# [ncl-talk] What is the spatial interpolation method used by "contouring 1-D data"?

Wenshan Wang wenshanw at uci.edu
Wed Oct 10 17:04:27 MDT 2018

```Hi Dennis,

I am so sorry for the delay. I was traveling.

What I tried to understand is the following description of contour1d_1.ncl
on the webpage 'Contouring one-dimensional X, Y, Z (random) data' (
https://www.ncl.ucar.edu/Applications/contour1d.shtml):
"By default, NCL will generate smoothed contours (see first frame) in an
area enclosed by a convex hull  <https://en.wikipedia.org/wiki/Convex_hull>of
the data".

Based on the links you included and a little digging into the NCL code, is
it safe to say that:
1, the smoothing method is: cubic spline interpolation
2, the convex hulls are created using the Delaunay triangulation (the dual
of Voronoi diagram) by calling 'triangle'?
But I didn't find the actual calling commands in NCL code.

Best,
Wenshan
------------------------------------------------------------------------------
Post-doctoral Scholar
Zender Research Group
Department of Earth System Science
University of California, Irvine

On Sun, Sep 16, 2018 at 3:14 PM Dennis Shea <shea at ucar.edu> wrote:

> Without going into the code, a guess would be:
> *http://ngwww.ucar.edu/supplements/conpack/#Intro2DSmoothing*
> <http://ngwww.ucar.edu/supplements/conpack/#Intro2DSmoothing>
> *http://ngwww.ucar.edu/supplements/dashpack/*
> <http://ngwww.ucar.edu/supplements/dashpack/>
> Correct:  it is not "simple 9-point smoothing"
> ====
> Not sure what you mean by: "Triangulated irregular networks"
>
> * http://www.cs.cmu.edu/~quake/triangle.
> <http://www.cs.cmu.edu/~quake/triangle.html>html
> <http://www.cs.cmu.edu/~quake/triangle.html>*
> <http://www.cs.cmu.edu/~quake/triangle.html>
>
>
>
> *https://www.ncl.ucar.edu/Document/Graphics/contour_grids.shtml
> <https://www.ncl.ucar.edu/Document/Graphics/contour_grids.shtml>*
>
>
> <http://www.cs.cmu.edu/~quake/triangle.html>
>
>
> On Wed, Sep 12, 2018 at 4:16 PM, Wenshan Wang <wenshanw at uci.edu> wrote:
>
>> Hi NCL-talk,
>>
>> What is the spatial interpolation method used in this example
>> contour1d_1.ncl?
>> Is it "Triangulated irregular networks"?
>> Where can I find a more detailed description?
>>
>> Also, what is the smoothing method here?
>> seems not a simple 9-point smoothing.
>>
>> Thank you!
>>
>> Best,
>> Wenshan
>>
>> ------------------------------------------------------------------------------
>> Post-doctoral Scholar
>> Zender Research Group
>> Department of Earth System Science
>> University of California, Irvine
>>
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>
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