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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 a given radius within target locations to reduce computation time.

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 = "log.txt"
)

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 (in metres) used for distance calculations. Defaults to EPSG:3035.

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

if (FALSE) { # \dontrun{
library(AISanalyze)
data("ais")
data("point_to_extract")

point_to_extract$timestamp <- as.numeric(lubridate::ymd_hm(datetime))

ais <- ais %>%
  dplyr::mutate(timestamp = as.numeric(lubridate::ymd_hms(datetime))) %>%
  AIStravel(ais_data = .)

# to interpolate all vessel locations separated by > 60 seconds
out <- AISinterpolate(ais_data = ais,
               type_interpolation = "maximum_gap_seconds",
               maximum_gap_seconds = 60,
               crs_meters = 3035)

# to interpolate all vessel locations at exact timestamps,
# within a radius of 200 000 meters around
# target locations
out <- AISinterpolate(ais_data = ais,
           type_interpolation = "exact_timestamp",
           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)
           } # }