DEPONS2R (version 1.2.6)

interpolate.ais.data: Interpolate AIS data

Description

Interpolates ship movement tracks obtained from Automatic Identification System (AIS) data to obtain exactly one position per 30 minutes. The first and last position in the original track are omitted unless minutes = 0 or 30 and seconds = 0.

Usage

interpolate.ais.data(aisdata)

Value

Returns a data frame with the same columns as the input data. Tracks that are too short to interpolate are omitted (with a warning)

Arguments

aisdata

Data frame including the columns 'id' (ship identifier), 'time' (text string readable by as.POSIXct), 'x' and 'y' (recorded ship position, unit: meters), and potentially additional columns

See Also

read.DeponsShips and ais.to.DeponsShips

Examples

data(aisdata)
ais.testdata <- aisdata[c(12,14,16) ,]
plot(ais.testdata[c("x", "y")], asp=1, col="green", pch=16, xlim=c(780000, 837000))
lines(ais.testdata[c("x", "y")])
# Add 600 sec to 'time' to mis-allign with intervcal needed
ais.testdata$time <- format(as.POSIXlt(ais.testdata$time, tz = "UTC")+600)
text(ais.testdata[c("x", "y")]-900, ais.testdata$time, adj=0, cex=0.5)
interpolated <- interpolate.ais.data(ais.testdata)
points(interpolated[,c("x", "y")], col="red")
text(interpolated[c("x", "y")]-900, interpolated$time, adj=0, cex=0.5)
legend("bottomright", bty="n", pch=c(16, 1), col=c("green", "red"),
    legend=c("original positions", "interpolated"))