[R-sig-Geo] Extract xy coordinates from raster of interesting neighborhood cells

[Ben Tupper]

Hi,

I'm not sure why you expect 24 points - you have 4 locations and for each you want the 4 bishop's directions - so, I think at most you should expect 16 points.  See http://www.lpc.uottawa.ca/publications/moransi/moran.htm <http://www.lpc.uottawa.ca/publications/moransi/moran.htm> for where I expect 4 points for bishop's for each input location; perhaps you have a different idea of bishop's direction?  

Your second point [45.12069, -88.369745] is on to the southern edge of the raster - so it can't find points southward - only the 2 northward.

Finally, it may not make any difference at all, but your pts_s has no coordinate reference.  Below I show where I assign the same projection as your raster.  I also don't have 'land_mask' so I reused 'r' and used xyFromCell to backwards extract the adjacent cell coordinates.

Does that do the trick for you?

Cheers,
Ben

### START
require(raster)
require(sp)

## Create a raster
r <- raster(nc=30, nr=30)
r <- setValues(r, round(runif(ncell(r))* 255))
plot(r)

##Given interesting points coordinates
xd     <- c( -24.99270,   45.12069,  99.40321,  73.64419)
yd     <- c(-45.435267, -88.369745, -7.086949, 44.174530)
pts <- data.frame(xd,yd)
pts_s<- SpatialPoints(pts)
projection(pts_s) <- projection(r)
points(pts_s, col="red", pch=16)

## Find pixels center of each point 
N_cells <- cellFromXY(r, pts_s)

e <- adjacent(r, N_cells , directions='bishop', id=TRUE, sorted = TRUE)
xy <- xyFromCell(r, e[,'to'], spatial = TRUE)


#Visualization

plot(r)
points(pts_s, col="red", pch=16)
points(xy, col="black", pch=16)
### END





> On May 30, 2018, at 3:11 PM, ASANTOS via R-sig-Geo <r-sig-geo using r-project.org> wrote:
> 
> Dear R-Sig-Geo Members,
> 
>     I've like to extract xy coordinates from raster of 24 neigborhood cells that surround the 4 given points (pts_s) pixels and for this I used:
> 
> #Packages
> 
> require(raster)
> require(sp)
> 
> ## Create a raster
> r <- raster(nc=30, nr=30)
> r <- setValues(r, round(runif(ncell(r))* 255))
> plot(r)
> 
> ##Given interesting points coordinates
> xd     <- c(-24.99270,45.12069,99.40321,73.64419)
> yd  <- c(-45.435267,-88.369745,-7.086949,44.174530)
> pts <- data.frame(xd,yd)
> pts_s<- SpatialPoints(pts)
> points(pts_s, col="red", pch=16)
> 
> ## Find pixels center of each point (My idea is not to use the original point coordinates, but coordinates of the center of interesting pixel).
> N_cells <- cellFromXY(r, pts_s)
> 
> 
> # Extract xy coordinates from raster of 24 neighborhood cells given pixel number N_cells
> e<-adjacent(r, N_cells , directions='bishop', id=TRUE)
> coordinates(land_mask)[e[,1],] ## Doesn't return 24 neighborhood by N_cells object
> ng_coords<-coordinates(land_mask)[e[,1],]
> #
> 
> #Visualization
> 
> plot(r)
> points(pts_s, col="red", pch=16)
> points(ng_coords, col="black", pch=16)
> ##
> 
>     But I don't have success because the ng_coords object is not a 24 neighborhood cells of each point that I search. There are solution for this?
> 
> Thanks in advance,
> 
> Alexandre
> 
> -- 
> ======================================================================
> Alexandre dos Santos
> Proteção Florestal
> IFMT - Instituto Federal de Educação, Ciência e Tecnologia de Mato Grosso
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> 
>        alexandre.santos using cas.ifmt.edu.br
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> 
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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/






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