Thins out the 'bursts' in a GPS dataset

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Description

Thin out closely-timed bursts of locations

Usage

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lxy.thin.bursts(lxy, id = NULL, thresh = NULL, replace = c("mean",
  "median")[2], info.only = FALSE, dt.int.round.to = 0.1,
  tau.diff.max = 0.02, status = TRUE)

Arguments

lxy

A LoCoH-xy object

id

The id value(s) to be thinned

thresh

The threshhold for delta.t below which a pair of points is considered to be part of a burst, expressed either as a proportion of the median sampling frequency (0..1) or an absolute unit of time (in seconds)

replace

The burst replacement method ('mean' or 'median')

info.only

Show information about number of bursts (only)

dt.int.round.to

The proportion of the median sampling frequency that time intervals will be rounded to when computing the frequency table of sampling intervals (no change is made to the time stamps)

tau.diff.max

The maximum deviation from tau (the median delta.t of the entire dataset), expressed as a proportion of tau, that time difference between two points must fall for the distance between those two points to be included in the calculation of the median step length

status

Show status messages. T/F

Value

a LoCoH-xy object

Note

Many GPS devices have a feature to save 'bursts' of points close together in time (relative to the dominant sampling frequency) The 'burst' feature should not be confused with point averaging, whereby a GPS device internally averages locations for a period of time (e.g., 2 minutes) but saves a single location.

This function can be used to thin out 'bursts' of locations, when they are an artifact of data collection and therefore not desirable. Each group of points in a burst is replaced with a single point.

thresh is a numeric value for identifying which points should be considered part of a burst. When thresh < 1, it is taken to be a proportion of the median sampling frequency (0..1), and any pair of points that are recorded closer in time are considered part of a 'burst', When thresh > 1, it is taken to be absolute unit of time (in seconds).

To identify whether there are bursts in a LoCoH-xy dataset, and the sampling frequency of those bursts (i.e., the value

The two replacement methods are /codereplace="mean", in which case a burst of locations is replaced by a single point consisting of the spatial and temporal average of the burst, or /codereplace="median" in which case a burst of locations is replaced by the location at the temporal median of the burst. If /codereplace="mean", then any ancillary variables for the 'new' points will be set to NA.

Because this function deletes points, the nearest neighbor lookup table of the LoCoH-xy object (if any) will be deleted, and the parameters for random walk model will be recomputed.

See Also

lxy.plot.freq, lxy.thin.byfreq

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