Image colours based on certain values
On Mon, 3 Sep 2007, Michal Gallay wrote:
Dear R Spatial Users,
I have many DEM ASCII grid files and have produced maps(images) via
image(). The maps display e.g. slope angle, profile curvature for one area,
but calculated via different methods.
I have searched R help, the R group, but I couldn't find out how to make R
use certain colours for certain image values, in order to be able to
compare the maps, for instance to have the same color for 0 curvature
values, no matter what is the range of values.
If it helps, the following is applied in a 'for' loop for 20 files:
raster.values <- read.asciigrid(fname=Files[i], as.image = FALSE,
plot.image = FALSE, colname = Files[i])
min.val <- min(raster.values at data, na.rm=TRUE)
max.val <- max(raster.values at data, na.rm=TRUE)
image(raster.values, zlim=c(min.val,max.val), col=bpy.colors(255,
cutoff.tails = 0.1), axes=TRUE)
Set breaks= explicity, it will be passed through to image.default(); perhaps do not set zlim=, and note that there should be one more break than the number of colours. Roger
I appreciate and thank you for help. Michal
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no