contour labelling [was "Re: [R] image ()"]

Prof Brian D Ripley ripley at
Fri Dec 4 19:15:45 CET 1998

On Fri, 4 Dec 1998, Thomas Lumley wrote:

> On Thu, 3 Dec 1998, Bill Simpson wrote:
> > > include upgrading contour, image, persp etc.  In addition I hope that
> > > he will also add some mapping facilities along the lines of GMT (using
> > > their shoreline database).
> > > 
> > > Now would be a good time to make suggestions about desirable features.
> > 
> > OK this may be a long shot.
> > I often have to make a plot of like this: the heights (z) of trees in a
> > forest (whose locations are unif rand x,y) are recorded. Now we make a 3D
> > shaded surface plot of the (x,y,z) data. A triangular mesh is made by
> > finding the Delaunay triangulation (nearest neighbours are connected).
> > 
> > I am not talking about doing some form of interpolation (hence forcing the
> > data onto a regular grid).
> There is GPLed Delaunay triangulation code in Java (including a fast
> approximate algorithm) as part of Visad
> ( There is an old C
> implementation which may well have the same algorithms.

There is Delaunay code in the R package tripack, and, implicitly, in
package akima which may well be helpful: if I understand Bill
correctly he wants to put a plane on each triangle to get a surface (which
is interpolation) and Akima was more sophisticated and used quintics
to achieve a smooth interpolated surface. We may be missing the crux
here: was it to have a means of displaying such surfaces?

Brian D. Ripley,                  ripley at
Professor of Applied Statistics,
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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