\(\bar{R}\) and \(\kappa\) are two types of
concentration parameter that are commonly used in directional
data analysis. \(\kappa\) is one of the parameters of the
parametric von Mises distribution, which is difficult to
estimate from the data. \(\bar{R}\) is easier to calculate
from data. Rbar2kappa converts \(\bar{R}\) to
\(\bar{\kappa}\) using the following approximate empirical
formula:
\(\kappa =
\frac{\bar{R}(p+1-\bar{R}^2)}{1-\bar{R}^2}
\)
where \(p\) marks the number of parameters in the data space (1
for circle, 2 for a sphere).