Space-Time Analytics of Tracks for the Understanding of Patterns of Life - Space-Time Integration in Geography and GIScience - page 381

Furthermore, GPS locations carry spatial uncertainty. GPS technology at a survey
grade can obtain centimeter accuracy, but consumer grade GPS receivers may have
spatial uncertainty to tens of meters. Precise latitude and longitude readings of GPS
may be misleading in terms of location accuracy. Therefore, the use of Geohash
codes, instead of latitude-longitude readings, will better preserve the innate spatial
uncertainty in track analysis.
After resampling and converting coordinates to Geohash codes, track analysis
can compare locations at each time interval to determine if similar tracks were taken
on these days. Geohash codes condense two dimensional latitude-longitude pairs to
one text string, in which the distance comparison can be based on the length of
common codes and the distance represented by the differences of digits at the end
of the Geohash strings. Figure 20.11 a shows an example of an individual that was
Fig. 20.11 Comparison of tracks to determine space-time deviance: ( a ) comparing locations
across days at the same time to reveal changes in tracks; ( b ) comparing distances in adjacent
locations to reveal changes in travel speed. The vertical line graphs show space-time deviance in
locations between two tracks ( a ) or in adjacent locations on the same track ( b ) over the days of
interest (Day1, Day2, ::: Dayn)