Quadrantal bearing system or Reduced bearing. This method is used to measure a line’s bearing relative to another fixed point or object. In this method, the Prismatic Compass is graduated.Įxample: If a line makes up part of the circumference of a circle, its bearing would be the angle it makes with that circle’s center. As a result, the bearing’s value ranges from 0 to 360 degrees. In this system, the bearing of a line is measured clockwise from magnetic north.

Fore Bearing (FB) or forward bearing (FB).

The common bearing designations used in surveying are: The true bearing and magnetic bearing are determined from the grid bearing by subtracting or adding 35° respectively. The grid lines are chosen in such a way that they are parallel to the meridians and perpendicular to the parallels.Ī line’s grid bearing is its horizontal angle with a grid line running through one of its extremities. It is measured with a theodolite or sextant.Ī grid bearing is measured using the direction northwards along the grid lines of the map projection as a reference point. These meridians are used to identify the relative positions of lines in a small area.Īrbitrary bearing: A line’s arbitrary bearing is the horizontal angle formed by any arbitrary meridian passing through one of its extremes. It is measured with a magnetic compass.Īn arbitrary meridian is any convenient direction towards a permanent and prominent mark or signals, such as a church spire or the top of a chimney.

Magnetic bearing: A line’s magnetic bearing is the horizontal angle formed by the magnetic meridian passing through one of the line’s extremities. A magnetic compass can be used to determine the direction of the magnetic meridian. The magnetic bearing through a point is the direction represented by a freely floating and balanced magnetic needle free of any other attractive forces. Because the real meridian through a point is constant, the true bearing of a line is a constant amount. True Bearing: The correct bearing of a line is the horizontal angle formed by it with the true meridian at one of its extremities. Astronomical observations can be used to determine the direction of the real meridian through a point.

As a result, it travels through the true north and south. True meridian through a point is the line formed by a plane passing through the true north and south poles and intersecting the earth’s surface. A meridian is any direction, including True meridian, magnetic meridian, and arbitrary meridian. Bearings are most commonly used when measuring slopes or drain lines.Ī line’s bearing is its orientation in relation to a certain meridian.

Relative bearing and true bearing