Correct GPS errors in AIS tracks — AIScorrect

Detects and corrects GPS errors and delayed AIS messages that generate unrealistic vessel speeds, travelled distances, and travel times.

Usage

AIScorrect_speed(
  ais_data,
  crs_meters = 3035,
  threshold_speed_to_correct = 100,
  threshold_speed_to_correct_expr = function(speed_kmh) {
     return(15 +
    stats::median(speed_kmh[speed_kmh > 1], na.rm = T) + 5 *
    stats::sd(speed_kmh[speed_kmh > 1 & speed_kmh < stats::quantile(speed_kmh[speed_kmh >
    1], 0.75)]))
 },
  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. Another vessel identifier may be used if the column is named mmsi.
crs_meters: CRS (metres) used to calculate travelled distances. Defaults to EPSG:3035.
threshold_speed_to_correct: Speed threshold (km/h) above which observations are corrected.
threshold_speed_to_correct_expr: Function returning a vessel-specific speed threshold from speed_kmh.
nb_cores: Number of CPU cores used.
outfile: File used to save logs.

Value

The input data with corrected travel metrics and the following columns:

speed_kmh_corrected: Whether the speed was corrected.
time_travelled: Travel time (s).
distance_travelled: Travelled distance (m).
speed_kmh: Vessel speed (km/h).

Examples

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

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

out <- AIScorrect_speed(ais_data = ais,
                 crs_meters = 3035,
                 threshold_speed_to_correct = 100)} # }