spanAngle <- function(x){
z <- x
if(!is.null(x$fingers)){
z$x <- x$fingers[,1]
z$y <- x$fingers[,2]
}
z$x <- z$x - x$center[1]
z$y <- z$y - x$center[2]
if(is.null(z$x)) return(0)
if(length(z$x) == 1) return(0)
theta <- atan2(z$y, z$x) + pi
if(length(z$x) == 2) return(as.numeric(abs(theta[2]-theta[1])))
theta <- sort(theta)
N <- length(theta)
d <- numeric(N)
d[1:(N-1)] <- diff(theta)
d[N] <- 2*pi - theta[N] + theta[1]
return(2*pi - max(d))
}
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