[R-sig-Geo] raster::clump not working?

[João Carreiras]

Dear Ben,

Thank you for your prompt reply.

Now I see what clump does. I just thought clump would give the same
result as ArcGIS "Region Group". I need some command to assign a
different value to each patch. And by patch I mean contiguous pixels
having the same value, so that in this (absurd) example I would get
648 patches.

Take care
Joao

On 25 May 2018 at 11:35, Ben Tupper <btupper using bigelow.org> wrote:
> Hi,
>
> I think it is actually correct - there is only one 'clump' of connected
> cells.  In raster clumps are separated from other clumps by backgound (0 or
> NA).  In your example there is no background anywhere so there is just one
> clump.
>
> You can see the difference if you divide x in to halves with a row of NAs.
> Note that limited spatial extent so the clumping doesn't wrap around the
> globe which it will for [-180, 180].
>
> r <- raster(ncols=36, nrows=18, xmn = 0, xmx = 36, ymn = 0, ymx = 18)
> x <- init(r, fun='cell')
>
> x[9,1:36] <- NA
> y <- clump(x)
> y
> # class       : RasterLayer
> # dimensions  : 18, 36, 648  (nrow, ncol, ncell)
> # resolution  : 1, 1  (x, y)
> # extent      : 0, 36, 0, 18  (xmin, xmax, ymin, ymax)
> # coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> # data source : in memory
> # names       : clumps
> # values      : 1, 2  (min, max)
>
> x[1:18, 18] <- NA
> y
> # class       : RasterLayer
> # dimensions  : 18, 36, 648  (nrow, ncol, ncell)
> # resolution  : 1, 1  (x, y)
> # extent      : 0, 36, 0, 18  (xmin, xmax, ymin, ymax)
> # coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> # data source : in memory
> # names       : clumps
> # values      : 1, 4  (min, max)
>
>
> Cheers,
> Ben
>
>
> On May 25, 2018, at 6:00 AM, João Carreiras <jmbcarreiras using gmail.com> wrote:
>
> Hi!
>
> I've been trying to run the clump command but the output is consistently a
> raster with values == 1. Please find below an example.
>
> I'm sure I'm doing something stupid. However, the command is really
> straightforward and I can't seem to identify what the problem might be.
>
> Any help really appreciated.
> Thanks
> Joao
>
> r <- raster(ncols=36, nrows=18)
> x <- init(r, fun='cell')
> x
> class       : RasterLayer
> dimensions  : 18, 36, 648  (nrow, ncol, ncell)
> resolution  : 10, 10  (x, y)
> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> data source : in memory
> names       : layer
> values      : 1, 648  (min, max)
> a <- clump(x)
> a
> class       : RasterLayer
> dimensions  : 18, 36, 648  (nrow, ncol, ncell)
> resolution  : 10, 10  (x, y)
> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> data source : in memory
> names       : clumps
> values      : 1, 1  (min, max)
>
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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/
>
>
>
>
>