. In fact, some services now provide centimeter level performance, in under a few minutes. This has brought PPP forward as an option for precision applications such as agriculture and automotive.
Choosing a GNSS Corrections Service
How do you choose which correction type to use?
When comparing correction types, you want to ask, what corrections are available near you? What are your hardware and infrastructure requirements? What kind of correction source reliability you need?
Each correction type has benefits and limitations, and their use ultimately depends on your application requirements. Some users choose to use multiple correction sources to provide extra coverage, redundancy and reliability.
Regardless of which service you choose, the additional information supplied by corrections all improve the GNSS position calculated by your receiver.
That concludes our section on reducing errors through GNSS equipment and correction services. Our next episode will describe how to use additional sensors like inertial navigation systems to enhance your position even further. If you’re ready to start learning these GNSS concepts, you can download our book An Introduction to GNSS.
Hexagon | NovAtel positioning product manager, agriculture, Haley Lawrance describes how inertial navigation systems can be combined with traditional GNSS for enhanced positioning in episode five of our on-demand webinar series. She demonstrates how INS use inertial measurement units to understand motion, and outlines several methods of sensor fusion.
Hello, and welcome to episode five of NovAtel’s webinar series on An Introduction to GNSS. My name is Haley Lawrance; I’m the positioning product manager, agriculture at NovAtel, part of Hexagon. Thanks for joining me!
So far, the series has demonstrated and explained calculations and technologies behind GNSS, so you now should have solid foundational understanding of satellite positioning. Last episode, Jenn reviewed how we resolve positioning errors through GNSS equipment and infrastructure. Another way to resolve errors and further finesse your position is by using additional sensors like inertial navigation systems.
In this episode, I’ll explain inertial navigation systems, sensor fusion, and how additional systems work to complement GNSS positioning. If you’d like to read ahead about these technologies, download our free book, An Introduction to GNSS.
What are Inertial Navigation Systems?
An inertial navigation system uses rotation and acceleration information to understand your movement in a three-dimensional space. It calculates your position, velocity, and attitude in relation to an external reference. The system uses inertial measurement units (IMU) to calculate your precise relative movement over a period of time. An IMU includes a gyroscope and accelerometer on each of the three orthogonal axes. These sensors measure rotational and linear acceleration, so that the INS can use these measurements to determine position, velocity, and attitude, including roll, pitch, and azimuth.
But, IMUs still need an external reference in order to determine your location on the Earth. The INS on its own can only provide measurements in reference to itself. In order to understand where it is situated in 3D space, it requires an external reference. That is where GNSS comes in.
Combining GNSS and INS
Both GNSS and INS positioning have benefits and limitations. As we’ve seen in past episodes, GNSS positioning delivers latitude, longitude, and height positioning nearly anywhere in the world, but you need to have direct line of sight to at least four satellites. You can have meter to centimeter-level accuracy, but that varies and is even disrupted as a result of signal blockages, multipath, and atmospheric delays.
INS calculates the change in position based on its own direction and orientation measurements, but requires an external reference for those measurements to be applicable to the environment. As with any system, errors are present; for INS, sensor errors inherent to the IMU can cause position drift over time and 