[R] Natural colours for topographic data

[Barry Rowlingson]

On Tue, Nov 24, 2009 at 8:42 AM, Karl Ove Hufthammer <karl at huftis.org> wrote:
> On Mon, 23 Nov 2009 12:21:03 -0500 David Winsemius
> <dwinsemius at comcast.net> wrote:
>> > I would be happy with a simple one, that just mapped negative values
>> > to water colours and positive values to land colours.
>>
>> Searching with the strategy "color positive negative zero" in r-search
>> and limiting it to r-help replies,  I get this Jim Lemon reply using
>> (naturally) plotrix's color.scale:
>>
>> http://finzi.psych.upenn.edu/R/Rhelp02/archive/90837.html
>>
>> The application to your needs looks pretty immediate.
>
> Thanks for the suggestion, but the arguments that 'color.scale' takes
> (range of red, green and blue values) makes it not very useful for this
> purpose.
>

 Have you tried my colourscheme package? Its not on CRAN but you can
get it from here:

http://r-forge.r-project.org/projects/colourscheme/

And can be installed thus:
 > install.packages("colourschemes",repos="http://r-forge.r-project.org")

 [sorry about the inconsistency between 'colourscheme' and 'colourschemes'!]

Vignette via r-forge's source code browser:
http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/*checkout*/pkg/inst/doc/colourschemes.pdf?rev=19&root=colourscheme

 It defines various ways of mapping values to colours and using those
colours in plots. I use topographic-style colour schemes in the
examples, so this might be just what you want. The example in
?multiRamp is this:

# topological colour scheme - water, land, ice:
     tramp = multiRamp(rbind(c(-2000,0),c(0,1000),c(1000,9000)),
      list(c("black","blue"),c("green","brown"),c("gray70","gray70"))
      )

then:

 > tramp(-100)
 [1] "#0000F2FF"

 - is  a colour between black and blue in the ocean

> tramp(500)
 [1] "#539515FF"

 - is somewhere between green and brown in the land

 > tramp(1500)
 [1] "#B3B3B3FF"

 - is the gray of the ice.

No logarithmic colour scaling, but I do detail in the vignette how to
write your own colour scheme functions that are compatible with the
ones supplied. Will be glad to help more on this!

Barry