Write GeoTiff with color table

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

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")

# 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")
}