Re: pm3d and parametric function surface plots

[Ethan M. <merritt@u.washington.edu>]

On Thursday 02 December 2004 09:27 am, Johannes Zellner wrote:
> 
> I just thought that coloring parametric surface plots according to the
> computed z-Value is not reasonable or obvious at all.

I agree. 
Then again, I have never needed to plot such a surface at all,
so maybe I am failing to imagine a reasonable use.

> It would be 
> reasonable to color it according to any function which depends on u and
> v (the parametric variables).

Yes, that sounds much more reasonable.  It gives you the same sort
of "4th dimension" that is available for plotting data from a file.
 
>     gnuplot> unset parametric
>     gnuplot> splot f(x, y), color(x, y) w pm3d
> 
> But this time, the specification is ambigous.

I don't like the use of commas at all.
Any syntax that uses commas to mean more than one thing
is intrinsically ambiguous.
By analogy to the existing syntax for data files,
I think the above should instead be

      gnuplot> splot using (x):(y):f(x,y):color(x,y) 

which it may or may not be possible to shorten to

      gnuplot> splot using f(x,y):color(x,y)

> Introducing an option which forces function plots to have a color
> function would solve the ambiguity.

To me it seems more logical to extend "using" to function plots,
and allow explicit assignment of either real or formal parameters
to the various columns.  Since the syntax "splot using ..."
is not currently valid, it will not break existing scripts.

-- 
Ethan A Merritt       merritt@u.washington.edu
Biomolecular Structure Center
Mailstop 357742
University of Washington, Seattle, WA 98195