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

[Hugo Costa]

Hi Ben,
thank you for your help. Clump is a possibility, however I was looking for
something different. In my real data, 9 rasters have to be merged (1
central raster and the 8 surrounding rasters), and running clump after
merging 9 rasters is slow and memory consuming. And this has to be repeated
thousands of times (hopefully in parallel with the rasters in memory). I
didn't explain these details to make the message short.
I'll continue searching for more alternatives, and all ideas are welcome.
Thanks
Hugo

Ben Tupper <btupper using bigelow.org> escreveu no dia sexta, 23/11/2018 à(s)
23:58:

> 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]]
> >
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo using r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
> 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/
>
>
>
>
>
>

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