R help - Mar 2006 - Interpolate univariate data on regular 3D grid to new 3D grid

Dear R Users,

I have some data that is very similar in form to a 3D image - ie univariate
data on a regular 3D grid.  I keep this as a 3D numeric array in R with
attributes describing the sampling points along the 3 dimensions.

I would like to interpolate this onto a new regular 3D grid that I specify
(eg by supplying 3 vectors corresponding to the new grid locations on each
of the 3 dimensions).  Interpolation methods would ideally include nearest
neighbour and linear.

The arrays can be large (> 1e7 points) so I would like this to be efficient.
I can find lots of 1d or 2d interpolation methods but no 3d ones and
anything that I write will probably take me a while to optimise.

Many thanks for any suggestions,

Greg Jefferis.
-- 
Gregory Jefferis, PhD                                   and:
Research Fellow    
Department of Zoology                                   St John's College
University of Cambridge                                 Cambridge
Downing Street                                          CB2 1TP
Cambridge, CB2 3EJ 
United Kingdom

Lab Tel: +44 (0)1223 336683                     Office: +44 (0)1223 339899
Lab Fax: +44 (0)1223 336676

http://www.zoo.cam.ac.uk/zoostaff/jefferis.html           gsxej2 at cam.ac.uk

Package gstat allows 3D interpolation. It doesn't accept
a 3D array directly; you'll have to provide it as

x1 y1 z1 obs1
x2 y2 z2 obs2

etc, e.g. by using expand.grid. Or, you may want to try
out the classes provided by package sp, which allow for
more than 2 dimensions in case of points and grids.
--
Edzer