Re: Suggestion for dgrid3d

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

Philipp K. Janert wrote:
> On Wednesday 24 October 2007 12:10, you wrote:
>> 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.
> 
> That's a good point. What kind of things do 
> are you thinking of that depend on the current 
> implementation? 

That's exactly the problem with long-standing de-facto standards --- 
there's no way of knowing if and how people's usage have come to depend 
on it.

We do consider backward compatibility a bit of a holy grail in this 
project.  It's always bad if a change to the program modifies the result 
of a previously established usage.  So new features (like a modified 
weight function) should always be introduced such that they're only 
triggered by commands that would have done nothing useful in earlier 
versions.

> Changing the weight function does not seem to break any existing
> code, as far as I can see.

It's not the code, but it's usage we should be worried about here.

>> 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. 

> Yes, that's true. But I think that's exactly what 
> would be nice to have - to put the ability to 
> control the range into the hands of users, who
> DO know their data! 

I'm afraid you're still thing "filter radius" when you now say "range".
When I say range, I mean the xrange and friends.  That's sufficiently 
controllable by the user.

> For example, if I know that
> my data is very smooth, but not on a grid, I might
> want to use dgrid3d with a small averaging range,
> just to get a surface drawn. But when I know my data 
> to be noisy, I might want to have a wide averaging
> range, to get some of the noise out.

This kind of "range" control is what the power parameter is about.
The higher the power, the more local the filter.  But it's not a range: 
its effect changes with the distribution of input points.