[manual] suggested addition to pcolor description

[Ben Abbott]

On Feb 3, 2009, at 3:32 AM, Petr Mikulik wrote:

>>> Gnuplot does interpolation in pm3d by splitting each quadrangle  
>>> into smaller
>>> quadrangles. You can try the following example that demonstrates
>>> "shading flat" and "shading interp":
>>>
>>> pcolor([1 2; 3 3])
>>> shading interp
>>> shading flat
>>>
>>> Therefore, I've written the following patch:
>>> https://sourceforge.net/tracker/index.php?func=detail&aid=2558565&group_id=2055&atid=302055
>>> [ 2558565 ] pm3d interpolate 0,0
>>> The animated demo there shows color surface transformations;  
>>> Octave would
>>> use for its "shading interp" the option
>>> 	set pm3d interpolate 0,0
>>
>> I think the attached files look good ... but can you describe what  
>> has been
>> changed.  The results (in your email) look very similar to what the  
>> current
>> gnuplot sources produce.
>
> It is desired to achieve higher resolution plot with an alternative  
> "pm3d
> interpolate" option. Let us suppose that "continuous" colour  
> gradient on the
> map/surface would need edge size of at least 200 pixels on screen  
> window.
> Then
> 	a=hilb(4);
> 	pcolor(a);
> would need
> 	set pm3d interpolate 50,50
> while
> 	a=hilb(100);
> 	pcolor(a);
> would need
> 	set pm3d interpolate 2,2
>
> With the new patch, you can set
> 	set pm3d interpolate -200,-200
> and gnuplot will ensure at least 200 points in both cases, i.e. Octave
> passes the sampling to the drawing backend.
>
> Currently,
> 	set pm3d interpolate 0,0
> is equivalent to 200 points.

Ok, thanks for explaining.

  I'll patch my gnuplot sources and work on a patch for Octave.

Are you looking for some of us to test drive your gnuplot patch, as  
well?

Ben