On Fri, 27 Nov 2009, rusers.sh wrote:
Dear Robert,
My method to generate the Voronoi tessellation maybe not better, You can
show me you method to get it.
What i want to get is the the class of SpatialPolygons(sp) based on the
generated Voronoi tessellation.
Any ideas or suggestions are greatly appreciated.
In the list archives for March 2007 (search in Nabble, for example), there
are hints. A more up to date version might be:
set.seed(1)
crds <- cbind(runif(100), runif(100))
library(deldir)
z <- deldir(crds[,1], crds[,2])
w <- tile.list(z)
library(sp)
polys <- vector(mode="list", length=length(w))
for (i in seq(along=polys)) {
pcrds <- cbind(w[[i]]$x, w[[i]]$y)
pcrds <- rbind(pcrds, pcrds[1,])
polys[[i]] <- Polygons(list(Polygon(pcrds)), ID=as.character(i))
}
SP <- SpatialPolygons(polys)
SPDF <- SpatialPolygonsDataFrame(SP, data=data.frame(x=crds[,1],
y=crds[,2], row.names=row.names(SP)))
plot(SPDF)
points(crds, pch=3, col="red")
text(coordinates(SPDF), label=row.names(SPDF))
then export the SpatialPolygonsDataFrame in the usual way.
By the way, to get the centroids (aka label points) for Polygons objects,
use coordinates() on their enclosing SpatialPolygons object. The (very)
deprecated maptools function you refered to in an earlier posting will
cease to be available very shortly.
Hope this helps,
Roger
2009/11/27 rusers.sh <rusers...@gmail.com>
Yes, what i want is really the Voronoi tessellation that you showed in
the link. I can generate the Voronoi tessellation (see my codes), but my
problem is how to generate the the class of SpatialPolygons(sp) based on the
generated Voronoi tessellation? (SHP means shape file of polygon.)
Thanks a lot.
####My code to get the Voronoi tessellation########
library(spatstat)
win<-owin(c(0,1),c(0,1))
pp <- runifpoint(10,win=win)
#plot(pp)
library(tripack)
vm <- voronoi.mosaic(pp$x,pp$y)
plot(vm)
par(new=T)
points(pp$x,pp$y,col='blue')
axis(1,xlim=c(0,1)) #1=below
axis(2,ylim=c(0,1)) #2=left
box(xlim=c(0,1),ylim=c(0,1))
2009/11/27 Robert J. Hijmans <r.hijm...@gmail.com>
I think you want a Voronoi tessalation (diagram):
http://en.wikipedia.org/wiki/Voronoi_diagram
But what are SHP polygons? Is 'SHP' a class in an R package?
Robert
On Fri, Nov 27, 2009 at 2:03 PM, rusers.sh <rusers...@gmail.com> wrote:
To make this problem more clear. Suppose i have some points in a
certain
area (e.g. 10 points in a unit square), how to cut and generate the
corresponding SHP polygons of containing the points (1 point in 1
polygon,
maybe the point as their centroid) in this certain area?
In GeoDa, there is a menu "tools->shape->point to polygon" to achieve
that. I wonder how to do that in R. Thanks a lot.
##Example##
win<-owin(c(0,1),c(0,1))
pp <- runifpoint(10) #generate 10 points
#i want to change these 10 points into 10 SHP polygons,something like
the
manipulation in GeoDA, "tools->shape->point to polygon"
#plot(pp)
2009/11/27 rusers.sh <rusers...@gmail.com>
Hi,
I always need to convert between the points and polygons. For
converting
the polygons to points, we can use the "get.Pcent(maptools) " to get
the
centroids of the polygons. But for converting points to polygons
(something
like GeoDa's "tools->shape->point to polygon"), i cannot find the
corresponding method. I searched in R Site Search with "point to
polygon"
and "generate polygon", but still cannot get the answers.
Does anybody know how to convert points to the SHP polygons?
OR whether we can generate some SHP polygons randomly in R?
##Example##
win<-owin(c(0,1),c(0,1))
pp <- runifpoint(10) #generate 10 points
#i want to change these 10 points into 10 SHP polygons,something like
the
manipulation in GeoDA, "tools->shape->point to polygon"
#plot(pp)
Thanks a lot.
--
-----------------
Jane Chang
Queen's
--
-----------------
Jane Chang
Queen's
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--
-----------------
Jane Chang
Queen's
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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: roger.biv...@nhh.no
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