[R-sig-Geo] Conditional Simulation question
Matthew Sokol
sokolmatt at gmail.com
Tue Feb 1 21:11:48 CET 2005
Hello,
My name is Matthew Sokol and I am writing this list serve to ask some
help. Currently I am a master's student at the University of Nevada
and have come across a problem using R that I can not solve.
Here is my problem:
I am using the R package geoR, specifically the function grf to simulate data.
Basically I have a data set that contains an Easting and Northing
coordinate system and a Z value. From this system I wish to perform
Ordinary Kriging. So I run the following command lines in R:
> dat<-read.table("examplepb.dat",header=TRUE)
> geodat<-as.geodata(dat)
> plot(geodat)
> vario<-variog(geodat)
> lines.variomodel(cov.model="gaussian",nugget=1800,cov.pars=c(1400,60),max.dist=150)
Now since I know the Nugget, Sill, and Range for the variogram model,
I wish to simulate more data that follows the same variogram model. So
I run the following command line:
> simdat<-grf(625,grid="reg",nugget=1800,cov.pars=c(1400,60))
Now, the problem with this command is that it produces data on grid
that is 1 x 1 (all the Northing and easting coordinates are now a
number 0-1). But my easting and northing coordinates have the
following properties:
Easting: Min 254.4 Max: 492
Northing: Min 118 Max 315
Which is not a 1 x 1 grid.
I know my problem is in this statement: grid="reg"
I tried the following commands:
Loci<-expand.grid(seq(250,500,l=250),seq(115,320,l=205))
So now I run:
> simdat<-grf(625,grid=loci,nugget=1800,cov.pars=c(1400,60))
Which produces so much data that I can not R console will not display it.
So I run the following R commands:
geosim<-as.geodata(simdat)
> variosim<-variog(geosim)
variog: computing omnidirectional variogram
Error in vector("double", length) : cannot allocate vector of length 1444504375
So now I get an error. I think i may be producing to much data with my
simulation?
I am lost. I've looked through the manuals but have not found much on
conditional simulation. I was wondering if anyone knew of a problem
like this or where I can look to find more information.
I am sorry if the question is trivial as I have been reading the posts
on this list serve and everyone here has a command of the language far
surpass mine. Thank you for your time.
-Matthew Sokol
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