The orientation model in SDX

This document explains which type of angles are used, in SDX, for the 6 degrees of freedom (6DoF) features for GNSS receiver body orientation.

SDX uses the Tait-Bryan angles, also known as nautical angles. From this type of formalism, there are two conventions that are found in navigation:

  • z-y’-x’’ intrinsic rotation
  • z-x’-y’’ intrinsic rotation

In the SDX simulator, we use z-y’-x’’ intrinsic rotation. The rotation angles are yaw, pitch and roll, in reference frame NED. The x axis points North, the y axis points East, and the z axis points towards the center of the earth.

Illustration demonstrating rotation angles (yaw, pitch and roll) in reference frame NED (North, East, Down)

The first rotation is around z axis, the second around y axes and the third around the x axes. This transformation is also known as 3-2-1.

The antenna is boresight along the negative Z-axes (maximum antenna gain is oriented to -Z direction).

When the angular offsets between the body frame and NED are zero, the two frames are aligned.

Antenna offset – in this case – will define the position offset (x-y-z) relative the center of mass of the body, and yaw-pitch-roll of antenna will define the angular offset relative to x-y-z axes of the body frame.