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Re: Voronoi Diagrams

From: David Bateman
Subject: Re: Voronoi Diagrams
Date: Mon, 29 Dec 2008 22:53:37 +0100
User-agent: Mozilla-Thunderbird (X11/20081018)

Ryan Matthew Balfanz wrote:
Hi All,
I've changed the the lines starting from line number 127 to the following:
 #idx = find (!infi); # Original
 idx = find ( ! resize (infi, size(c))); # Modified

 ll = length (idx); # Original
 #ll = min (length (idx), length (c)); # Modified
and get strange output.

My input file can be found at
The output can be found at

To get my results do the following in octave:
load inp.dat
voronoi(inp(:,2), inp(:,3))

For the curious, columns 2 and 3 of inp.dat are positional data of
galaxies. I'm having no trouble in MatLab working with this data even
though individual points can be extremely close to one another.

That is a surprising result... It appears that Qhull's Voronoi algorithm has some sort of threshold of whether the distance between a point is considered significant or not that is relative to the distance between two points and the maximum distance between any point. Unfortunately the external box I added to get the matlab compatibiliy works well for convhull and needs to be extremely large in that case to approximate a box at infinite. However, it causes issues for voronoi. For now set scale to something smaller then 1e4 (say scale = 1e2) and it should work.. I'll look at a better fix soon.


David Bateman                                address@hidden
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