RT User Manual
Revision: 190902
75
Advanced Tools section
This section contains several settings for Advanced users. By default, these settings are
not switched on so you should navigate through the various tabs to review the settings
that apply to your application.
Displace Output tab
The RT can displace or move its outputs to another location in the vehicle. This simulates
the RT being mounted at the new location, rather than at its actual location. This function
displaces all of the outputs (position, velocity, acceleration) to this new location.
To enable output displacement, click the checkbox and enter the offsets to the new location
in the vehicle. The offsets are measured from the RT in the vehicle co-ordinate frame.
Select the directions from the dropdown lists and input the distances.
Note that the noise in the acceleration outputs will be much higher when output
displacement is used. Typical installations in moving vehicles have angular vibrations of
about 2 rad/s²; this equates to 2 m/s² of additional vibration of a 1 m output displacement.
It will be necessary to filter the data if output displacement is used.
Acceleration filters tab
The RT is able to filter the linear acceleration and the angular acceleration before they are
output. These filters affect the outputs on the CAN bus. On the NCOM output the non-
filtered values are output together with the filter characteristics and the NCOM decoders
provided by OxTS will implement the chosen filter. The linear acceleration and the angular
acceleration can be configured separately.
Due to vibration the accelerations (both linear and angular) are noisy. In particular, angular
acceleration is normally filtered when it is used. The RT can filter the acceleration outputs
using a second order low-pass filter. The characteristics of the filter can be set and viewed
in the Acceleration Filters tab in the Advanced Tools section of NAVconfig.
Designing the right filter is always a compromise between the noise reduction and the filter
delay. To help choose the filter, the software will compute the maximum delay over the 0 to
5 Hz interval and the Noise Reduction Factor over the full bandwidth. The Noise Reduction
Factor is the ratio of the filtered noise compared to the unfiltered noise assuming the
vibration is white (i.e. same amplitude across the frequency spectrum). A graph showing the
delay with respect to frequency can also be plotted. The delay is the
additional
delay of the
filter and not the total delay of the acceleration output. The RT has other delays, like
calculation delay, too.
