A computer includes a processor and a memory storing instructions executable by the processor to determine an estimated pose of a vehicle in a global reference frame having a first error and to determine an estimated second error based on a combination of the first error and a map error, in which the map error represents a difference between the estimated pose of the vehicle in the global reference frame and a corresponding estimated pose in a map-referenced frame. The stored instructions being additionally to predict a third error in a future map-referenced measurement frame based on the estimated second error and a motion model and to compute an update to the third error by combining the predicted third error with an accumulation of instantaneous vehicle position and heading errors obtained via a comparison between a camera-observed feature and a corresponding feature from a digital map.