[R-sig-Geo] Assign a unique ID number to each patch in a raster

[Agustin Lobo]

I think Nelly points out that package raster lacks a more general
clumping tool (i.e., the equivalent to r.clump in grass) that I've
often missed too.
I'm not sure circumventing the way Ben suggest would work for large
raster layers, for which package raster was designed.
I have a note to myself regarding this
https://gist.github.com/johnbaums/6d155cfca28e02b05ad5
and
www.openforis.org/tools/geospatial-toolkit.html
but have not tried it.

Agus

On Fri, Jan 27, 2017 at 1:19 AM, Ben Tupper <btupper at bigelow.org> wrote:
> Hi,
>
> I think you are asking for connected component labeling. raster::clump() expects your features to be like islands surrounded by NA or 0 background. There might be more Raster* centric ways to do it, but you could use plain old vanilla image processing using the very good imager package ( https://cran.r-project.org/web/packages/imager/ <https://cran.r-project.org/web/packages/imager/> ).  The steps below show in color your actual values with the connected component IDs labeled on each cell.  I used the 8-connected labeling but 4-connected is also available.
>
> library(raster)
> library(imager)
>
> set.seed(10)
> nc <- 8
> nr <- 8
> MIN <- 1
> MAX <- 4
> LUT <- c("orange", "green", "darkgoldenrod", "cornflowerblue")
>
> r <- raster(ncols=nc, nrows=nr)
> r[] <- round(runif(ncell(r),MIN, MAX),digits=0)
> cc <- r
>
> img <- imager::as.cimg(as.matrix(r))
> labeled <- imager::label(img, high_connectivity = TRUE)
> cc[] <- as.matrix(labeled)
>
> plot(r, col = LUT)
> txt <- cc[]
> xy <- raster::xyFromCell(cc, 1:raster::ncell(cc))
> text(xy[,1], xy[,2], txt )
>
>
> Cheers,
> Ben
>> On Jan 26, 2017, at 4:48 PM, Nelly Reduan <nell.redu at hotmail.fr> wrote:
>>
>> Hello,
>> I would like to assign a unique ID number to each patch (a patch is composed of a set of adjacent cells) as shown in this figure:
>>  <2328.png>
>>
>> I tested the clump function (package raster) by applying an eight adjacent cells rule but this function mixes all cell values into single patch.
>>
>> Here is a code example to create a raster. The raster contains values ranged from 1 to 9.
>> r <- raster(ncols=12, nrows=12)
>> r[] <- round(runif(ncell(r),1,9),digits=0)
>> plot(r)
>>
>> Is there a way to assign a unique ID number to grouping cells that form a patch for each class (i.e., values 1, 2, 3, 4, 5, 6, 7, 8, 9) ?
>>
>> Thanks a lot for your time
>> Nell
>>
>>
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> Ben Tupper
> Bigelow Laboratory for Ocean Sciences
> 60 Bigelow Drive, P.O. Box 380
> East Boothbay, Maine 04544
> http://www.bigelow.org
>
>
>
>
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