smoothed contour lines

Hi all,

I'm trying to draw a contour plot
with rounded (smoothed) contour lines instead of sharp angles;
when the grid consists of only a few points
in x- and y- axis, the resulting contour
is in facts rather ugly since very sharp angles may appear.

I did not find any way to do it,
by using either "contour" or "contourplot" (from the lattice package),
I wonder if there exist a way for smoothing the angles,
apart from artificially increasing the grid resolution,