R Graphical Manual

Browse All

Last data update: 2014.03.03

R: Proximity Index

Prox	R Documentation

Proximity Index

Description

The function Prox simply computes the proportion of fixes that are proximal, based on some spatial threshold – dc (Bertrand et al. 1996). It also facilitates local-level proximity analysis

Usage

Prox(traj1, traj2, tc = 0, dc = 50, local = FALSE)

Arguments

`traj1`	an object of the class `ltraj` which contains the time-stamped movement fixes of the first object. Note this object must be a `type II ltraj` object. For more information on objects of this type see `help(ltraj)`.
`traj2`	same as `traj1`.
`tc`	time threshold for determining simultaneous fixes – see function: `GetSimultaneous`.
`dc`	distance tolerance limit (in appropriate units) for defining when two fixes are spatially together.
`local`	logical value indicating whether or not a dataframe, containing the distance between each simultaneous fix, should be returned.

Details

The function Prox can be used to test for the presence of attraction (via proximity) in wildlife telemetry data. Prox is simply the proportion of simultaneous fixes within the threshold distance – dc. The local output (dataframe) can be useful for examining variation in proximity through time.

Value

If local=FALSE (the default) Prox returns the numeric value of the Prox index. If local=TRUE Prox returns a dataframe (containing the date/times of all simultaneous fixes, along with the distance between fixes at each time.

References

Bertrand, M.R., DeNicola, A.J., Beissinger, S.R, Swihart, R.K. (1996) Effects of parturition on home ranges and social affiliations of female white-tailed deer. Journal of Wildlife Management, 60: 899-909.

Examples

data(deer)
deer37 <- deer[1]
deer38 <- deer[2]
#tc = 7.5 minutes, dc = 50 meters
Prox(deer37, deer38, tc=7.5*60, dc=50)
df <- Prox(deer37, deer38, tc=7.5*60, dc=50, local=TRUE)