R: Two dimensional non-parametric regression

Question

What packages and functions in R can perform a two dimensional non-additive local regression/smooth. For example consider

b<-seq(-6*pi,6*pi,length=100)
xy<-expand.grid(b,b) 
x=xy[[1]]
y=xy[[2]]
z= sin(x)+cos(y) + 2*sin(x)*cos(y)
contour(b,b,matrix(z,100,100))

What functions could estimate this?

Answer 1

you can do this with loess:

fit <- loess( z ~ x+ y, span=0.01 )
dev.new()

contour( b, b, matrix( predict(fit), 100, 100 ) )

Answer 2

mgcv has a variety of 2-D spline options.