get coordinates of centroids in a SpatialGridDataFrame object.

I have a classified images imported as SpatialGridDataFrame. I'd like to get
centroid coordinates of regions of cells with common values, considering the
"islands" that represents objects in space.

If you are thinking of "connected components", try labcon() in adehabitat:

library(adehabitat)
data(puechabon)
hr <- getsahrlocs(puechabon$sahr, "hr")
u <- getkasc(hr, "Jean")
p <- labcon(u)
c2a <- kasc2spixdf(as.kasc(list(p)))
names(c2a) <- "patches"
image(c2a)
c2b <- as.SpatialPolygons.SpatialPixels(c2a)
library(maptools)
c2c <- unionSpatialPolygons(c2b, c2a$patches)
plot(c2c, axes=TRUE)
points(coordinates(c2c), pch=3)

How this scales for your data is another matter.

Roger

Any idea?

____________

Paulo E. Cardoso




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