[R] 3D density estimation

[Chris Knight]

I am trying to carry out density estimation for three dimensions 
(with anywhere between a few hundred and ~8000 data points). Which 
leads me to ask:

a) is there any equivalent to kde2d (in MASS) or bkde2D (in 
KernSmooth) out there for three dimensions?

b) if not, my skills only seem to extend as far as writing a function 
which measures density as the number of data points falling within a 
sphere at each point on a 3D grid. The results for  spheres of the 
minimum size to cover all the space (i.e. slightly intersecting) on a 
30x30x30 mesh don't seem too bad.
  i) How inadequate is such an analysis likely to be for subsequent 
comparison of different density distributions?
ii) Is there anything equally simple I could implement which might be 
preferable?

Any help much appreciated,

Chris
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Dr. Christopher G. Knight               Tel:+44 (0)1865 275 111
Department of Plant Sciences              +44 (0)1865 275 790
South Parks Road
Oxford          OX1 3RB
UK                                                                 ` 
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