Hi there, I use the surf.gls() function to fit a variable measured over a surface. When I plot the predicted surface, there are local minima/maxima in almost every coordinate where data were measured, which seems aberrant. For instance:
x <- c(343,293,343,243,293,343,443,543,593,243,293,343,393,443,493,543,593,143,193,243,293,343,393,443, 493,543,593,193,243,293,343,543,593,643,93,193,243,293,343,393,443,493,543,43,93,143,193,243,293, 343,393,443,493,543,593,193,243,293,343,393,443,493,543,593,643,143,193,243,293,343,443,543,593, 643,693,143,293,393,443,493,543,593,643,243,293,343,393,493,593,643,243,343,393,243,343,393,343) y <- c(720,670,670,620,620,620,620,620,620,570,570,570,570,570,570,570,570,520,520,520,520,520,520,520, 520,520,520,470,470,470,470,470,470,470,420,420,420,420,420,420,420,420,420,370,370,370,370,370,370, 370,370,370,370,370,370,320,320,320,320,320,320,320,320,320,320,270,270,270,270,270,270,270,270,270, 270,220,220,220,220,220,220,220,220,170,170,170,170,170,170,170,120,120,120,70,70,70,20) z <- c(0.66,0.66,0.66,0.66,0.66,0.66,0.67,0.66,0.66,0.66,0.66,0.66,0.67,0.67,0.66,0.66,0.66,0.66,0.66,0.66,0.66, 0.69,0.67,0.67,0.66,0.66,0.66,0.67,0.67,0.66,0.69,0.66,0.66,0.66,0.66,0.67,0.67,0.67,0.78,0.74,0.74,0.68, 0.68,0.66,0.66,0.66,0.66,0.66,0.72,0.72,0.83,0.70,0.66,0.66,0.66,0.67,0.67,0.67,0.67,0.74,0.70,0.70,0.66, 0.66,0.66,0.67,0.67,0.67,0.67,0.67,0.67,0.66,0.66,0.66,0.66,0.67,0.67,0.66,0.67,0.67,0.66,0.66,0.66,0.66, 0.66,0.66,0.66,0.67,0.66,0.66,0.66,0.66,0.66,0.66,0.66,0.66,0.66) dat <- data.frame(x, y, z) kr <- surf.gls(2, expcov, dat, d = 0.7, nx = 1000) prsurf <- prmat(kr, min(x), max(x), min(y), max(y), 500) image(prsurf, col = rainbow(1000)) One can see that local maxima/minima are found where data were measured: points(x, y, cex = 2) The surface I obtain can be visualised here: http://nsa34.casimages.com/img/2013/03/16/130316115621267122.png Thanks for your help, Florent Pantin John Innes Centre Norwich UK ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
