HOW BEST TO DEPLOY BASE STATIONS AND VIRTUAL REFERENCE STATIONS
Land surveyors have been using GPS receivers at a known position, called base stations, for a long time, and that method continues to be effective and used a lot. However, there's also the option of using a virtual reference station (VRS) instead of a base station. A VRS is a technique for network real-time kinematic (RTK) for GPS systems. How do you choose between a base station and a VRS? Well, there are pluses and minuses with each system, so it depends.
Base Stations and VRS - 101
Base Station
A base station is a GPS receiver placed at a fixed location. It gets correction information for nearby portable GPS receivers. Without these corrections, the location accuracy of the GPS receivers would not be as precise. The correction data allows any effect obtained by the mobile stations to be corrected out of the position data. There are some cons when it comes to using base stations. The first one is that they must be manually set up, which can be time-consuming. Another drawback is that they are limited to radio broadcast orbits that are shorter than cellular-based VRS networks. Virtual Reference Stations connect through cell coverage and produce highly accurate results. So, unless you're in a cellular dead zone, you can quickly and easily connect to the VRS system, such as Trimble's VRS Now. This VRS method is a highly accurate and effectively managed solution. A VRS's primary objective is to reduce the baseline distance between the rover and the reference station to efficiently remove spatially correlated errors. The process begins with the data from the reference stations being transmitted to the processing and control center at a one-second interval. The RTK user sends their approximate position to the processing center, which determines which triangle the user is stationed at, computes the imaginary VRS, and transmits the data to the user. The interpolated data obtains the correction data for the rovers, reducing the RTK measurement's systematic influences. VRS' GPS accuracy is between one and two centimeters. Reaching this level of accuracy requires precise dual-frequency carrier-phase observations, which are processed using a differential GNSS algorithm such as RTK or post-processing (PP). GNSS networks make it possible to use multiple reference stations, which results in more exact data modeling of distance-dependent systematic errors. The GNSS network can decrease the dependence of the error budget on the distance of the nearest antenna.
Which is the Better Method? It depends
VRS
Choosing between using a base station or a VRS isn't necessarily difficult, but depending on your needs, one could be a better fit for you than the other. The VRS network certainly comes with a few more advantages. For example, with a VRS subscription service, you can connect your machine or rover with the VRS network (modem with sim card). Using VRS is typically quicker because you don't need a base station set up on every job, allowing you to move between different job sites without lugging around a base station with you. Base stations are also costly, limiting the number of jobs you can work on at once. For example, if you have a fleet of 5 GPS-equipped machines but only two base stations, without VRS, you could only work two jobs at a time. With VRS, you are only limited based on the number of VRS subscriptions you have. This approach means that you would need five subscriptions if you wanted to have all machines run off VRS simultaneously. We like the hybrid approach - have one or two base stations for use on your larger jobs and use VRS on your smaller jobs. This solution allows you the flexibility of owning a couple of base stations and a couple of subscriptions and deploying them efficiently around the job sites.
Still Unsure? Contact ECI!
Our team of engineers has seen it all and can answer any specific questions you may still have surrounding base stations, VRS, or any other GPS-related component for construction equipment. Contact us via phone, email, text, website, or social media. Let's get your earthwork more efficient starting today!