lab5.R

# Create the S4 Class Trajectory
setClass("Trajectory", representation(x = "numeric", y = "numeric", time = "numeric"))

#make a new object with class Trajectory
colin <- new("Trajectory", x = 21.5, y = 21.5, time = 1200)

# create the S4 Class TrajectoryExtra which includes the Trajectory class
setClass("TrajectoryExtra", representation(speed = "numeric", direction = "numeric"), contains = "Trajectory")

colin1 <- new("Trajectory", x = c(0:10), y = c(20:30), time = c(1200:1210))

# define a coercion method (setAs) that coerces from Trajectory to TrajectoryExtra, and which
# computes the speed and direction fields from speed and direction fields from x/y/t

setAs ("Trajectory", "TrajectoryExtra",
function (from , to) {

#calculate the speed, first we calculate the magnitude and then we divide this by time to get speed
dist = sqrt(from@x^2 + from@y^2)
s = dist / from@time

#to find the direction we know that the we can use arc tangent to get this. atan(y/x). We need the answer in degrees as R works in radians.
direct = atan(from@y/from@x)*(180/pi)


new("TrajectoryExtra", x = from@x, y = from@y, time = from@time, speed = s, direction = direct)

	}
)

# Test the method	
as(colin1, "TrajectoryExtra")