Figure 78: First Right-hand Rule
You take your right hand and extend your thumb, index and middle. Your thumb then denotes the positive X
axis, your index denotes the positive Y axis and your middle denotes the positive Z axis.
12.3 The Body Co-ordinate Frame
Also known as the vehicle co-ordinate (reference) frame, this can be described most easily using a car (the
body or vehicle) as an example. The forward direction of travel for a car is the positive X axis, out to the right of
the car is the positive Y axis, and down is the positive Z axis. The distinction between the sensor co-ordinate
frame and the body co-ordinate frame becomes important when the INS device is not mounted with its axes
aligned to the vehicle axes, for example when the INS is mounted with a 90 degree heading rotation. Offset
measurements, which are described later in this document, will always be in the body co-ordinate frame to
remove any INS alignment variations. Generally any data output by the INS using the X, Y and Z axes will be
using the body co-ordinate frame.
12.4 Roll, Pitch and Heading
Orientation can be described by the three angles roll, pitch and heading: these are known as the Euler angles.
The rotation axes of roll, pitch and heading are shown visually in
. The arrow indicates
the positive rotation direction.
Roll is the angle around the X axis and is zero when the unit is level. Pitch is the angle around the Y axis and is
zero when the unit is level. Heading is the angle around the Z axis and is zero when the positive X axis is
pointing to true north.
12.4.1 Second Right Hand Rule
The two right hand rules are often the best way to memorise the sensor axes and directions of positive rotation.
The first right hand rule gives the positive axis directions and is described in
. The second right hand rule shown in the figure below provides the direction of positive rotation. To use
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11 Oct 2022
Boreas Reference Manual • Boreas Reference Information
