persp & colors

Timur is this what you are looking for?

from Rtips at

http://lark.cc.ukans.edu/~pauljohn/R/statsRus.html#5.42

---------------------------------- Question: is it
possible to shade the 3d surface like a contour plot?
i.e. black for large z, white for small z, say 

Answer: 

# Create a simple surface f(x,y) = x^2 - y^2 

        nx <- 21
        ny <- 21
        x <- seq(-1, 1, length = nx)
        y <- seq(-1, 1, length = ny)
        z <- outer(x, y, function(x,y) x^2 - y^2)

        #  Average the values at the corner of each
facet
        #  and scale to a value in [0, 1].  We will
use this
        #  to select a gray for colouring the facet.

        hgt <- 0.25 * (z[-nx,-ny] + z[-1,-ny] +
z[-nx,-1] + z[-1,-1])
        hgt <- (hgt - min(hgt))/ (max(hgt) - min(hgt))

        #  Plot the surface with the specified facet
colours.

        persp(x, y, z, col = gray(1 - hgt), theta =
35)
        persp(x, y, z, col = cm.colors(10)[floor(9 *
hgt + 1)], theta = 35)

(from Ross Ihaka) 

Regards,
Michael Grant

On Sun, Jun 01, 2003 at 06:53:55PM +0200, Uwe Ligges
wrote:

but I'd like to persp()' colors behave like in

image() function!

That's not easy, because you have to redefine x, y

and z values.

Simple example:

 x <- y <- 1:2
 z <- matrix(1:4, 2)
 image(x, y, z)    # OK, quite nice

but

 persp(x, y, z)

has only one facet. So the only way is to

calculate the 9 values for x, 

y, and z to get the corners for the 4 facets in

it.

That's easy for x and y, but can be impossible for

z...

OK, thank you for answer!
But, I saw that other mathematic frameworks (CERN
ROOT for instance)
can plot 3D surfaces with colors corresponding to
z-value.
Is there way to do this in R (with another
functions/packages)?
It's not necessary to use _one_ color per facet,
yes?.. :)


--
WBR,
Timur.

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