[R-sig-Geo] GStat kriging using spherical geometry

[Helen Greatrex]

Dear all,

Does anyone know if the Gstat package in r offers kriging using 
spherical geometry rather than euclidean distances?

I couldn't find anything in ?krige or online,  but I've heard that the 
general gstat package includes this option.  From comparisons with a 
different kriging code outside r, the inclusion of spherical geometry 
does make a difference to my results, but I'd really like to use gstat!

For some context, I'm block kriging rainfall data using lat long 
coordinates.  An example of my code is below.  To make things simple, in 
this example I'm aiming to krige over a 1 degree block centred at (39.5, 
7.5)
(So the corners of the block would be [39,7],[40,7],[40,8],[39,8])
Note, In general I wouldn't be kriging over a block this size - it's 
just to make the code simple!

Best wishes and thank you for your time
Helen

---------------------------------------------------------------------------

 ># Read in the input files
 >##############################
 >  dayinput <- file("zsourcep.txt","r")
 >  mydata <- read.table(dayinput,header=TRUE)
 >  unlink("zsourcep.txt")
 >
 >
 ># Read in the output files
 >##############################
 >  dayoutput <- file("ztarget.txt","r")
 >  mydataout <- read.table(dayoutput,header=TRUE)
 >  unlink("ztarget.txt")
 >
 >
 ># Turn these into the correct format for krige
 >##############################
 >  cinput <- data.frame (Long = mydataout$Long, Lat= mydataout$Lat     
                              )
 >  input  <- data.frame  (Long = mydata$Long ,     Lat=mydata$Lat,      
Value=mydata$Value)
 >  coordinates(input)  <- ~ Long + Lat
 >  coordinates(cinput)<- ~ Long + Lat
 >
 >
 ># Now make the variogram model
 >##############################
 >  m <- vgm(.675, "Exp", 9.51, 0.237)
 > >
 ># And krige
 >##############################
 >  x <- krige(Value ~ 1, input,cinput , model = m, block=c(1,1))
  [using ordinary kriging]
 >  x
     coordinates var1.pred  var1.var

-- 
-----------------------------
Helen Greatrex (PhD Student)
Room 1U09
Department of Meteorology
University of Reading
Earley Gate
PO Box 243
READING
RG6 6BB