BayesX (version 0.3-3)

.ringDirxy: Compute direction of points in a polygon.

Description

This is (private, not exported) R code replacing the call to maptools:::.ringDirxy, which links to C code.

Usage

.ringDirxy(xy)

Value

Returns the integer -1 if the direction is counter-clockwise and 1 if the direction is clockwise.

Arguments

xy

a two-column matrix with x and y coordinates of at least 3 points which form a polygon

Author

Daniel Sabanes Bove

Examples

if (FALSE) ## Create test polygon ordered clockwise.
nPoints <- 200
sequence <- seq(1, 10, length = nPoints)
firstHalf <- sequence[1:(nPoints/2)]

test <- cbind(
  "x" = c(sequence, rev(sequence)),
  "y" = c(firstHalf, rev(firstHalf), -firstHalf, -rev(firstHalf))
)

plot(test, type="n")
polygon(test)

## Compute direction with this and the original function,
BayesX:::.ringDirxy(test)