speedfilter: Filter track data for speed
Description
Create a filter of a track for "bad" points implying a speed of motion
that is unrealistic.Usage
speedfilter(x, max.speed = NULL, test = FALSE, ...)
Arguments
max.speed
speed in kilometres per hour
test
cut the algorithm short and just return first pass
Value
- Logical vector matching positions in the coordinate records that pass the
filter.
Details
Using an algorithm (McConnnell et al, 1992), points are tested for
speed between previous / next and 2nd previous / next points.
Contiguous sections with an root mean square speed above a given
maximum have their highest rms point removed, then rms is
recalculated, until all points are below the maximum. By default
an (internal) root mean square function is used, this can be specified by the
user.
If the coordinates of the trip data are not projected, or NA the
distance calculation assumeds longlat and kilometres (great circle). For
projected coordinates the speed must match the units of the coordinate system.
(The PROJ.4 argument "units=km" is suggested).References
The algorithm comes from McConnell, B. J. and Chambers, C. and
Fedak, M. A. (1992) Foraging ecology of southern elephant seals in
relation to the bathymetry and productivity of the southern ocean.
_Antarctic Science_ *4* 393-398