R/Inside.Polygon.R

In John-R-Wallace/JRWToolBox: What the package does (short line)

Inside.Polygon <- function(pts, h = hull)
{
#
# Input:
#    pts -- (n x 2) matrix of test points
#      h -- ([k+1] x 2) matrix of (ordered) vertices,
#                 [with last row = first row]
# Output:
#     (n x 1) logical vector indicating inclusion of tests points
#           in the convex polygon formed by h
#
    n <- nrow(pts)
    k <- nrow(h) - 1
    if(!all(h[1,  ] == h[k + 1,  ])) {
        h <- rbind(h, h[1,  ])
        k <- k + 1
    }
#
# compute slopes and intercepts of boundary lines
#
    b <- diff(h[, 2])/diff(h[, 1])
    a <- diag(as.matrix(h[1:k, ]) %*% t(cbind( - b, 1)))    
#   compute centroid and its residuals from boundary lines
#
    m <- rep(1/k, k) %*% as.matrix(h[1:k,  ])
    r0 <- m[2] - (a + b * m[1])    #
#  compute residuals of test points from boundary lines
#
    r <- outer(pts[, 2], rep(1, k)) - outer(pts[, 1], b) - outer(rep(1, n), a)
    signs <- (r %*% diag(r0)) > 0
    ans <- as.vector(signs %*% rep(1, k) == k)
    ans
}