expandpoly: Homothetia (size expansion) of a polygon

In pgirmess: Spatial Analysis and Data Mining for Field Ecologists

Homothetia (size expansion) of a polygon

Description

Compute the new coordinates of polygon expanded by a factor.

Usage

expandpoly(mypol, fact)

Arguments

mypol	matrix or data.frame of polygon coordinates
fact	expansion factor

Details

The polygon area obtained after expansion is equal to fact^2 times the original polygon area

Value

A matrix of polygon coordinates

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")

pgirmess documentation built on May 29, 2024, 4:26 a.m.