Re: [Matplotlib-users] Contouring a large set of ungridded data

[Jeff W. <js...@fa...>]

John Hunter wrote:
>>>>>> "Robert" == Robert Kern <rk...@uc...> writes:
>>>>>>             
>
>     Robert> In any case, natgrid isn't Delaunay triangulation, but
>     Robert> natural neighbors interpolation which is better (and
>     Robert> probably state of the art for these kinds of graphics). It
>     Robert> might be easiest to contact Dave Watson and ask if we can
>     Robert> distribute his code in matplotlib under matplotlib's
>     Robert> license.  I can't find any contact information for him,
>     Robert> however.
>
> I'm all for this but am not optimistic.  It's my understanding that
> the NCAR folks are under a fairly heavy legal burden.  Jeff: could you
> spearhead this effort and see if there is any interest on their part
> in relicensing their griddata code under a more permissive license?
>
> JDH
>
>   

John:  I will do this and let you know.  I agree with Robert on qhull - 
it's not the way to go.  I did find this however:

http://www.marine.csiro.au/~sakov/

Bivariate spline-based techniques offer robust and efficient 
approximation solutions. Here `csa' (standing for "cubic spline 
approximation") is a small library for approximating 2D irregular 
(scattered) data with bivariate C1-continuous cubic splines 
<http://www.math.uni-mannheim.de/%7Elsmath4/paper/VIS2001.pdf.gz>. For 
uniformly distributed data this algorithm is clearly superior than 
Natural Neighbours interpolation: it is faster (O(n)!), more robust 
(approximation, not interpolation) and better performing (C1!). (But 
take care when dealing with clustered data.) From version 1.09, `csa' 
can take advantage of the known variance of the data.

The LICENSE reads:

Bivariate Cubic Spline approximation library + standalone utility
Version 1.14

Copyright 2002 CSIRO Marine Research
GPO 1538 Hobart
TAS 7001
Australia
Please send comments and bugs to Pav...@cs...

There is no warranty whatsoever.  Use at your own risk.

These code may be freely redistributed under the condition that the 
copyright
notices are not removed. You may distribute modified versions of this code
UNDER THE CONDITION THAT THIS CODE AND ANY MODIFICATIONS MADE TO IT IN THE
SAME FILE REMAIN UNDER COPYRIGHT OF CSIRO, BOTH SOURCE AND OBJECT CODE ARE
MADE FREELY AVAILABLE WITHOUT CHARGE, AND CLEAR NOTICE IS GIVEN OF THE
MODIFICATIONS.

If this sounds OK I'll investigate further.

-Jeff


-- 
Jeffrey S. Whitaker         Phone : (303)497-6313
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