# Definitions

â€śApparentâ€ť angles are relative to the casing of the receiver (i.e., are in the receiver coordinate frame).

â€śTrueâ€ť angles are transformed into the world coordinate frame using an internal Inertial Measurement Unit (IMU).

â€śHeadingâ€ť or â€śYawâ€ť is the direction the boat is pointed (assuming the receiver is mounted to the boat in the configuration show in the diagrams).

â€śAzimuthâ€ť or â€śBearingâ€ť is the direction (in the horizontal plane) to the transmitter (or â€śtargetâ€ť), relative to the direction the boat is pointed or to the earthâ€™s coordinate frame, as noted in the modifiers â€śtrueâ€ť or â€śapparentâ€ť given with the angle.

â€śElevationâ€ť is the angle up or down from the receiver to the transmitter as measured from the horizontal plane.

Important: Many angles in this document are expressed in mathematical conventional rotations referenced to the X axis (or â€śbowâ€ť) pointed East being 0 degrees. See â€śCompass vs. Math Anglesâ€ť for more information.

Angles in interface messages are always given in degrees.

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