Octaviz help, general question about plotting scattered data

[Jordi Gutiérrez Hermoso]

Jordinian Productions, in collaboration with VTK and mplayer studios,
brings you Octave: The Movie

    http://platinum.linux.pl/~jordi/movies/radial.ogg
    http://platinum.linux.pl/~jordi/movies/nonradial.ogg

(Ogg Theora. If you have problems viewing it, try VLC or installing
the Theora codecs for your operating system. If someone knows of an
easy way to stitch 1000 frames of animation into an animated gif using
free software, do let me know. I tried with imagemagick's convert, but
it made my computer thrash. I also tried mplayer, which makes it look
rather ugly, since it's only in 256 colours.)

Now, I have a problem with the colour scale, using Octaviz. For a
movie, it would be nice if I could do something absolute like, "height
0.25 always means orange" and "height -0.4 is always violet". In
short, I need more control over Octaviz's colour scale. Can this be
done? I'm sure it can be done with a quick source hack, but can
someone point me in the right direction?

My second question is no doubt more complex. Suppose I have scattered
data points on some unstructured grid on the plane, and I have a
function value at each point. That is, the only data I have is a bunch
of (x,y,z) triplets that can be given to me in any order. They should
represent samplings from a smooth function, hopefully a solution to a
shallow water equation without shocks, once I get my code working. How
can I form a quasi-smooth surface which interpolates with small
polygons the data points that I give? I realise this may be a bit of a
complicated problem in computational geometry, but it also seems like
it should be a problem common enough for someone to have solved it
very well already.

Thanks!
- Jordi G. H.