[R] Plot a sphere

[Derick Schoonbee]

Thanks for the reply. The results are exactly the same as what I'm getting.
Now I'm thinking in the lines of:

z1 <- outer(x, y, f)
z2 <- -outer(x, y, f)

So, I want to attach the two hemispheres. But then I need to figure out how 
append vectors z1 & z2 and then 'feed' this to persp..

hmm, I'll look into it.

Regards,
D.

From: Spencer Graves <spencer.graves at pdf.com>
To: Derick Schoonbee <schoonbee at hotmail.com>
CC: r-help at stat.math.ethz.ch
Subject: Re: [R] Plot a sphere
Date: Thu, 25 Dec 2003 17:38:01 -0800

      A hemisphere is relatively easy;  try the following:

      x <- seq(-1, 1, length=21)
      Z <- outer(x, x, function(x, y)sqrt(1-x^2-y^2))
      persp(x=x, y=x, z=Z)

      A contour plot is also relatively easy:

      image(x=x, y=x, z=Z)
      contour(x=x, y=x, z=Z, add=T)

      However, if you want an honest perspective plot of a sphere complete 
with the underside, etc., I know of nothing in R that could do that.  S-Plus 
has "perspp", which could be used.  However, that seems to be one of the few 
features available in S-Plus that is not currently available in R.

       hope this helps.      spencer graves

Derick Schoonbee wrote:

>Hi,
>
>I'm new to R (and math ;) Would somebody please be so kind as to direct me 
>in plotting a 3D sphere?
>
>I tried something in the lines of:
>####
>y <- x <- seq(-pi, pi, length=pi*10)
>f <- function(x,y)
>{
>     z <- sqrt(pi - x^2 - y^2)
>     #z[is.na(z)] <- 0
>     z
>}
>z <- outer(x, y, f)
>
>persp(x, y, z, theta = 120, phi = 30)
>####
>
>I've also tried: .... make.surface.grid(...) .. persp( as.surface( grid, z) 
>) ... with the same result: 'Incomplete' demi sphere and others..
>
>Any suggestions/solutions would be appreaciated.
>
>Regards,
>Derick
>
>PS:Merry X-mas ;)
>
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