[R-sig-Geo] create nb object
Roger.Bivand at nhh.no
Thu Dec 17 09:14:38 CET 2009
On Wed, 16 Dec 2009, Pete Larson wrote:
> Hello all,
> I have a data frame with lat and lon coordinates for some sample areas (not a
> grid) .
> I was to create an nb object that I can use with spdep but am unsure as to
> how to convert it.
> Does anybody have any ideas?
Create a matrix of coordinates, if not using sp classes, for example:
xy <- cbind(df$x, df$y)
or if your data frame is a SpatialPointsDataFrame, just:
xy <- coordinates(obj)
Then your choice of dnearneigh(), knn2nb(knearneigh()), graph2nb() with
three graph variants, tri2nb() for a Delaunay triangulation. The first two
of these also take a longlat= argument in case your coordinates are
geographical, not projected. Triangulation and graph-based methods need
planar coordinates, so you would have to project them first.
Hope this helps,
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> R-sig-Geo at stat.math.ethz.ch
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e-mail: Roger.Bivand at nhh.no
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