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window will change depending on the settings you choose, to help visualise the position
of the RT in relation the wheel speed.
Ideally the measurements would be made to an accuracy of 10 cm. Using higher precision
for the measurement does not improve the results. Using an accuracy figure worse than
20 cm will increase the drift of the RT. The accuracy can be specified as the same for all
measurements using Overall accuracy or it can be specified for each individual
measurement by clicking the Specify each accuracy separately checkbox. In either
case, choose a predefined value from the drop-down list or type in a value.
Enter the pulses per metre of the wheel speed. A value that is accurate to 10% is sufficient
unless you know the figure more accurately. The RT will improve this scaling factor
itself when GNSS is available. The Get improved settings utility (see page 59 for
details) can be used to apply a more accurate value calculated by the RT from a
calibration run. If this option is used then the RT should be allowed to recalibrate the
scaling value occasionally to account for tyre wear.
The wheel speed corrections will not be as effective in reducing the drift of the RT if the
wheel speed is measuring two wheels (i.e. after a differential), since the actual position
of the wheel is required for accurate navigation. If a post-differential encoder must be
used then the accuracy cannot be guaranteed.
For best results, a front wheel drive vehicle should be used with the wheel speed on a
rear wheel. The wheel speed pulses from driven wheels are less accurate.
Local co-ordinates
Adjustment: click … button to open properties window.
The RT can output the displacement from an origin in a local co-ordinate grid. To use
this option a “zero” location or origin must be chosen; the latitude, longitude and altitude
for the origin must be entered in to the RT. If an RT-Base S is available, then these will
be shown on the LCD. A rotation can also be specified to rotate the xy directions.
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