alongtrack

Alongtrack, often written along-track, is a term used in navigation, geodesy, and remote sensing to describe the distance measured along a reference path. It is commonly paired with cross-track, which measures distance perpendicular to that path. Alongtrack is used to quantify progress along a route, to locate data points along a track, and to evaluate how far a moving object has traveled in the direction of the path.

In technical terms, if a reference track is defined by a polyline consisting of sequential points, the along-track distance of a position is the distance along the path from the start to the closest point on the path to that position (the projection of the position onto the track). The cross-track distance is the shortest perpendicular distance from the position to the track. When the projection falls beyond the end of the track, different implementations may treat along-track distance as the distance to the end or as undefined.

Common applications include aviation and maritime navigation, where along-track distance to a waypoint or to a route segment helps with guidance and timing. In satellite remote sensing and oceanography, along-track coordinates align with the orbital or transect direction, aiding data binning, averaging, and interpretation along the measurement track. In geographic information systems, along-track measurements support route analysis, progress tracking, and performance assessment along roads or trails. Units are context-dependent, typically meters, kilometers, or nautical miles.