Jan Holstein <jan.holstein <at> awi.de> writes:
>
> I noticed that dnearneigh::spdep shows diverging behaviour with matrix and
> SpatialPoints objects respectively:
>
> reproducible example:
>
> library(spdep)
> set.seed(5)
> spdf<-SpatialPointsDataFrame(cbind(lon=runif(1000,2,8),lat=runif(1000,53,56)),
> data=data.frame(par=runif(1000,0,1)),coords.nrs =
> numeric(0),proj4string=CRS("+init=epsg:4326"))
Thanks for a reproducible example; posting on R-sig-geo would have elicited
an earlier response.
This will only generate compliant behaviour when rgdal is loaded, converting
+init=epsg:4326 to +init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs
+ellps=WGS84 +towgs84=0,0,0, so that is.projected(spdf) is FALSE
>
> dnearneigh(x=coordinates(spdf), d1=0, d2=20,longlat = TRUE)
> #Neighbour list object:
> #Number of regions: 1000
> #Number of nonzero links: 9504
> #Percentage nonzero weights: 0.9504
> #Average number of links: 9.504
> #2 regions with no links:
> #449 619
>
> but ...
There is a bug in the logic, but:
dnearneigh(as(spdf,"SpatialPoints"), 0, 20)
#Neighbour list object:
#Number of regions: 1000
#Number of nonzero links: 9288
#Percentage nonzero weights: 0.9288
#Average number of links: 9.288
which was the intention - either provide an object inheriting from
SpatialPoints, with longlat set internally, or set it manually. Following
the removal of the logic bug:
dnearneigh(as(spdf,"SpatialPoints"), 0, 20, longlat = TRUE)
#Neighbour list object:
#Number of regions: 1000
#Number of nonzero links: 9288
#Percentage nonzero weights: 0.9288
#Average number of links: 9.288
#Warning message:
#In dnearneigh(as(spdf, "SpatialPoints"), 0, 20, longlat = TRUE) :
# dnearneigh: longlat overriden for Spatial object
Coercion to SpatialPoints isn't needed - the function looks for objects
inheriting from SpatialPoints, so just spdf is sufficient.
Bugfix on R-forge at revision 552.
Roger
> dnearneigh(as(spdf,"SpatialPoints"), 0, 20,longlat = TRUE)
> #Neighbour list object:
> #Number of regions: 1000
> #Number of nonzero links: 999000
> #Percentage nonzero weights: 99.9
> #Average number of links: 999
>
> it seems that 'dnearneigh' ignores longlat=TRUE if class(x)==SpatialPoints,
> since
>
> dnearneigh(x=coordinates(spdf), d1=0, d2=20,longlat = FALSE)
> #Neighbour list object:
> #Number of regions: 1000
> #Number of nonzero links: 999000
> #Percentage nonzero weights: 99.9
> #Average number of links: 999
>
> gives the same 'undesired' result.
>
> -----
> Jan M. Holstein, Dept. Functional Ecology, Alfred Wegener Institut for
Polar and Marine Research (AWI)
> --
>
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