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[Octave-bug-tracker] [bug #53397] Delaunay returns inconsistent (cw/ccw)

From: Rik
Subject: [Octave-bug-tracker] [bug #53397] Delaunay returns inconsistent (cw/ccw) orientations in 2-D (needs overhaul)
Date: Mon, 30 Apr 2018 11:07:57 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0

Update of bug #53397 (project octave):

                  Status:                    None => Confirmed              
                 Release:                   4.2.2 => dev                    
                 Summary: Delaunay returns inconsistent (cw/ccw) orientations
in 2d => Delaunay returns inconsistent (cw/ccw) orientations in 2-D (needs


Follow-up Comment #3:

This probably is part of a bigger project.  The implementation of Delaunay is
currently split between the QHull library, the __delaunayn__.cc C++ file, and
delauanayn.m file.

For performance reasons, Octave should delegate as much as possible to QHull. 
It is possible that Octave is simply not giving the correct option to the
QHull API in order to get all clockwise or all counter-clockwise facets.  Or
it may be that Matlab has the same problem and that they implement a
post-processing step after calling QHull in which they weed out zero-volume
facets and re-order all facets to a common direction.

In any case, it would be better for that routine to be done in C++ where for
loops are cheap, rather than in an m-file where they are expensive.

Marking the bug as confirmed, but also adding to the summary that this
requires an overhaul of how Octave implements delauanay.


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