crosstrack

Crosstrack, often used interchangeably with cross-track, is a navigation and robotics term describing the lateral deviation of a moving object from a prescribed path. It is defined as the perpendicular distance from the object's current position to the intended track, and it can be described with a sign indicating which side of the route the object is on.

In aviation and maritime navigation, the planned route is typically a great-circle track between waypoints or a defined flight plan. Cross-track error (XTE) indicates how far off the route the vehicle is at any moment and is commonly used to guide corrective action. A small XTE means the vehicle is close to the track; a larger XTE triggers interception or turning maneuvers to rejoin the route. Along with cross-track error, along-track distance measures progress along the route toward the destination.

Calculation methods vary by model and coordinate system. In planar, small-area contexts, XTE can be computed as the distance from the current position to the line through the start and end waypoints. On a spherical surface such as Earth, cross-track distance can be estimated with spherical trigonometry. A standard form uses the Earth's radius, the angular distance from start to the current position, and the bearings along and to the track: XTE = R * asin(sin(delta13) * sin(theta13 - theta12)), where delta13 is the angular distance from start to current, theta13 is the bearing from start to current, and theta12 is the bearing from start to end.

Applications of crosstrack occur in flight management systems, autopilots, autonomous vehicles, marine navigation, and robotics. It is a core metric for path-following control, enabling corrective guidance to minimize lateral deviation from a desired route. Related concepts include along-track distance and route interception.