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Interpolate AIS positions

Source: R/AISinterpolate.R
AISinterpolate.Rd

Interpolates vessel positions either: (depending on type_interpolation)

  • to ensure time intervals do not exceed a specified maximum (= maximum_gap_seconds).

  • at user-defined timestamps (= exact_timestamp). Interpolation can optionally be restricted to specific regions to reduce computation time with locations_of_interest and radius arguments.

Usage

AISinterpolate(
  ais_data,
  type_interpolation,
  maximum_gap_seconds,
  exact_timestamp = list(timestamp_to_interpolate, locations_of_interest, radius),
  crs_meters = 3035,
  nb_cores = 1,
  outfile = tempfile()
)

Arguments

ais_data

AIS data frame containing timestamp, lon, lat, and mmsi. timestamp must be Unix time (seconds since 1970-01-01), while lon and lat must be numeric.

type_interpolation

Interpolation mode: "maximum_gap_seconds" or "exact_timestamp".

maximum_gap_seconds

used when type_interpolation = "maximum_gap_seconds": threshold above which AIS signals are interpolated.

exact_timestamp

List used when type_interpolation = "exact_timestamp", containing:

  • timestamp_to_interpolate

  • locations_of_interest: (optional) data frame with lon and lat columns corresponding to each timestamp_to_interpolate

  • radius: (optional) a search radius (m) around target locations

crs_meters

CRS (metres) used to calculate distances in the study area (defaults to EPSG:3035, Europe). Tip: use suggest_crs function (crsuggest package) to find a suitable CRS for your study area.

nb_cores

Number of CPU cores used.

outfile

File used to save logs.

Value

The interpolated AIS data with an additional column:

  • interpolated: Whether the position was interpolated.

Examples

data("ais")
data("point_to_extract")

# use only a sample for the example:
ais <- ais[20000:30000, ]

# Define the Unix time (seconds since 1970-01-01)
point_to_extract$timestamp <- as.numeric(lubridate::ymd_hm(point_to_extract$datetime))
ais$timestamp <- as.numeric(lubridate::ymd_hms(ais$datetime))

# calculate the travelled distance, time, and speed:
ais <- AIStravel(ais_data = ais, crs_meters = 3035)

# Interpolate all AIS signals further than > 120 seconds:
out <- AISinterpolate(ais_data = ais,
                      type_interpolation = "maximum_gap_seconds",
                      maximum_gap_seconds = 120, ## Alternatively, you can
                      ## interpolate at target timestamps with:
                      # exact_timestamp = list(
                      #      timestamp_to_interpolate = point_to_extract$timestamp,
                      #      locations_of_interest = data.frame(lon = point_to_extract$lon,
                      #                                         lat = point_to_extract$lat),
                      #      radius = 200000),
                      crs_meters = 3035)