[R] Dampening the spline interpolation for contours

[Craig Stanton]

Hello all,
	I'm very new to R and am having some trouble with the results of the interp function. I'm trying to produce a chart roughly akin to a weather map with natural looking filled contours over a large region of the south pacific. I've got a list of points and values to be mapped to those points and I use the interp function as follows:

tab<-read.table("data.txt")
library("akima")
png("contour.png", width = 1000, height=500)
colourRange<-colorRampPalette(c("#f9cd00","#f9cd00","#f9cd00","#f9cd00","#ffffff","#6afaff","#53a3ff","#53a3ff","#53a3ff"))
filled.contour(interp(x=tab$V1,tab$V2, tab$V3, xo=seq(min(tab$V1), max(tab$V1),length=1000),yo=seq(min(tab$V2), max(tab$V2),length=500), linear = FALSE), xlim = range(160,190),ylim = range(-30,-10), zlim=c(-4,4),color.palette = colourRange   )
dev.off()
rm(list = ls())



I have added the "rm(list=ls())" on the end to try to reset the workspace because I've found that repeated running of this code can result in different output images. The main problem I am having is that though my values are all between -2.5 and 2.5 the interpolation gives me values well outside that range. Usually shown by colouring the areas white but confirmed by plotting a regular contour map instead of a filled contour. What I'd like to find out is if there is a way to dampen the cubic spline that is being used, or if there is an alternative to interp() that I should be looking at. Like I said before, I'm very new to R, so I may have missed something entirely obvious.

Thanks in advance,
    Craig