Sensor Fusion based UAVs for GPS denied Environments

The newest work in the field argues about the arbiter. A framework published in Sensors holds GNSS measurements out of the fusion window until integrity has been assessed, then re-solves them as factors. Its check runs against visual-inertial odometry rather than against surveyed truth, so the reference for deciding whether a fix is good is itself a relative estimate with its own drift. It reports detection probabilities above 96% for gradual attacks at 0.5 m/s over a 10–15 second window.

FAST corners split on a quadtree for uniform distribution, KLT optical flow on an image pyramid, PROSAC outlier rejection, DBoW loop closure over BRIEF descriptors: that is one filing's entire front end, and none of those components is distinctive to it. IMU pre-integration is the universal interface. Inertial samples are integrated between image timestamps so the inertial term becomes a residual at camera rate, minimised by Mahalanobis distance against a marginalisation prior in a sliding-window solve. This is the piece that makes tight coupling tractable on flight hardware, and it is no longer where anyone claims novelty.

Exyn's public filings are the sole audited revenue base in this market, and they set the scale. The company raised roughly $19.4 million gross at its May 2026 listing; in the quarter to 30 June 2026 it reported 950,000 of revenue, down 30.1%, a gross margin of 46.9%, and a net loss of 6.9 million. Cash was about 7.8 million at quarter end and roughly 4.5 million by 19 August, with the company stating that this will not cover a year of operations, and its chief executive departing after an internal investigation.

The filing centre of gravity is Chinese and Indian academic and state institutions. The most active filers are IIT Hyderabad, an Indian autonomous-navigation technology hub, Northwestern Polytechnical University and State Grid, with provincial grid operators and municipal engineering institutes behind them. No European, American or Israeli inertial house appears among the significant filers.

The horizontal and vertical problems have different error sources — pressure, ground effect and terrain-model staleness on one side; cross-view matching failure on the other — and the filings increasingly solve them apart. One runs parallel bundle adjustment with a planar branch for horizontal position and a DEM branch for vertical, then arbitrates between them by re-solving on randomly sampled grid points and checking Euclidean consistency. Another scales the live image against the satellite tile using ground sampling distance, focal length and barometric altitude before matching at all, which turns height into an input to the horizontal solve rather than an output of it. A third corrects the barometer itself, using inertial speed and a wind estimate inferred from the differential RPM of the rotors.

The United Kingdom committed £155 million to positioning resilience, and the split is the most informative single allocation in this market: £71 million for an enhanced terrestrial ranging system, £68 million for a national timing centre, £13 million for interference monitoring and £3 million for space-based time transfer. None of it is for onboard multi-sensor fusion. The demand is real and quantified — a single day of satellite navigation outage is estimated at £1.42 billion to the UK economy, seven days at £7.64 billion — and the money went to timing and to a ground network.