R help - Nov 2009 - Natural colours for topographic data

Dear list members

I'm currently working on some topographic (elevation) data, and was 
somewhat surprised that the 'topo.colors' and 'terrain.colors'
are of
little to no use here.

The problem is that these functions only return a palette of colours; 
they don't map depth values to colours. So if I plot (using 'image',
'persp' or similar functions) and specify these palettes, ocean areas 
may coloured green (indicating) land, which may be quite confusing.

I have looked through various packages, and have found several colour 
palette functions, but none that do what I need.

Basically, I just need a function that takes a vector of elevation 
values as input, and outputs a vector of 'natural' colours. For negative
values (i.e., ocean), the 'blue' colours of 'topo.colors' would
be OK,
and for positive values either the colours of 'terrain.colors' or the 
non-blue colours of 'topo.colors' would look nice.

It is of course not very difficult to create such a function myself, 
e.g. using the 'cut' function and a standard palette. But perhaps 
somebody has already has made one?

My ideal topographic colour mapping function would support separate 
colour levels for water and land (so that you can specifiy for example 5 
colours of water, from a depth of 5000 meters to 0 meters, and 20 
colours of land, from a depth of 0 meters to 2000 meters), support 
several nice palettes, and also support logarithmic colour mapping. But 
I would be happy with a simple one, that just mapped negative values to 
water colours and positive values to land colours.

-- 
Karl Ove Hufthammer

On Nov 23, 2009, at 11:52 AM, Karl Ove Hufthammer wrote:
> Dear list members
>
> I'm currently working on some topographic (elevation) data, and was
> somewhat surprised that the 'topo.colors' and
'terrain.colors' are of
> little to no use here.
>
> The problem is that these functions only return a palette of colours;
> they don't map depth values to colours. So if I plot (using
'image',
> 'persp' or similar functions) and specify these palettes, ocean
areas
> may coloured green (indicating) land, which may be quite confusing.
>
> I have looked through various packages, and have found several colour
> palette functions, but none that do what I need.
>
> Basically, I just need a function that takes a vector of elevation
> values as input, and outputs a vector of 'natural' colours. For  
> negative
> values (i.e., ocean), the 'blue' colours of 'topo.colors'
would be OK,
> and for positive values either the colours of 'terrain.colors' or
the
> non-blue colours of 'topo.colors' would look nice.
>
> It is of course not very difficult to create such a function myself,
> e.g. using the 'cut' function and a standard palette. But perhaps
> somebody has already has made one?
>
> My ideal topographic colour mapping function would support separate
> colour levels for water and land (so that you can specifiy for  
> example 5
> colours of water, from a depth of 5000 meters to 0 meters, and 20
> colours of land, from a depth of 0 meters to 2000 meters), support
> several nice palettes, and also support logarithmic colour mapping.  
> But
> 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.

>
> -- 
> Karl Ove Hufthammer
>
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