Rtk Gnss; The Sensor Co-Ordinate Frame; Roll, Pitch And Heading - Advanced Navigation Spatial FOG Reference Manual

5.5

RTK GNSS

RTK stands for real time kinematic. RTK is a technology used to significantly enhance
the accuracy of GNSS. With standard GNSS the accuracy achievable is approximately
2.5 metres, with RTK GNSS the accuracy achievable is 0.01 metres. RTK works by
estimating the phase of the carrier wave of the GNSS signal. By using the phase of the
carrier wave, rather than the data content, RTK is able to measure the signal 1000
times more precisely.
RTK GNSS requires continuous correction data from a base station to function. These
corrections are typically received either over a radio modem or through a cellular
network.
5.6

The Sensor Co-ordinate Frame

Inertial sensors have 3 diferent axes: X, Y and Z and these determine the directions
around which angles and accelerations are measured. It is very important to align the
axes correctly in installation otherwise the system won't work correctly. These axes are
marked on the top of the device as shown in Illustration 1 below with the X axis
pointing in the direction of the connector, the Z axis pointing down through the base of
the unit and the Y axis pointing out of the starboard side.
Illustration 1: Spatial FOG axes
When installed in an application the X axis should be aligned such that it points
forwards and the Z axis aligned so that it points down when level. A good way to
remember the sensor axes is the right hand rule, which is visualised in Illustration 2.
You take your right hand and extend your thumb, index and middle. Your thumb then
denotes the X axis, your index denotes the Y axis and your middle denotes the Z axis.
5.7

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
Spatial FOG Reference Manual
Page 16 of 144
Version 2.3
03/05/2018
Illustration 2: First right hand rule