[R-sig-Geo] gstat::variogram - distance calculation is incorrect; kriging on sphere

[Edzer Pebesma]

That's right; my fault that I sent the email and updated the sp package 
on CRAN almost at the same time. The new sp (0.9-27 would suffice) 
should now have propagated to your mirror, simply update your sp package 
again and it should work. Let me know if it doesn't.
--
Edzer

Greg Lee wrote:
> Hello Edzer,
>
> I was curious to run the example you provided (using the latest CRAN
> versions of all packages), but as written the line
>
>   
>> idw.spdf = as(idw.out, "SpatialPolygonsDataFrame")
>>     
>
> produces
>
> Error in as(idw.out, "SpatialPolygonsDataFrame") :  no method or default for
> coercing "SpatialPixelsDataFrame" to "SpatialPolygonsDataFrame"
> Regards,
> Greg.
>
>
> 2008/10/30 Edzer Pebesma <edzer.pebesma at uni-muenster.de>
>
>   
>> Dear all,
>>
>> In continuation of this thread, I've spent some time looking at kriging on
>> the sphere, corrected some bugs, and need further help.
>>
>> First of all, distances for covariances on the sphere were computed
>> incorrectly as well in gstat, so I hope not too many people have been
>> relying on this--kriging seemed to happen still in some Euclidian mode. The
>> good news is that it seems to work now (gstat 0.9-53, accepted on CRAN).
>> Inverse distance interpolation for spherical data seemed to work already.
>>
>> Covariances on the sphere now work, but the models present do not include
>> those specially deviced for spherical data. Can anyone provide me with or
>> point me to useful, preferably simple covariance functions that are positive
>> definite on the sphere? The example below seems to work but in certain cases
>> without nugget the interpolation may go crazy. You'll need to update your sp
>> to 0.9-27 to run it (also accepted on CRAN).
>>
>> Below is an example script. It also needs the new sp and gstat versions.
>>
>> library(gstat)
>> library(rgdal)
>> world = expand.grid(long=seq(-177.5,177.5,5),lat=seq(-87.5,87.5,5))
>> world.sp = SpatialPixels(SpatialPoints(world,CRS("+proj=longlat")))
>> plot(world.sp,axes=T)
>>
>> pts=data.frame(long=runif(100,-180,180),lat=runif(100,-90,90),val=rnorm(100))
>> coordinates(pts)=~long+lat
>> proj4string(pts)=CRS("+proj=longlat")
>> points(pts,col='red')
>>
>> # inverse distance interpolation on the sphere:
>> idw.out = idw(val~1,pts,world.sp)
>> image(idw.out, axes = TRUE, ylim = c(-90,90))
>> points(pts, pch=3)
>> idw.spdf = as(idw.out, "SpatialPolygonsDataFrame")
>> newproj = CRS("+proj=moll")
>> idw.spdf.moll = spTransform(idw.spdf, newproj)
>> spplot(idw.spdf.moll, "var1.pred",col.regions=bpy.colors(),col=0,
>>   sp.layout = list(sp.points, spTransform(pts, newproj), col = 'black'))
>>
>> # kriging on the sphere
>> kr.out = krige(val~1,pts,world.sp,vgm(1, "Exp", 3000))
>> idw.spdf.moll$kr = kr.out[[1]]
>> spplot(idw.spdf.moll, "kr", col.regions=bpy.colors(), col=0,
>>   sp.layout = list(sp.points, spTransform(pts, newproj), col = 'black'))
>>
>> --
>> Edzer Pebesma
>> Institute for Geoinformatics (ifgi), University of Münster
>> Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
>> 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/
>> http://www.springer.com/978-0-387-78170-9 e.pebesma at wwu.de
>>
>>
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>>
>>
>>     
>
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/
http://www.springer.com/978-0-387-78170-9 e.pebesma at wwu.de