On Fri, 14 Mar 2008, Murray Richardson wrote:
Hi Roger and others,
Thanks again for this helpful script. It made me see some potential to use
spdep package for another related problem that I was previously using CGAL
(C++) alpha shapes for.
Is there a way to output a list of nearest neighbour pairs in an xy
coordinate list (or binary grid for that matter I guess). I would like to
convert a binary grid of lines (1 cell thick) to a constituent line segment
list of the form (startx, starty, end x end y), which I then polygonize using
RODBC/postGIS, as we discussed in a previous thread.
Would nb2lines() in spdep help? It was written for a user wanting to write
a shapefile of lines, so I guess that it either is what you are looking
for, or close enough to serve as an example?
Roger
Thanks in advance!
Murray
Roger Bivand wrote:
On Wed, 12 Mar 2008, Agustin Lobo wrote:
> and a combination of r.clump and r.stats
> in grass (which is "linked" to R) can also do the job.
Yes, that will be very robust. I've tried an R attack through neighbour
lists:
library(sp)
data(meuse.grid)
coordinates(meuse.grid) <- c("x", "y")
gridded(meuse.grid) <- TRUE
fullgrid(meuse.grid) <- TRUE
class(meuse.grid)
names(meuse.grid)
meuse.grid$ffreq1 <- meuse.grid$ffreq == 1
is.na(meuse.grid$ffreq1) <- !meuse.grid$ffreq1
image(meuse.grid, "ffreq1")
pix <- as(meuse.grid["ffreq1"], "SpatialPixelsDataFrame")
summary(pix)
image(pix)
library(spdep)
nb_rook <- dnearneigh(coordinates(pix), 0, 41)
nb_queen <- dnearneigh(coordinates(pix), 0, 57)
comp_rook <- n.comp.nb(nb_rook)
comp_queen <- n.comp.nb(nb_queen)
t_rook <- table(comp_rook$comp.id)
t_queen <- table(comp_queen$comp.id)
t_rook
t_queen
pix$rook <- comp_rook$comp.id
pix$queen <- comp_queen$comp.id
image(pix, "rook", col=rainbow(31))
pix$nrook <- t_rook[pix$rook]
pix$nqueen <- t_queen[pix$queen]
summary(pix)
image(pix, "nqueen")
spplot(pix, "nqueen")
using cut-off distances for distance-based neighbours just larger than the
resolution and the diagonal resolution. There were only 779 cells in
patches here, but it ran so fast that scaling up shouldn't be a problem.
Roger
>
> Agus
>
> Andrew Niccolai escribió:
> > If you aren't dedicated to an R specific solution, ImageJ is open
> > source and
> > does this under Analysis/Binary.
> >
> > -----Original Message-----
> > From: [EMAIL PROTECTED]
> > [mailto:[EMAIL PROTECTED] On Behalf Of Murray
> > Richardson
> > Sent: Wednesday, March 12, 2008 12:59 PM
> > To: r-sig-geo@stat.math.ethz.ch
> > Subject: [R-sig-Geo] enumerate grid clusters/patches with size of
> > contiguous
> > cluster
> >
> > Hello friends,
> >
> > I am trying to take a binary input grid of patches (connected cells
> > with
> > value = 1), and assign to each non-zero cell the total number of
> > pixels
> > comprising the patch to which it belongs.
> >
> > So for a connected patch of 27 pixels, all cells belonging to that
> > patch
> > will have a value of 27.
> >
> > Just wondering if anyone has any suggestions. Maybe a function I
> > don't
> > know about yet...
> >
> > Thanks in advance,
> >
> > Murray Richardson
> >
_______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo@stat.math.ethz.ch
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
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> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
>
>
--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [EMAIL PROTECTED]
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