[R-sig-Geo] Write GeoTiff with color table

[Paul Hiemstra]

Paul Hiemstra schreef:
> Ned Horning schreef:
>> Hi - Is it possible to output an Indexed (single band byte image) 
>> GeoTiff using a predefined look-up-table in R? For now I output a 
>> byte GeoTiff file from R and then import it into GRASS, create a 
>> color table, and then export that as a colored GeoTiff. That works 
>> fine but it would be nice to be able to create the colored GeoTiff 
>> directly in R.
>>
>> All the best,
>>
>> Ned
>>
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>> R-sig-Geo at stat.math.ethz.ch
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> Hi,
>
> You can create color RGB tiffs using the functions I wrote once. Hope 
> it helps!
>
> Paul
>
> val2rgb = function(val, color, at)
> # Function to map the value to an RGB value
> {
>    for(i in 1:length(at))
>    {
>        if(val <= at[i]) return(color[i])
>    }
>    return(color[length(color)])
> }
>
> writeTIFF = function(data, column_name, file, color, at, style = 
> "quantile")
In addition: the style argument should be left out.

cheers and goodluck,
Paul
> # Function to construct a color (RGB) GeoTIFF
> #
> # data :        The data for making the GeoTIFF
> # file :        file for storing the tif file
> # column_name : The name of the column in 'data' that is used for the 
> GeoTIFF
> # color :       A list with the colors that will be used. Most used is 
> output
> #               from functions such as 'rainbow' and 'RColorBrewer'.
> # at :          The data values where the colors change.
> {
>        print(paste("writing",file))
>
>    data2color = sapply(data[[column_name]], FUN = function(x) 
> val2rgb(x, color,
>    data2rgb = col2rgb(data2color)
>
>    data$band1 = data2rgb["red",]
>    data$band2 = data2rgb["green",]
>    data$band3 = data2rgb["blue",]
>
>    writeGDAL(data[c("band1","band2","band3")],file,type="Byte")
> }
>


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone:  +3130 274 3113 Mon-Tue
Phone:  +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul