gnuplot-beta

[slightly OT] plotting a (pm3d) closed surface with arbitrary vertices

[Dr. J. Z. <joh...@ze...>]

Hello,

forgive me, this is OT, but I guess the guys at this list might be
able to give me help.

I frequently like to splot a (pm3d) surface for which I have arbitrary
x, y, z vertices. The surface is usually well-behaved in a sense that
it's smooth, w/o singularities and has only long-range (low frequency)
changes.

As first approximation -- and this is the best I have -- I use 'splot
with points' using 'linetype pal' to get colors and I use pretty large
point sizes to get part of the surface "covered".

Any ideas how to get a real closed surface? -- I guess I'd need
something like a function which searches the closest vertices (in x, y)
and then connects the vertices by triangular surfaces.

Any hints much appreciated.

-- 
Johannes

Re: [slightly OT] plotting a (pm3d) closed surface with arbitrary vertices

[<HBB...@t-...>]

Dr. Johannes Zellner wrote:
> Any ideas how to get a real closed surface? -- I guess I'd need
> something like a function which searches the closest vertices (in x, y)
> and then connects the vertices by triangular surfaces.

What you're looking for is (a variation of) 'set dgrid3d'.  I'm slightly 
worried you didn't manage to find that in the documentation by yourself.

Re: [slightly OT] plotting a (pm3d) closed surface with arbitrary vertices

[Dr. J. Z. <joh...@ze...>]

Hans-Bernhard,

Thanks!
This was indeed what I was looking for and it works already pretty well.
What I'd need now, is to invalidate the data outside some distance to
the data points. Suppose I've data whithin a banana shape in x, y and
like to have colored pm3d rectangles only when x, y are near the banana
(which is defined by the scatter x, y data points).
Maybe you've a quick solution for this problem as well? ;-)

-- 
Johannes

On Tue, Mar 06, 2007 at 10:36:00PM +0100, Hans-Bernhard Bröker wrote:
> Dr. Johannes Zellner wrote:
> > Any ideas how to get a real closed surface? -- I guess I'd need
> > something like a function which searches the closest vertices (in x, y)
> > and then connects the vertices by triangular surfaces.
> 
> What you're looking for is (a variation of) 'set dgrid3d'.  I'm slightly 
> worried you didn't manage to find that in the documentation by yourself.
> 
> 
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Re: [slightly OT] plotting a (pm3d) closed surface with arbitrary vertices

[<HBB...@t-...>]

Dr. Johannes Zellner wrote:

> What I'd need now, is to invalidate the data outside some distance to
> the data points. 

Sorry, no can do.  You must have seen me state this before: gnuplot is a 
plotting program, not a general-purpose number crunching engine.  There 
are limits to what it'll do, and you've just hit one.

 > Suppose I've data whithin a banana shape in x, y and
> like to have colored pm3d rectangles only when x, y are near the banana
> (which is defined by the scatter x, y data points).

In its general case it's already a surprisingly tricky task to come up 
with a usable formal definition of such "banana shapes" that computers 
can test, much less generate by themselves.