[R-sig-Geo] How to sum area of adjacent patches?

[Ben Tupper]

Hi,

I think you may need to use raster::clump() and table() to label your regions.  Check out an old message about clump...

https://stat.ethz.ch/pipermail/r-sig-geo/2017-January/025346.html

It's sort of cumbersome, but I think the following works...


library(raster)
r1<-raster(nrows=10, ncols=10, xmn=0, xmx=1, ymn=0, ymx=1)
r2<-raster(nrows=10, ncols=10, xmn=0, xmx=1, ymn=1, ymx=2)
r1[]<-c(rep(24,24), rep(0,76))
r2[]<-c(rep(0,86), rep(14,14))
par(mfrow=c(3,2)); plot(r1,main="r1"); plot(r2,main="r2")


r3<-merge(r1,r2) ; plot(r3, main="merged rasters")

r3 <- r3
r4[r4>0]<-38     ; plot(r4, main="desired result")

r5 <- clump(r3) ; plot(r5, main = 'clumped')
r5[is.na(r5)] <- 0

r5t <- table(getValues(r5))
for (i in names(r5t)[-1]){
	id <- as.numeric(i)
	print(id)
	r5[r5 == id] <- r5t[i]
}

plot(r5, main = 'relabeled with area')


Cheers,
Ben

P.S. Years ago I used a language called IDL.  It's histogram function has an output keyword called reverse_indices (more here https://www.harrisgeospatial.com/docs/HISTOGRAM.html#H_835179117_677188 and here http://www.idlcoyote.com/tips/histogram_tutorial.html )  - super useful!  Your situation just begs for that same solution in R.





> On Nov 23, 2018, at 5:13 PM, Hugo Costa <hugoagcosta using gmail.com> wrote:
> 
> Deal all,
> 
> I'm merging several rasters representing patches of forest, and the pixel
> values represent the area of the patches. The patches' area should be
> summed along the edges of the merged rasters. I provide a reproducible
> example. Any help is welcome.
> Hugo
> 
> library(raster)
> r1<-raster(nrows=10, ncols=10, xmn=0, xmx=1, ymn=0, ymx=1)
> r2<-raster(nrows=10, ncols=10, xmn=0, xmx=1, ymn=1, ymx=2)
> r1[]<-c(rep(24,24), rep(0,76))
> r2[]<-c(rep(0,86), rep(14,14))
> par(mfrow=c(2,2)); plot(r1,main="r1"); plot(r2,main="r2")
> 
> 
> r3<-merge(r1,r2) ; plot(r3, main="merged rasters")
> 
> # do something
> 
> r3[r3>0]<-38     ; plot(r3, main="desired result")
> 
> 	[[alternative HTML version deleted]]
> 
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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

Ecological Forecasting: https://eco.bigelow.org/