downsampleXYZ: Downsample high-resolution GPS data

In andresgmejiar/lbmech: A Package to Study the Mechanics of Landscape and Behavior

Downsample high-resolution GPS data

Description

Downsample high-resolution *(x,y,t)* or *(x,y,z,t)* data to match a minimum spatial resolution.

Usage

downsampleXYZ(
  data,
  t_step,
  t_cut = t_step * 10,
  x = "x",
  y = "y",
  z = NULL,
  t = "t",
  ID = "ID"
)

Arguments

data	A data.frame or something coercible to a data.table containing all observations
t_step	The smallest allowable median time interval between observations. Any track with a median value below this will be resampled to a track of equally-spaced observations with time difference t_step. This should be selected based on the parameters that will be used to generate a world object such that each successive step is likely to fall outside of the range of possible raster transitions. For example, for a given source dem in makeGrid, a given distances = 16 in makeWorld (implying that contiguity = 2), and an estimated animal maximum velocity of v_max = 1.5 m/s, t_step should be at least t_step = res(dem) / v_max * (contiguity + 1) * sqrt(2)
t_cut	A numeric. Any gap exceeding this value in seconds in a given track will be treated as the start of a new segment. Default is t_step * 10.
x	A character string representing the data column containing the 'x' coordinates in any projection.
y	A character string representing the data column containing the 'y' coordinates in any projection.
z	Optional. A character string representing the data column containing the 'z' elevations.
t	A character string representing the data column containing the time values, either as a numeric of successive seconds or as a date time string
ID	A character string representing the data column containing the unique ID for each observed trajectory. In other words, each set of points for each continuous observation for each observed individual would merit a unique id.

Value

A data.table, containing the original input data but with all overly-high resolution tracks downsampled to an acceptable rate of observations and column names prepared for the getVelocity function.

Examples

# Generate fake data with x,y coordinates, z elevation, and a t
# column representing the number of seconds into the observation
data <- data.table(x = runif(10000,10000,20000),
                   y = runif(10000,30000,40000),
                   z = runif(10000,0,200),
                   t = 1:1000,
                   ID = rep(1:10,each=1000))
                   
# Set the minimum value at 3 seconds
data <- downsampleXYZ(data = data, t_step = 3, z = 'z')

andresgmejiar/lbmech documentation built on Feb. 2, 2025, 12:37 a.m.