# ellipse3d.axes: Draw axes of a 3D ellipsoid In heplots: Visualizing Hypothesis Tests in Multivariate Linear Models

## Description

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

## Usage

 ```1 2 3``` ```ellipse3d.axes(x, centre = c(0, 0, 0), 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` 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 confidence level of a simultaneous confidence 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` This parameter selects 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.

## Author(s)

Michael Friendly

`segments3d`, `text3d`, `ellipse3d`

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11``` ```data(iris) iris3 <- iris[,1:3] cov <- cov(iris3) mu <- colMeans(iris3) col <-c("blue", "green", "red")[iris\$Species] library(rgl) 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) ```

### Example output

```Loading required package: car

Attaching package: ‘rgl’

The following object is masked from ‘package:heplots’:

arrow3d

Warning messages:
1: In rgl.init(initValue, onlyNULL) : RGL: unable to open X11 display
2: 'rgl.init' failed, running with 'rgl.useNULL = TRUE'.
```

heplots documentation built on Oct. 7, 2021, 1:07 a.m.