# [R] 2D interpolation function

Prof Brian Ripley ripley at stats.ox.ac.uk
Tue May 22 14:25:45 CEST 2001

```On Tue, 22 May 2001, Jim Lemon wrote:

> As part of a project I am doing, I had to present a 2D table as a
> surface.  This was fairly straightforward (using persp), but I needed to
> interpolate points to make it sort of pretty.  This was done by using
> quadratic interpolation between the existing points to smooth out the
> surface a bit.  As I couldn't find an R function that did this, I wrote
> an admittedly nasty pair of functions that will interpolate any
> reasonable number of equally spaced points between the values of an
> object produced by table(), smoothed with any reasonable power function
> of the distance.  In practice, this means I tested it with up to four or
> five interpolated points up to a cubic interpolation.
>
> If anyone is interested in telling me:
>
> a) I overlooked an existing function (p~0.95)

package akima contains functions that will do a better job than
distance-based interpolation. You could also use kriging (spatial,
sgeostat, geoR).

> b) This would be a useful function for them (p~0.01)
>
> I would be happy to hear about it.
>
> Jim
>
> PS - I assumed that the remaining 0.04 would be the probability that no
> one was interested.
>
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--
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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