geometry (version 0.5.0)

polyarea: Determines area of a polygon by triangle method.

Description

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.

Usage

polyarea(x, y, d = 1)

Value

Area(s) of polygon(s).

Arguments

x

X coordinates of vertices.

y

Y coordinates of vertices.

d

Dimension of array to work along.

Author

David Sterratt based on the octave sources by David M. Doolin

Details

If the optional dim argument is given, then polyarea works along this dimension of the arrays x and y.

Examples

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)