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

[Ross Ihaka]

> From: Bill Simpson <wsimpson at uwinnipeg.ca>
> Subject: Re: contour labelling [was "Re: [R] image ()"]
> MIME-Version: 1.0
> 
> > We may be missing the crux here: was it to have a means of
> > displaying such surfaces?
> 
> Yes, bang on. I knew of the
> existence of the Delaunay code in the R libraries. Yes I want
> to make a picture that places a planar facet on each triangle.
> The resulting surface looks like the surface of a cut diamond
> for example (assuming the cuts give triangular facets). So far
> as I know there is no way to display such a 3D plot in R. persp
> uses rectangular rather than triangular mesh.

Once the trianglation was produced it would be just a minor change in
the present "persp" function to plot it.  The algorithm I use is to
sort the facets by depth and then to plot them, back to front.  This
works just as well for triangular facets as rectangular ones.

If you'd care to define some data structures (or better yet a class)
which will hold a desciption of the triangulation, I can have my student
tweak the present code to display the structure.

	Ross
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