A partial component of ddfilter, although works as a stand-alone function.
This function removes locations by a given threshold speed as described in Shimada et al. (2012).
ddfilter_speed(sdata, vmax = 8.9, method = 1)A data frame containing columns with the following headers: "id", "DateTime", "lat", "lon", "qi".
The function filters the input data by the unique "id".
"DateTime" is date & time in class POSIXct.
"lat" and "lon" are the latitude and longitude of each location in decimal degrees.
"qi" is the numerical quality index associated with each location fix where a greater number indicates a higher accuracy
(e.g. number of GPS satellites used for estimation).
A numeric value specifying a threshold of speed from a previous and/or to a subsequent fix.
Default is 8.9km/h.
If this value is unknown, it can be estimated from sdata using the function vmax.
An integer specifying how locations should be filtered with vmax. A location is removed if the speed from a previous and(1)/or(2) to a subsequent location exceeds vmax. Default is 1 (both way).
The input data is returned without locations identified by this filter. The following columns are added: "pTime", "sTime", "pDist", "sDist", "pSpeed", "sSpeed". "pTime" and "sTime" are hours from a previous and to a subsequent fix respectively. "pDist" and "sDist" are straight distances in kilometres from a previous and to a subsequent fix respectively. "pSpeed" and "sSpeed" are linear speed from a previous and to a subsequent fix respectively.
This function removes locations if the speed from a previous and/or to a subsequent location exceeds a given threshold speed.
If vmax is unknown, it can be estimated using the function vmax.
Shimada T, Jones R, Limpus C, Hamann M (2012) Improving data retention and home range estimates by data-driven screening. Marine Ecology Progress Series 457:171-180 doi:10.3354/meps09747