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How to extract the index (i, j) row and column from a raster?

4 messages · Alex, Lionel, Rafael Wüest +1 more

Original
Lionel
# 
The easiest way is to use the function 'values' which return the values 
of a raster row by row:

r<-raster(nrows=10,ncols=10)
r[]<-rnorm(100)
data<-data.frame(X=rep(1:10,each=10),Y=rep(1:10,10),Z=values(r))
head(data)

Cheers,
Lionel
On 19/06/2013 12:42, Alex wrote:
Rafael Wüest
# 
Well, if the ultimate aim is to build a polygon from a raster, I suggest you look at

library(raster)
?rasterToPolygons

Rafael
On 19.06.2013, at 13:00, Lionel Hertzog <s6lihert at uni-bonn.de> wrote:

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        
--
Rafael W?est
Swiss Federal Research Institute WSL
Z?rcherstrasse 111
8903 Birmensdorf
Switzerland

+41 44 7392126
rafael.wueest at wsl.ch
http://www.wsl.ch/info/mitarbeitende/wueest/index_EN

  
  


  


      

    

    

      
      

        


  

        

      Forrest Stevens
    

    

      
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I think the first part of what you're looking for is in the raster
package.  You can load your raster file using the raster() function
(instead of creating one from scratch as in the example below).  Then
use the rasterToPoints() function to convert to a matrix object:

require(raster)
r <- raster(nrow=10, ncol=10, xmn=0, xmx=10, ymn=0, ymx=10, crs=NA)
r[] <- runif(ncell(r))
r[r<0.5] <- NA

xyz <- rasterToPoints(r)

            

      
      
      
    

        
convert to polygons via a variety of paths.  But if it's just a subset
of values you're looking to convert you might look at the
rasterToPolygons() function as well, it may do what you need.

Sincerely,
Forrest

        
On Wed, Jun 19, 2013 at 6:42 AM, Alex <alxcart at gmail.com> wrote: