- The most dangerous thing a GPS-denied drone can do isn't drift. It's report a confident position that's wrong. A better estimator won't fix that, because "can I trust this position?" is a different question than "what is this position?" 🧵
- We built Lodestar around that second question. It runs a real tightly-coupled VIO EKF for accuracy. But the durable part is a navigation integrity monitor that sits outside the estimator and grades every position GREEN, AMBER, or RED.
- Why outside? Trust must not depend on the thing being trusted. An estimator scoring its own output will rationalize a bad fix, the way a witness shouldn't certify their own testimony. So the monitor is separate code watching for when no position could be trusted at all.
- It fuses three signals with hard thresholds, no learned score: usable feature count (GREEN >= 8, RED < 1), position sigma (GREEN < 0.6 m, RED > 1.5 m), and vision NIS, the chi-square innovation consistency check (GREEN < 7.0, RED > 30.0). Fully deterministic.
- In the seeded mission the case that matters is a pitch-black tunnel where visual features collapse to near zero. Stock VIO would still emit a confident pose, straight into a wall. Our monitor flips RED, holds it 0.5 s to debounce, and triggers return-to-home at t=52.5 s.
- That's the whole thesis: the system abstains. It says "I can't trust this" and flies home instead of bluffing a fix. On the seeded mission it flags the unobservable tunnel 100% of the time, with 0.1% false alarms on the healthy GPS-denied leg.
- And it isn't trading accuracy to get there. Through the jamming bubble the track holds ~0.9% drift on a 245 m path, where dead-reckoning blows out to 31%. Accuracy and honesty from separate parts of the stack. (One seeded synthetic mission, ground truth made independently.)
- If you build SLAM or VIO: would you let the integrity check read the estimator's internals, or keep it strictly outside on independent signals? We chose strictly-outside on purpose. Where would you draw that line? #VIO #SLAM #DroneAutonomy #GPSdenied
- Full flight replay, the benchmark scoreboard, and the one-click Flight Integrity Report (with an honest stubbed-vs-deferred scope disclosure) run in the browser here: veriprajna.com/demos/gps-denied-drone-autonomy
Published on X · July 30, 2026
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