Determines area of a polygon by triangle method. The variables
`x`

and `y`

define the vertex pairs, and must therefore
have the same shape. They can be either vectors or arrays. If
they are arrays then the columns of `x`

and `y`

are
treated separately and an area returned for each.

`polyarea(x, y, d = 1)`

x

X coordinates of verticies.

y

Y coordinates of verticies.

d

Dimension of array to work along.

Area(s) of polygon(s).

If the optional `dim`

argument is given, then `polyarea`

works along this dimension of the arrays `x`

and `y`

.

# NOT RUN { x <- c(1, 1, 3, 3, 1) y <- c(1, 3, 3, 1, 1) polyarea(x, y) polyarea(cbind(x, x), cbind(y, y)) ## c(4, 4) polyarea(cbind(x, x), cbind(y,y), 1) ## c(4, 4) polyarea(rbind(x, x), rbind(y,y), 2) ## c(4, 4) # }