Hello! Thanks for your response.
What I was trying to do (and probably explaining it wrong) was to simulate a matrix/raster such that if I looked at a measure of spatial autocorrelation, it would be around 0.9. So I attacked it via my time series train of thought and considered time periods with 0.9, 0.9^2, and so on. Hope this makes better sense now. thanks, Erin Erin M. Hodgess, PhD Associate Professor Department of Computer and Mathematical Sciences University of Houston - Downtown mailto: hodge...@uhd.edu -----Original Message----- From: r-sig-geo-boun...@r-project.org on behalf of Edzer Pebesma Sent: Fri 6/1/2012 3:58 AM To: r-sig-geo@r-project.org Subject: Re: [R-sig-Geo] simulating a particular autocorrelation structure for a raster Erin, I believe the following would do this: xy = expand.grid(x = 1:16, y = 1:16) d = as.matrix(dist(xy)) sim = chol(0.9 ^ d) %*% rnorm(256) require(sp) grd = SpatialPointsDataFrame(SpatialPoints(xy), data.frame(sim=sim)) gridded(grd) = TRUE spplot(grd, col.regions=bpy.colors()) I used distance instead of closeness, so the diagional neighbour cell gets autocorrelation 0.9 ^ sqrt(2), instead of 0.9 ^ 2 as you suggest. To me, the simulations look really funny, so either my procedure is wrong, or the covariance structure as you suggested (or I interpreted) has strange properties in 2D. On 06/01/2012 09:54 AM, Hodgess, Erin wrote: > Dear R Sig Geo People: > > I would like to create a 16x16 raster, say, with autocorrelation structure of > 0.9 for nearest cell, 0.9^2 for 2nd closest, and so on. > > How would I go about generating that, please? > > I thought about putting together a correlation matrix, multiplying, and > throwing in rnorm. But I'm sure that there is something better and easier > already in place. > > Thanks in advance for any help. > > Sincerely, > Erin > > > Erin M. Hodgess, PhD > Associate Professor > Department of Computer and Mathematical Sciences > University of Houston - Downtown > mailto: hodge...@uhd.edu > > > [[alternative HTML version deleted]] > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@r-project.org > https://stat.ethz.ch/mailman/listinfo/r-sig-geo -- 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.52north.org/geostatistics e.pebe...@wwu.de _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo [[alternative HTML version deleted]]
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