Course Over Ground (COG)

The direction of a vessel’s movement over the Earth’s surface at a given time.

Usually abbreviated COG, it is commonly calculated by GNSS from successive positions and expressed as a true direction. It differs from heading, which is the direction the bow points, and from track, which describes the path over a period or between positions.

COG incorporates the combined result of vessel motion through the water, leeway and current, but does not separately identify their causes. At very low speed or while stationary it may be unstable or meaningless because small position changes dominate the calculation.