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Cross-Track Error Calculator

Enter the start and end of a straight great-circle route and the position you are at. The page reports how far you lie left or right of the track, how far along the route you have come, the nearest point on the route and the distance still to run. Everything runs in your browser.

degrees, −90 to 90
degrees, −180 to 180
degrees, −90 to 90
degrees, −180 to 180
degrees, −90 to 90
degrees, −180 to 180
Enter a route and a position to see the cross-track error.

Cross-track distance is signed: a positive value means you are to the right (starboard) of the course from start to end, a negative value means you are to the left. Distances follow the great circle on a spherical Earth of mean radius 6,371 km, not a rhumb line, road or charted channel; magnetic variation, current and leeway are not modelled. Positions within half a metre of the track are shown as on track. This is a planning aid, not a primary navigation system. Nothing is stored and the page makes no network requests.