is there a way to visualize 3D normal distributions?

On 2/2/2006 5:01 PM, Michael wrote:

shape3d only gives rigid sphere... not the free form ellipsoid that I
want...

? If you run the demo, you'll see ellipsoids...

You just need to work out the appropriate transform to apply to a sphere 
to get the ellipsoid you want.  I imagine something like this:

sphere <- ellipsoid3d(2,2,2, qmesh=TRUE)
ellipsoid <- translate3d(rotate3d(sphere, matrix=chol(S)), xbar, ybar, 
zbar)

shade3d(ellipsoid)

is what you want, where S is the covariance matrix, and xbar,ybar,zbar 
have the obvious meaning.  (rotate3d() is used with a matrix that isn't 
a rotation matrix; it may not be obvious that this is allowed, but it is.)

Duncan Murdoch

On 2/2/06, Ben Bolker <bolker at ufl.edu> wrote:

Duncan Murdoch <murdoch <at> stats.uwo.ca> writes:

On 2/2/2006 3:39 AM, Michael wrote:

Hi all,

How do I visualize a contour of a tri-variate normal distribution?

I just like to see the ellipsoid very much. I hope there is a easy way

or

existing method in R.

The misc3d package includes a function for 3d contour plots; that 
should
do what you want.

  is contour3d really necessary or could you just plot ellipsoids?
(library(rgl); demo(shapes3d)) -- still a little bit of figuring
to do, but this should get you most of the way there.

  Ben Bolker

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