IsoplotR (version 6.5)

ellipse: Get error ellipse coordinates for plotting

Description

Constructs an error ellipse at a given confidence level from its centre and covariance matrix

Usage

ellipse(x, y, covmat, alpha = 0.05, n = 50)

Value

an [nx2] matrix of plot coordinates

Arguments

x

x-coordinate (scalar) for the centre of the ellipse

y

y-coordinate (scalar) for the centre of the ellipse

covmat

the [2x2] covariance matrix of the x-y coordinates

alpha

the probability cutoff for the error ellipses

n

the resolution (number of segments) of the error ellipses

Examples

x = 99; y = 101;
covmat <- matrix(c(1,0.9,0.9,1),nrow=2)
ell <- ellipse(x,y,covmat)
plot(c(90,110),c(90,110),type='l')
polygon(ell,col=rgb(0,1,0,0.5))
points(x,y,pch=21,bg='black')