Re: Contour plots

[Daniel J S. <dan...@ie...>]

Ethan Merritt wrote:

>On Friday 28 January 2005 12:41 am, Hans-Bernhard Broeker wrote:
>  
>
>>*) I'm strictly against any GUI-only feature.  Once we have a suitable
>>command line method of specifying the locus of those contour labels, we 
>>can think of a mouse interaction method of doing the same.  We may even 
>>have to keep in mind that a GUI should be possible while setting up the 
>>command line syntax.  But command line is still *mandatory*.
>>    
>>
>
>I think you are looking at this from the wrong direction.
>A script to label contout plots is not a "GUI-only feature",
>it is an example of a higher-level application you can build
>on top of gnuplot's core functionality.
>  
>

I like the idea, but it seems to me that this is just a tiny step above 
gnuplot.

>I suspect that creating a general contour-labelling algorithm is
>hard enough, and speciallized enough, that it does not belong 
>inside gnuplot.  Instead we should ask ourselves what core functions
>would be needed to allow a higher-level program to be build on top
>of gnuplot. I imagine that to be truly useful, this hypothetical
>program would use a mixture of automated labelling and interactive
>placement or editing.  
>  
>

But any chance of an automated method would need access to the level 
curves generated by the drawing program.  If done outside of gnuplot, 
then there would need to be a first stage of extracting the curves... 
and for that matter, the values associated with the contours would be 
lost to what is built on top of gnuplot... unless of course, it had the 
original data and could reconstruct the level curves... in which case it 
wouldn't need gnuplot's contour functions.

I guess the one strong argument for Gnuplot to be the one to place 
labels would be that without it there is a limitation in the fact that 
Gnuplot's contour plots can't express the level values of the contour in 
black and white.  Grayscale could be used, but that never seems to come 
out looking good.

>The mousing script is an example of how that externally-driven
>interaction may already be supported. I don't know what, if any,
>addition command line options might be needed also. The earlier
>suggestion of letting the user specify a parametric function and
>having gnuplot calculate the intersections with contour lines is
>an interesting start.
>

One of the plots I saw in a dynamics book on the shelf had a nice 
swooping array of labels which makes me think it used a parametric 
function approach.

I'd suspect that some computer science student or group has studied this 
problem.  There must be literature on this problem somewhere.

Dan