Hi Dieter,

The "sm" (smoothing methods library) of Bowman and Azzalini (Bowman, AW & Azzalini A (1997) Applied Smoothing Techniques for Data Analysis: The Kernel Approach with S-Plus Illustrations, Clarendon Press, Oxford).

Check out pages 9 and 10 (Figure 1.8).

I don't know how large is large for you as a data set, so I can't say how well it goes. I would say it goes as well as anything else.

Rohan Sadler

Dieter Menne wrote:

Dear R-Listers,

I have spatial data on an equidistant rectangular grid, similar to
topographic data. I know that there are quite a few R-packages or base
functions that provide nice iso-contours plot, but I don't want a plot, just
the smoothed isocontour line of ONE level (e.g. 10 mm).

Data sets are large, so it would be preferable if the availability of
regular grid data could be exploited, and the fact that I only need ONE
isocontour line.  Polynomial fits are not adequate, but loess works nicely
for the plots. Akima/interp might be a little too general, and if I remember
Brian Ripley's comments correctly, the coefficients are "only for internal
use".

Can someone suggest me a package?


Dieter Menne


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