The task of this stage is to filter errors (‘‘wild’’ points) in GPS
data that cannot be removed at the stage ‘‘Adaptive Kalman
Filtering.’’ This is realized on the basis of knowledge and expertise
for raw GPS data in the form of predefined rules.
Experiments show that the largest errors in GPS data were
when the following events occurred: transition from invalid to
valid GPS data, changes in the number of visible satellites,
transitions ‘‘movement-stop-movement,’’ walking with very low
speed (less than 3 km/h), which is typical for the blind, and when
static GPS navigation is active