ais.to.DeponsShips {DEPONS2R}

Convert ship tracks to DeponsShips object

Description

Convert Automatic Identification System (AIS) data for ships to ship track objects. This is done by cropping one or more ship tracks to the extent of a landscape and converting the data to a DeponsShips-class object. If the AIS data does not include ship positions recorded in half-hour steps, the tracks are interpolated to make objects suitable for use in DEPONS.

Usage

ais.to.DeponsShips(data, landsc, title = "NA", ...)

Arguments

data

data.frame with ship positions and the times at which the positions were recorded. Must contain the columns 'id', 'time' (of the form " type, character), 'length' (ship length, meters), 'x', and 'y' (position, meters/UTM).

landsc

A DeponsRaster object corresponding to the landscape that the ships move in. It is assumed that the spatial projection of the ship positions corresponds to that of the DeponsRaster object

title

Title of the output object

...

Optional parameters, including 'startday' and 'endday' (" from 'data'. If startday = endday the output object will contain up to 49 positions from the selected date for each vessel track.

Value

Returns a DeponsShips object containing one or more ships assigned to each of the routes in the object. All ships on a particular route move at the same speed along the route. The routes are defined by x and y coordinates based on the same coordinate reference system as the landscape they are located in. The speed that ships use after reaching a particular position (a particular 'virtual buoy') is calculated from the distance to the following position, and the time it takes reaching that position. If speed is included in the input AIS data, this is NOT used. The routes include one position per half-hour time step, corresponding to the default time step used in the DEPONS model. If input data does not include one position per half hour, new positions are generated using linear interpolation. If the input data contains many positions in a particular half-hour interval, only the positions closest to the half-hour interval are used. The routes contain information about the number of half-hour intervals were ships 'pause' at a particular location, e.g. in a port. These are calculated based on the input AIS data.

See Also

aisdata for an example of data that can be used as input to ais.to.DeponsShips. The function builds on interpolate.ais.data, which interpolates tracks to ensure that there is a position every 30 minutes. See write.DeponsShips for conversion of DeponsShips objects to json-files to be used in DEPONS. Use routes, ships, and title for inspection/modification of the ship tracks.

Examples

data(aisdata)
plot(aisdata$x, aisdata$y, type="n", asp=1)
ids <- sort(unique(aisdata$id))
my.colors <- heat.colors(length(ids))
for (i in 1:length(ids)) {
  id <- ids[i]
  points(aisdata$x[aisdata$id==id], aisdata$y[aisdata$id==id],
     cex=0.6, col=my.colors[i])
}
data(bathymetry)
plot(bathymetry, add=TRUE)
depons.ais <- ais.to.DeponsShips(aisdata, bathymetry)
the.routes <- routes(depons.ais)
for (i in 1:length(ids)) {
points(the.routes[[i]]$x, the.routes[[i]]$y,
        cex=0.6, pch=16, col=my.colors[i])
}
depons.ais <- ais.to.DeponsShips(aisdata, bathymetry,
   startday="2015-12-20", endday="2015-12-20")
routes(depons.ais)
aisdata2 <- aisdata
aisdata2$time <- format(as.POSIXct(aisdata$time)+300)
depons.ais2 <- ais.to.DeponsShips(aisdata2, bathymetry,
                               startday="2015-12-20", endday="2015-12-21")
routes(depons.ais2)