Re: [R] is there a way to visualize 3D normal distributions?

From: Ben Bolker <bolker_at_zoo.ufl.edu>
Date: Fri 03 Feb 2006 - 09:55:47 EST

Michael wrote:
> shape3d only gives rigid sphere... not the free form ellipsoid that I
> want...
>

   one or the other of us is missing something.

    after running demo(shapes3d)
[to define ellipsoid3d] and rgl.clear(),

s1 <- ellipsoid3d(qmesh = TRUE, trans = diag(4)) shade3d(rotate3d(scale3d(s1, 1, 1, 2),

                  angle=pi/4, x=0, y=1, z=0),
         col = "red")

axis3d()

  produces an ellipsoid with radii (1,1,2) rotated by pi/4 around the y axis. I'm too lazy to figure out how to translate a variance-covariance matrix into a scaling/rotation matrix (the scale will want to be something like eigen(v)$values*qnorm(0.975) for a 95% contour, the rotation matrix is some function of the eigenvectors), but it seems to me that this will produce any ("free form"?) ellipsoid you want.

   cheers
     Ben Bolker



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