How to represent certain values in a file as we want?

Question

I have a raster file(1440*720 rows) contains values of 1 ,2 , and 3. when I plot the file , I got a map of three colors but I do not know which is which. How can I put those colors as as I want :

   1=red
   2=blue
   3=green

code:

pvm <- file("C:\\User_sm-das.bin","rb")
cor1<- readBin(pvm, numeric(), size=4,  n=1440*720, signed=TRUE)
r <-raster(t(matrix((data=cor1), ncol=720, nrow=1440)))
image(r)

Answer 1

You can use image.plot from fields which add a legend to the image. Here an example :

First I generate some data :

set.seed(1234)
x<- 1:5; y<- 1:5
z<- matrix(sample(c(1,2,3),25,rep=TRUE),ncol=5,byrow=TRUE)

Then using fields you can have this , it uses the usual image parameters adding a legend.

# fields 
library(fields)
image.plot(x,y,z,col = c("blue" , "red" ,"yellow"),
           interpolate=TRUE) 

Note that if you want to convert your raster matrix to a matrix of color you can do something like this :

## raster 
r <- raster(ncol=5, nrow=5)
values(r) <- z
mm <- matrix(c("blue" , "red" ,"yellow")[values(r)],
             ncol=5,byrow=TRUE)

     [,1]     [,2]   [,3]   [,4]     [,5]    
[1,] "blue"   "red"  "red"  "red"    "yellow"
[2,] "red"    "blue" "blue" "red"    "red"   
[3,] "yellow" "red"  "blue" "yellow" "blue"  
[4,] "yellow" "blue" "blue" "blue"   "blue"  
[5,] "blue"   "blue" "blue" "blue"   "blue"  

The problem with image you can't plot a mtrix of colors you need to have numeric values. But you can use grid.raster from grid package:

library(grid)
grid.raster(mm,interpolate=FALSE)

EDIT

To fix a legend manually you can play with axis.args argument of plot.image

   ## fields 
image.plot(x,y,z,
           col = c("red" , "green" ,"blue"),
           axis.args=list( at=0:3, labels=0:3 ))