unmanned aircraft, relative navigation, GPS denied environments


For unmanned aircraft systems to become fully integrated into society, safe and reliable methods for estimation and control are required even when global measurements such as GPS are degraded or unavailable. In these situations, estimating the vehicle's global state directly leads to inaccuracy and inconsistency. The relative navigation framework avoids these issues by estimating the vehicle's state with respect to a current local coordinate frame associated with a visual odometry algorithm. A globally consistent and localized pose-graph map is produced by compounding these local estimates and opportunistically incorporating additional constraints such as GPS measurements and loop closures. This architecture increases the safety and performance of the system by decoupling critical tasks, such as stabilization and obstacle avoidance, from tasks such as global map optimization and mission planning that are more computationally intensive and can produce discontinuities. The architecture and components of the general relative navigation framework are described, and hardware results are presented for an example multirotor implementation.

Original Publication Citation

Wheeler, D., Nyholm, P., Koch, D., Ellingson, G., McLain, T., Beard, R. Relative Navigation in GPS Degraded Environments, Encyclopedia of Aerospace Engineering: UAS, Wiley, May 2016, DOI: 10.1002/9780470686652.eae1154.

Document Type

Book Chapter

Publication Date


Permanent URL


John Wiley & Sons




Ira A. Fulton College of Engineering and Technology


Mechanical Engineering

University Standing at Time of Publication

Full Professor