From u-blox.com: “3-Dimensional Automotive Dead Reckoning (“3D ADR”) aids traditional GPS/GNSS navigation via intelligent algorithms based on distance, direction and elevation changes made during satellite signal interruption.”
As shown in the video, given that errors in such a system are cumulative, u-blox’s 3D ADR is amazingly accurate, perhaps even comparable to military inertial guidance systems.
See on www.youtube.com