pgirmess (version 2.0.2)

expandpoly: Homothetia (size expansion) of a polygon

Description

Compute the new coordinates of polygon expanded by a factor.

Usage

expandpoly(mypol, fact)

Value

A matrix of polygon coordinates

Arguments

mypol

matrix or data.frame of polygon coordinates

fact

expansion factor

Details

The polygon area obtained after expansion is equal to $fac{t}^2$ times the original polygon area

See Also

polygon

Examples

x<-c(-5,-4.5,0,10,5)
y<-c(-10,0,5,5,-8)
poly<-cbind(x,y)
plot(-10:20,-20:10,type="n")
polygon(poly)
polygon(expandpoly(poly,1.5),border="red")
polygon(expandpoly(poly,0.5),border="blue")