R help - Sep 2008 - how to draw the legend about color from 3d picture

I have drawed a picture with persp, it's 3d map with different color,
indicate different altitude. In gnuplot, the corresponding command
'splot' will generate a picture beside to indicate the relationship
between color and altitude. But in R, how to draw it? I have read the
manual of legend, but they are all about how to draw a legend with
colored text, not a continuous varing color with corresponding number.

On 9/5/2008 8:06 AM, yk wrote:
> I have drawed a picture with persp, it's 3d map with different color,
> indicate different altitude. In gnuplot, the corresponding command
> 'splot' will generate a picture beside to indicate the relationship
> between color and altitude. But in R, how to draw it? I have read the
> manual of legend, but they are all about how to draw a legend with
> colored text, not a continuous varing color with corresponding number.
I don't think there's an automatic way to do this (though probably some 
package provides one).

If you want to write your own, take a look at example(filled.contour). 
The legend it draws is done by this code:

     plot.new()
     plot.window(xlim = c(0, 1), ylim = range(levels), xaxs = "i",
         yaxs = "i")
     rect(0, levels[-length(levels)], 1, levels[-1], col = col)
     if (missing(key.axes)) {
         if (axes)
             axis(4)
     }
     else key.axes
     box()

(but it has done a lot of setup using layout() and par() before this).

Duncan Murdoch

Look at the color.legend function in the plotrix package to see if it does what
you want.  You may want to use the layout function to split the graphics device
into 2 sections, one for the persp plot and the other to hold the legend.

Hope this helps,

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
(801) 408-8111


> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of yk
> Sent: Friday, September 05, 2008 6:07 AM
> To: r-help at r-project.org
> Subject: [R] how to draw the legend about color from 3d picture
>
> I have drawed a picture with persp, it's 3d map with
> different color, indicate different altitude. In gnuplot, the
> corresponding command 'splot' will generate a picture beside
> to indicate the relationship between color and altitude. But
> in R, how to draw it? I have read the manual of legend, but
> they are all about how to draw a legend with colored text,
> not a continuous varing color with corresponding number.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

It may not help the original poster, but here's a solution based on what
Greg
said above:

# Load plotrix
library(plotrix)

# Create a new layout to divide the graphics in 2, the first one (displaying
the persp() graph) being 4 times larger than the second one (displying the
legend)

layout(matrix(c(1,2),1,2,byrow=T),widths=c(4,1))

# Setup the color palette, here for exemple a 20-step heatmap from white
through yellow to red colors
grey.colors <- colorRampPalette( c("white", "yellow",
"black") )
color <- grey.colors(20)

# Run the persp() command with right definition of facets and colors
zfacet <- z[-1,-1] + z[-1,-ncol(z)] + z[-nrow(z),-1] + z[-nrow(z),-ncol(z)]
persp(x, y, z, col=color[cut(zfacet, nbcol)], theta=...)

# Stetup and display the legend, 
col.labels <-
c("0.0","0.2","0.4","0.6","0.8","1.0")
# For z values between
0 and 1
plot(0:10,type="n",axes=FALSE,xlab="",ylab="") #
Blank plot required for the
legend to be added to
color.legend(1,1.5,9,8,col.labels,color,gradient="y",align="rb")

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