[R-sig-Geo] Detect and summarize changes in categorical raster

[Thiago V. dos Santos]

Hi all,

I am trying to detect and summarize changes in categorical rasters.


I have two rasters. Each raster is a land use map, with values ranging from 1 to 15 and representing different land-use classes. r1 is my control scenario, and r2 is my climate change scenario where changes in climate induce changes in land use classes.

Here is some example data:

## scratch a raster brick with 120 timesteps (10 years)
r2 <- r1 <- brick(nrows=18, ncols=36, xmn=0, xmx=18, ymn=0, ymx=36, nl=120)

## fill some random values
set.seed(4)
r1[] <- round(runif(18 * 36 * 120, min=1, max=15), digits=0)

set.seed(5)
r2[] <- round(runif(18 * 36 * 120, min=1, max=15), digits=0)



What I would like to do is for each time step (brick layer), compare each cell of r2 relative to r1 in this way:
 - is the value different? yes/no
 - if yes, what was the change? for example 1 to 10, or 2 to 7 and so on.

By the end, I would like to be able to:
  - plot a map showing the occurence of changes
  - have a table with the frequency of changes in each class (i.e. 1 to 10, 2 to 7 etc)

Is there any tool to perform this analysis in R? Which one?

If no, what would be the best approach to implement that by myself?
 Thanks in advance,
--
Thiago V. dos Santos
PhD student
Land and Atmospheric Science
University of Minnesota
http://www.laas.umn.edu/CurrentStudents/MeettheStudents/ThiagodosSantos/index.htm
Phone: (612) 323 9898