Expert Opinions: Integrating inertial tech with GNSS

Q: What key aspects should product designers consider when integrating inertial technology with GPS/GNSS?

Jeremy Davis, Director, VectorNav Technologies

A: The availability and quality of GPS in the application is critical. Industrial-grade MEMS IMUs can provide survey-grade performance when high-quality GPS is continuously available, but even tactical-grade MEMS cannot provide more than a couple of minutes of GPS-denied navigation. The level of integration between the two technologies is also important. Even comparing two systems using the same sensors, the performance is highly dependent on the ability of the system designer to leverage their respective strengths.

Ryan Dixon, Chief Engineer, SPAN, NovAtel

A: Successful integration of inertial sensors with GNSS requires understanding both the goals and environment of the application. Consider the required accuracy of attitude and position, severity of GNSS obstructions, expected dynamics and environmental conditions. Tradeoffs in size, power and cost narrow the choices, but achieving the desired performance is more nuanced. Data sheets for IMUs can also be notoriously difficult to compare. My advice is to focus on the goals and listen to the experts.

Andrey Soloviev, Principal, Qunav

A: There is a clear need for reliable consumer-grade GNSS/INS in GNSS-degraded environments. In this case, two key aspects are: removal of measurement outliers, mostly caused by multipath; and adequate modeling of inertial errors. The first aspect is efficiently addressed via residual monitoring, especially with GNSS carrier phase. A 15-state INS error model is generally sufficient. Yet, modeling parameters and contribution of other terms such as axis misalignment must be evaluated using test data.