ellipsoid {gellipsoid}

Calculate an ellipsoid in 3D

Description

Calculates a qmesh3d object representing a 3D ellipsoid with given center and shape matrix. The function allows for degenerate ellipsoids where the shape matrix has rank < 3 and plots as an ellipse or a line.

Usage

ellipsoid(center, shape, radius = 1, segments = 60, warn.rank = FALSE)

Arguments

center

A vector of length 3 giving the center of the 3D ellipsoid, typically the mean vector of a data matrix.

shape

A 3 x 3 matrix giving the shape of the 3D ellipsoid, typical a covariance matrix of a data matrix.

radius

radius of the ellipsoid, with default radius=1, giving a standard ellipsoid. For a multivariate sample with dfe degrees of freedom associated with shape, an ellipsoid of level coverage can be calculated using radius=sqrt(3 * qf(level, 3, dfe)).

segments

number of line segments to use in each direction in the wire-frame representation of the ellipsoid

warn.rank

warn if the shape matrix is of rank < 3?

Details

The ellipsoid is calculated by transforming a unit sphere by the Cholesky square root of the shape matrix, and translating to the center.

The ellipsoid can be plotted with plot3d

Value

A qmesh3d object

Author(s)

Michael Friendly and John Fox, extending Duncan Murdoch

Examples

## none yet