User's Manual

InterSense Doc. No. 072-00105-0I07 Rev. 4.2
IS-900 User Guide Page 36 of 177
3.1. InterSense Coordinate Reference Frame
Before setting up the IS-900, it is important to review the standard InterSense coordinate
reference system. As a 6-DOF tracker, use of the “InterSense Coordinate Reference Frame”
throughout this manual helps explain the installation, calibration and tracking performance.
Figure 16 - InterSense Coordinate Reference Frame
Figure 16 shows the standard reference frame for both position and orientation of all InterSense
tracker systems.
The reference frame (hereafter referred to as Navigation frame or Nav frame or N frame) is the
locally-level geographic frame with its x-axis pointing north, y-axis east, and z-axis down.
It is important to understand that when setting up any InterSense system, the z-axis of the
tracking system’s coordinates must always point in the direction of gravity, whereas the x
and y axes may be set to any direction rotated about the z-axis.
Subsequent coordinate transformations by application software to change the direction of the z-
axis are normal, but the underlying reference of InterSense’s inertial components to gravity must
be maintained by the tracking system. The Euler angles reported by the tracker are described as
a sequence of rotations applied to the tracking device starting with its body axes initially aligned
with the Nav frame axes and resulting in the current orientation. The sequence starts with a
rotation by (+yaw) about the Z axis, followed by a rotation by (+pitch) about the new Y axis (i.e.
body frame axis), followed by a rotation by (+roll) about the new X axis (i.e. body frame x axis).
Yaw
Roll
Pitch
X
Y
Z