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Draw axes of a 3D ellipsoid

Source: R/ellipse3d.axes.R
ellipse3d.axes.Rd

A function to draw the major axes of a 3D ellipsoid from a correlation, covariance or sums of squares and cross products matrix.

Usage

ellipse3d.axes(
  x,
  centre = c(0, 0, 0),
  center = centre,
  scale = c(1, 1, 1),
  level = 0.95,
  t = sqrt(qchisq(level, 3)),
  which = 1:3,
  labels = TRUE,
  label.ends = c(2, 4, 6),
  ...
)

Arguments

x

A square positive definite matrix at least 3x3 in size. It will be treated as the correlation or covariance of a multivariate normal distribution.

centre, center

The center of the ellipse

scale

If x is a correlation matrix, then the standard deviations of each parameter can be given in the scale parameter. This defaults to c(1, 1, 1), so no rescaling will be done.

level

The coverage level of a simultaneous region. The default is 0.95, for a 95% region. This is used to control the size of the ellipsoid.

t

The size of the ellipsoid may also be controlled by specifying the value of a t-statistic on its boundary, which defaults to the square root of a chi-square statistic for a given level on 3 degrees of freedom.

which

An integer vector to select which variables from the object will be plotted. The default is the first 3.

labels

Either a logical value, a character string, or a character vector of length 3. If TRUE, the default, the axes are labeled PC1, PC2, PC3. If a single character string, the digits 1, 2, 3 are pasted on the end.

label.ends

A vector of length 3 indicating which ends of the axes should be labeled, corresponding to a selection of rows of the 6 x 3 matrix of axes end points. Default: c(2,4,6).

...

Other arguments passed to segments3d and text3d.

Value

Returns a 6 x 3 matrix containing the end points of the three axis lines in pairs by rows.

See also

segments3d, text3d, ellipse3d

Author

Michael Friendly

Examples


data(iris)
iris3 <- iris[,1:3]
cov <- cov(iris3)
mu <- colMeans(iris3)
col <-c("blue", "green", "red")[iris$Species]

library(rgl)
#> Warning: package 'rgl' was built under R version 4.3.3
#> 
#> Attaching package: 'rgl'
#> The following objects are masked from 'package:heplots':
#> 
#>     arrow3d, bbox3d
plot3d(iris3, type="s", size=0.4, col=col, cex=2, box=FALSE, aspect="iso")
plot3d( ellipse3d(cov, centre=mu, level=0.68), col="gray", alpha=0.2,  add = TRUE)



axes <- ellipse3d.axes(cov, centre=mu, level=0.68, color="gray", lwd=2)