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.
Warning
This algorithm is not considered to be particularly relevant to the problems
involved with location uncertainty in animal tracking. It is provided
merely as an illustrative benchmark for further work. It is possible for the filter to become stuck in an infinite loop, depending
on the function passed to the filter. Several minutes is probably too long
for hundreds of points, test on smaller sections if unsure.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