IMCA Mini RadaScan, Owner'S Manual

Page: 23 / 33

IMCA M 229 19
11.2.1 Error Model
The error in a position fix obtained from a GPS receiver is said to be circular. The easting and
the northing have approximately the same accuracy, making the confidence region around a
point estimate circular.
With a range-bearing local position reference sensor that is not the case. When the range-
bearing measurement is interpreted as a position fix, the error in the radial direction may be
of quite a different size to the error in the tangential direction. Radial error is more or less
constant over a wide operating range. For a given bearing error, tangential position error is
proportional to the distance from the sensor to the responder.
To illustrate this, imagine that across the normal range of operating circumstances that the
typical range error is 0.25 m and that the typical bearing error is 2.5 mrad. At 50 m the
tangential position will be accurate to 0.125 m. At 200 m the tangential position will be accurate
to 0.5 m.
Figure 15 – Error mode
radial
tangential
100m
0.25m
radial
tangential
0.25m
50m
tangential
0.25m
200m
radial
radial
radial
tangential
tangential
tangential