unwrapAngle.Rd

% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/misc.R
\name{unwrapAngle}
\alias{unwrapAngle}
\title{Unwrap an Angle That Suffers Modulo-360 Problems}
\usage{
unwrapAngle(angle)
}
\arguments{
\item{angle}{an angle (in degrees) that is thought be near 360 degrees, with
added noise}
}
\value{
A list with two estimates: \code{mean} is based on an arithmetic
mean, and \code{median} is based on the median. Both are mapped to the range
0 to 360.
}
\description{
This is mostly used for instrument heading angles, in cases where the
instrument is aligned nearly northward, so that small variations in heading
(e.g. due to mooring motion) can yield values that swing from small angles
to large angles, because of the modulo-360 cut point.
The method is to use the cosine and sine of the angle, to construct "x" and
"y" values on a unit circle, then to find means and medians of x and y
respectively, and finally to use \code{\link[=atan2]{atan2()}} to infer the angles.
}
\examples{
library(oce)
true <- 355
a <- true + rnorm(100, sd = 10)
a <- ifelse(a > 360, a - 360, a)
a2 <- unwrapAngle(a)
par(mar = c(3, 3, 5, 3))
hist(a, breaks = 360)
abline(v = a2$mean, col = "blue", lty = "dashed")
abline(v = true, col = "blue")
mtext("true (solid)\n estimate (dashed)", at = true, side = 3, col = "blue")
abline(v = mean(a), col = "red")
mtext("mean", at = mean(a), side = 3, col = "red")
}
\author{
Dan Kelley
}