These are the most common definitions in AHRS:
Altitude is the distance along the ellipsoidal normal between the surface of the ellipsoid and a point of interest above it.
Attitude is the orientation of a vehicle or other object relative to a known reference, which could be a frame, the horizon, a direction of motion, or even another object. The heading of the object cn be omitted in the definition of its attitude.
Body Frame matches the frame of the platform the sensors are mounted on. The origin coincides with the center of gravity of the platform. The Y-axis points forward of the moving platform, while the Z-axis points upwards. The X-axis completes the right-hand system pointing in traverse direction. Some literature names it b-frame.
Earth-Centered Earth-Fixed Frame (ECEF) has its origin and z-axis aligned to the ECI frame, but rotates along with the Earth. Therefore is Earth-Fixed. Some literature names it e-frame.
Earth-Centered Inertial Frame (ECI) has the origin at the center of mass of the Earth. The X-axis points towards the vernal equinox in the equatorial plane. The Z-axis is along the rotation axis of the Earth. The y-axis completes with a right-hand system. Some literature names it i-frame.
East-North-Up Frame (ENU) is an LLF with the X-axis pointing East, Y-axis pointing to the true North, and the Z-axis completes a right-hand system pointing up (away from Earth.)
Elevation is the height above or below a fixed reference point. In Geography, it is most commonly the height of a terrain above (or below) the sea level.
Geodetic (also ellipsoidal or curvilinear) coordinates in the ECEF are defined for positioning elements on or near the Earth.
Inertial Navigation System is a navigation architecture consisting of an IMU, and a computer to continuously estimate a device’s positoin and orientation using dead reckoning.
Latitude is the angle in the meridian plane from the equatorial plane to the ellipsoidal normal at he point of interest.
Local-Level Frame (LLF) is the local navigation frame, whose origin coincides with the sensor frame. Some literature names it l-frame.
Longitude is the angle in the equatorial plane from the prime meridian to the projection of the point of interest onto the equatorial plane.
Meridian is the half of a creat circle on Earth’s surface terminated by the poles.
North-East-Down Frame (NED) is an LLF with the X-axis pointing to the true North, Y-axis pointing East, and the Z-axis completing the right-hand system pointing Down.
Orientation is the rotation needed to place an object from a reference placement to its current placement, neglecting its position or location in space.
Rectangular coordinates in the ECEF represent position of a point with its x, y, and z vector components aligned parallel to the corresponding e-frame axes.
Strapdown INS has accelerometers rigidly mounted parallel to the body axes of the vehicle. In this application the gyroscopes do not provide a stable platform; they are instead used to sense the turning rates of the craft.
|AHRS||Attitude and Heading Reference System|
|AoA||Angle of Arrival|
|AoD||Angle of Departure|
|atan2||Arctangent (four quadrants)|
|AUV||Autonomous Underwater Vehicle|
|BIH||Bureau International de l’Heure|
|CIRS||Conventional Inertial Reference System|
|CRS||Conventional Celestial Reference System|
|CTP||Conventional Terrestrial Pole|
|CTRS||Conventional Terrestrial Reference System|
|DCM||Direction Cosine Matrix|
|DoD||Department of Defense|
|DoF||Degrees of Freedom|
|EGM||Earth Gravitational Model|
|EKF||Extended Kalman Filter|
|ESA||European Space Agency|
|GNSS||Global Navigation Satellite System|
|GPS||Global Positioning System|
|GTRF||Galileo Terrestrial Reference Frame|
|IAU||International Astronomical Union|
|IERS||International Earth Rotation and Reference Systems Service|
|IMU||Inertial Measurement Unit|
|INS||Inertial Navigation System|
|INU||Inertial Navigation Unit|
|CIRAS||Coriolis Inertial Rate and Acceleration Sensor|
|ITRF||International Terrestrial Reference Frame|
|MARG||Magnetism, Angular Rate, and Gravity|
|MOEMS||Micro-opto electromechanical Systems|
|PIGA||Pendulous Integrating Gyroscopic Accelerometer|
|SI||Système International d’unités|
|SOA||Silicon Oscillating Accelerometer|
|SVD||Singular Value Decomposition|
|TFG||Turning Fork Gyroscope|
|UAV||Unmanned Aerial Vehicle|
|UKF||Unscented Kalman Filter|
|WGS||World Geodetic System|
|WMM||World Magnetic Model|
|ZUPT||Zero Velocity Update|