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

[Vijay Lulla]

Or you can try something like this?

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

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

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)

N_cells <- cellFromXY(r, pts_s)
e<-adjacent(r, N_cells , directions='bishop', pairs=FALSE)

ng_coords <- xyFromCell(r, e)
plot(r)
points(pts, col='red', pch=16)
points(ng_coords, col='black', pch=16)


### Alternative to what Ben suggested!
## Set neighborhood matrix.  Focal cell is 0 while neighbors are 1!!
neigh <- matrix(1L, nrow=5, ncol=5); neigh[3,3] <- 0L
e1<-adjacent(r, N_cells , directions=neigh, pairs=FALSE)
ng_coords1 <- xyFromCell(r, e1)
plot(r);
points(pts, col='red', pch=16);
points(ng_coords, col='black', pch=16);
points(ng_coords1, col='blue', pch=16)
### END

HTH,
Vijay.

On Wed, May 30, 2018 at 4:22 PM, Ben Tupper <btupper using bigelow.org> wrote:

> 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
> > Campus Cáceres
> > Caixa Postal 244
> > Avenida dos Ramires, s/n
> > Bairro: Distrito Industrial
> > Cáceres - MT                      CEP: 78.200-000
> > Fone: (+55) 65 99686-6970 (VIVO) (+55) 65 3221-2674 (FIXO)
> >
> >        alexandre.santos using cas.ifmt.edu.br
> > Lattes: http://lattes.cnpq.br/1360403201088680
> > OrcID: orcid.org/0000-0001-8232-6722
> > Researchgate: www.researchgate.net/profile/Alexandre_Santos10
> > LinkedIn: br.linkedin.com/in/alexandre-dos-santos-87961635
> > Mendeley:www.mendeley.com/profiles/alexandre-dos-santos6/
> >
> > _______________________________________________
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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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-- 
Vijay Lulla, Ph.D.

Assistant Professor,
Dept. of Geography, IUPUI
425 University Blvd, CA-207C.
Indianapolis, IN-46202
vlulla using iupui.edu

<http://vijaylulla.com>
http://vijaylulla.com

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