Dear all,
I have a question related to the function xvalid (package geoR), which I asked
on StackOverflow before but unfortunately did not get answered, probably
because it is too specifically related to spatial statistics and this specific
function
(http://stackoverflow.com/questions/43520716/cross-validation-for-kriging-in-r-how-to-include-the-trend-while-reestimating-t).
I hope anyone of you is able to answer it.
I would like to compute a variogram, fit it, and then perform cross-validation.
Function xvalid seems to work pretty nice to do the cross-validation. It works
when I set reestimate=TRUE (so it reestimates the variogram for every point
removed from the dataset in cross-validation) and it also works when using a
trend. However, it does not seem to work when combining these two. Here is a
reproducible example using the Meuse example dataset:
library(geoR)
library(sp)
data(meuse) # import data
coordinates(meuse) = ~x+y # make spatialpointsdataframe
meuse@proj4string <- CRS("+init=epsg:28992") # add projection
meuse_geo <- as.geodata(meuse) # create object of class geodata for geoR
compatibility
meuse_geo$data <- meuse@data # attach all data (incl. covariates) to meuse_geo
meuse_vario <- variog(geodata=meuse_geo, data=meuse_geo$data$lead, trend=
~meuse_geo$data$elev) # variogram
meuse_vfit <- variofit(meuse_vario, nugget=0.1, fix.nugget=T) # fit
# cross-validation works fine:
xvalid(geodata=meuse_geo, data=meuse_geo$data$lead, model=meuse_vfit,
variog.obj = meuse_vario, reestimate=F)
# cross-validation does not work when reestimate = T:
xvalid(geodata=meuse_geo, data=meuse_geo$data$lead, model=meuse_vfit,
variog.obj = meuse_vario, reestimate=T)
The error I get is:
Error in variog(coords = cv.coords, data = cv.data, uvec = variog.obj$uvec, :
coords and trend have incompatible sizes
It seems to remove the point from the dataset during cross-validation, but it
doesn't seem to remove the point from the covariates/trend data. Any ideas on
solving this / work-arounds? Thanks a lot in advance for thinking along.
Best, Vera
---
V.M. (Vera) van Zoest, MSc | PhD candidate |
University of Twente<http://www.utwente.nl/> | Faculty ITC<http://www.itc.nl/>
| Department Earth Observation Science (EOS)<https://www.itc.nl/EOS> |
ITC Building, room 2-038 | T: +31 (0)53 - 489 4412 |
v.m.vanzo...@utwente.nl<mailto:v.m.vanzo...@utwente.nl> |
Study Geoinformatics:
www.itc.nl/geoinformatics<http://www.itc.nl/geoinformatics>
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