications.

Remote or Rural Areas

In areas where VRS network infrastructure is sparse or unavailable, single-base systems provide a reliable alternative. Rural and remote regions, where VRS coverage is limited or nonexistent, can still benefit from high-accuracy GNSS corrections using local reference stations.

Budget-Conscious Projects

Single-base correction systems are generally less expensive than VRS, making them an attractive option for projects with tight budgets. For organizations that cannot afford the subscription fees associated with VRS networks, single-base systems provide an affordable way to achieve reasonably accurate positioning without breaking the bank.

Technological Trends and Future Considerations

As GNSS technology continues to evolve, both VRS and single-base correction systems are becoming more sophisticated. Advances in satellite constellations, such as the addition of new GNSS signals from systems like Galileo or BeiDou and the addition of forward error correction on GNSS signals, are improving the overall availability and accuracy of satellite positioning data. These improvements are expected to enhance both VRS and single-base systems in the coming years.

Integration with UAVs and Automation

Surveying technology is also advancing rapidly in the areas of automation and unmanned aerial vehicles (UAVs). Both VRS and single-base correction systems are being adapted for use with UAVs, which can carry GNSS receivers to collect topographic data over large areas. As drone technology becomes more integrated into land surveying workflows, the demand for accurate, real-time corrections will continue to grow, and both VRS and single-base solutions will play important roles in supporting these automated systems.

Key Differences Between VRS and Nearest Point Networks

While both VRS and Nearest Point Networks provide GNSS corrections, they do so in fundamentally different ways. Here’s a detailed comparison of the two:

Conclusion

Both VRS and Nearest Point Networks offer valuable GNSS correction methods for land surveyors, but the choice between the two depends on specific project requirements. VRS excels in providing uniform coverage over large areas but comes with higher costs and infrastructure requirements. Nearest Point Networks, while simpler and more cost-effective, have limitations when it comes to accuracy over long distances and coverage areas.

For surveyors working on large-scale projects or in areas with good network coverage, VRS offers more uniform precision and ease of use. On the other hand, for small, localized projects or in regions where budget constraints or network availability are concerns, a single-base correction system can provide accurate results at a lower cost.

By understanding the strengths and weaknesses of each system, surveyors can make informed decisions that best meet their project needs, ensuring efficiency, accuracy, and cost-effectiveness in their work.

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 +1 (888) 286-3204 or email us at [email protected]