bearingtrue

Bearing true, often written as bearing true or true bearing, is a navigation and surveying term that denotes the direction of a line or object measured relative to true north—the direction toward the geographic North Pole. It is distinguished from magnetic bearing, which uses magnetic north as the reference, and from grid bearing, which uses a map grid. A true bearing is expressed as an azimuth: an angle in degrees clockwise from 0° at true north to 360°.

In practice, bearing true is used for determining courses on long-distance travel or for mapping, where reliance on a magnetic reference would introduce errors due to magnetic variation. To obtain a true bearing from coordinates, one computes the azimuth from the starting point to the destination using geographic or projected coordinates, typically with a GPS, GIS software, or a surveying calculator. For small areas a planar approximation may be sufficient; for longer distances, great-circle calculations are used.

Converting a true bearing to a magnetic bearing requires knowledge of the local magnetic declination (variation), which is the angular difference between true north and magnetic north. Magnetic bearing = true bearing minus declination (east declination decreases the bearing; west declination increases; signs depend on convention).

In practice, professionals record whether a bearing is true or magnetic to avoid misinterpretation, and many field devices allow the user to toggle between references.

This concept is fundamental in navigation, surveying, aviation, and cartography, where precise directional information anchored to a non-movable reference frame—true north—is essential.