Function to estimate the maximum linear speed between two consecutive locations.
vmax(sdata, qi = 5, prob = 0.99, ...)A data frame containing columns with the following headers: "id", "DateTime", "lat", "lon", "qi".
See the data turtle for an example.
The function filters the input data by a unique "id" (e.g. transmitter number, identifier for each animal).
"DateTime" is the GMT date & time of each location in class POSIXct
or character with the following format "2012-06-03 01:33:46".
"lat" and "lon" are the latitude and longitude of each location in decimal degrees.
"qi" is the quality index associated with each location fix.
The input values can be either the number of GPS satellites or Argos Location Classes.
Argos Location Classes will be converted to numerical values, where "A", "B", "Z" will be replaced with "-1", "-2", "-3" respectively.
The greater number indicates a higher accuracy.
An integer specifying the lowest quality index of a location that is qualified to be used in the estimation. Default is 5 (e.g. 5 GPS satellite or more).
A numeric value to specify a sample quantile. Default is 0.99.
Extra arguments passed to dupfilter.
Maximum linear speed (vmax) estimated from the input data. The unit is km/h.
The function first calculates the linear speed between each pair of two consecutive locations. It then discards extreme values, based on the specified quantile, to exclude potential outliers from the estimation process. The maximum value in the retained dataset (i.e. without outliers) represents the maximum linear speed at which an animal would travel between two consecutive locations.
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