Re: Suggestion for dgrid3d

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Philipp K. Janert wrote:

> Now, the real question is, what are the relative
> advantages for different choices of w(d)?

Well, the primary advantage of the current choice is that it _is_ the 
current choice.  dgrid3d must have been in gnuplot for over a decade 
now.  Changing it now would require careful consideration to ensure 
backward compatibility.

> What
> I am missing most strongly in the current 
> implementation is a way to control the radius 
> over which data points are averaged to form 
> the smooth approximation - control over the
> "band width" of the low pass filter. 

Well, as I said before, there is no such radius, thus nothing to be 
controlled.  OTOH, that's how the algorithm manages to work without 
knowing anything about the data.  I.e. the algorithm is invariant under 
some rescaling of the input.  The surface generated by dgrid3d for

	splot 'data' using ($1*s_xy):($2*s_xy):($3*s_z)

looks the same for any s_xy and s_z (setting aside different choices by 
the autoscaling algorithm).  Only if you scale x and y differently, the 
result changes.  One aspect where this helps is that you don't have to 
adjust the settings for every plot.

Maybe it's the wording in the documentation that's misleading here. 
dgrid3d is a kind of low pass filter, but it's a rather different kind 
than you're used to.  It's sort of an auto-adjusting low-pass filter. 
It has no predefined limiting frequency.