In those circumstances, a GNSS device with two antennas can be used instead.Ī bearing is the direction from one place to another, measured in degrees of angle with respect to an accepted reference line. However, only the best IMUs are able to do this well at low speed. Typically, heading determination is the job of the IMU. For example, on a boat the helmsman may be trying to steer a course of 180°, but the heading one moment is 188° and the next moment it is 074°.

It is a constantly changing value as a vessel yaws back and forth across the course due to the combined effects of sea, wind, and steering error. It is expressed as the angular distance relative to north, usually 000° at north, clockwise through 359°, in degrees of either true, magnetic, or compass direction. Heading is the direction in which a vehicle/vessel is pointing at any given moment. On a GPS receiver, the actual direction of motion is called course over ground (COG) or, on some units, track. Ideally (but rarely) it is the same as heading. The course is the intended direction of travel. Applanix systems integrate precision GNSS with advanced inertial technology to provide uninterrupted measurements of the position and attitude of moving vehicles and vessels.Ĭourse, heading, and bearing, are key navigation concepts. ĭetermining and tracking the position, heading, speed, and attitude of a vessel requires a combination of a GNSS receiver and an inertial measurement unit (IMU). This requires knowing the vessel’s attitude (roll, pitch, and yaw). If a remote sensing device-such as a multispectral camera or an imaging LiDAR-is rigidly attached to a vessel (as opposed to being gyro-stabilized), it is essential to know the direction in which it is pointing at any given moment. Additionally, a vessel’s heading and, ultimately, its course are affected by steering error. (In the ocean, most currents flow in the general direction of the prevailing wind, so these problems tend to be additive.) A boat or ship’s helmsman or autopilot, an aircraft’s pilot or autopilot, and a UAV’s autopilot are constantly making small corrections to keep the vessel pointed in the right direction-yet none of them can keep precisely on course all the time. All vehicles and vessels (boats, ships, etc.) are affected by the speed and direction of the wind those on the water are also affected by currents and waves. This is particularly true in the air and on the water, where there are no roads to constrain travel.

Navigation requires knowing the lay of the land one’s position, heading, and speed and how they are being affected by external forces.

Relative bearing and true bearing