Smoothing directional (angular) data in R

Question

I'm trying to deal with some motion analysis software tracking errors after the data is exported. For some frames the direction is rotated by 180 degrees from the "true" direction.

I would like to smooth the data set so that when the direction changes by ~180 in a single frame, it is transformed to reflect the actual angle.

Is anyone aware of a way to solve this using any of the circular statistics packages in R language such as CircStats? Alternatively, I could imagine a script that checks if frame to frame variation is near 180 degrees, subtracts 180 if this is true, then moves to the next frame. Does this sound like a reasonable approach and would it be easily implemented in R?

I'm afraid I don't have the rep to upload a figure describing the problem (it's very easy to see), but here is a example dataset.

Thanks for the help. I've been a longtime user of stack overflow but have never failed to find my answer before needing to ask before.

David

edit - attached image

Answer 1

It was an interesting problem to solve! It needs to be iterative since whenever a value is changed, it can solve a problem but create another... Let me know if it does the trick.

threshold <- 90
correction <- 180

dat <- read.table("angle_data.txt", header=TRUE)
dat <- ts(dat)

repeat {
    diffs <- dat - lag(dat, k = 1)
    probl <- which(abs(diffs[,2]) > threshold)

    if(length(probl)==0)
        break

    obs.1 <- dat[probl[1], 2]
    obs.2 <- dat[probl[1] + 1, 2]

    dat[probl[1] + 1, 2] <- obs.2 + sign(obs.1 - obs.2) * 180
}