# bug #49774: convhull doesn't accept option simplify

 Submitter: Juan Pablo Carbajal Submitted: Tue 06 Dec 2016 01:09:40 AM UTC Category: Octave Function Severity: 3 - Normal Priority: 5 - Normal Item Group: Matlab Compatibility Status: Confirmed Assigned to: None Originator Name: jpi Open/Closed:  * Open Release:  * dev Operating System:  * Any Fixed Release: None Planned Release: None
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## Discussion

Tue 13 Nov 2018 02:26:53 AM UTC, comment #4:

I've only been looking at this today, but that said, I'm not sure if simplify is not extraneous.  Small experimentation with qhull gets me a set of random points in a square with

rbox 50 D2 | qconvex G > a

In this case the interior points are not displayed in geomview.  To display the interior and as I understand it simplified points we need to run qconvex Ga instead of G.  This shows all the points in the interior of the convex hull and the hull itself.  My question is if the default behaviour in qhull is to make the convex hull and ignore the interior points, what is simplified by simplify?

That said, I'm sure mathworks doesn't put things like simplify in their code without reason.

Chris Gorman <chrisgorman>
Sun 11 Dec 2016 09:57:42 PM UTC, comment #3:

In the script from comment #1, ks=k.

You can see the behavior of "simplify"= true in the script

xx = -3:1:3;
yy = -3:1:3;
[x,y] = meshgrid(xx,yy);
k = convhull(x,y);
ks = convhull(x,y, 'simplify', true);
save chull1.mat

chull1.mat attached,

Note that 'simplify'= true omits all the points that if we drop them, the convex hull will not change.
In the 2D case it's simple:
if a few points are on a straight segment, the inner points are
omitted, and the end points are left.

(file #39198)

Avinoam Kalma <avinoam>
Fri 09 Dec 2016 03:08:05 PM UTC, comment #2:

@Juan: Can you try the example in comment #1 and report back.  I can't implement the feature until I know what it's supposed to do.

Rik <rik5>
Tue 06 Dec 2016 05:02:28 PM UTC, comment #1:

Could you run the sample script in Matlab and upload the results so we can see what the "simplify" option does?

xx = -1:.05:1;
yy = abs(sqrt(xx));
[x,y] = pol2cart(xx,yy);
k = convhull(x,y);
ks = convhull(x,y, 'simplify', true);
save chull.mat

Rik <rik5>
Tue 06 Dec 2016 01:09:40 AM UTC, original submission:

Option 'simplify' is not accepted. Couldn't find the equivalent for qhull

https://ch.mathworks.com/help/matlab/ref/convhull.html
http://www.qhull.org/html/qh-quick.htm#options

Juan Pablo Carbajal <juanpi>

## Attached Files

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Attached Files
file #39198:  chull1.mat added by avinoam (488B - application/octet-stream)

## Dependencies

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