For a vehicle using dead reckoning or some other type of navigation which accumulates error as the vehicle moves, this invention provides a simple, single-sensor, low-cost, highly-accurate system for correcting navigation errors. The system uses a marker structure with optical density which is formed from one or more periodic patterns. The vehicle's navigation computer records the density, measured by the sensor, as the sensor moves on a line over a marker at a known location, then it processes the recorded density function to get the correct navigation parameters. If the vehicle's usual path passes over a marker, that path can be used without change for acquiring navigation corrections.