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[Octave-bug-tracker] [bug #34604] Trivial delaunay throws qhull error
From: |
Rik |
Subject: |
[Octave-bug-tracker] [bug #34604] Trivial delaunay throws qhull error |
Date: |
Thu, 20 Oct 2011 20:23:45 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:5.0) Gecko/20100101 Firefox/5.0 |
Follow-up Comment #5, bug #34604 (project octave):
The error message does appear to be accurate. The center point of the square
is exactly on a facet line (the diagonal from the corners of the square). The
warning message suggests using two options--both of which work for me.
The first option is 'QJ' which "Joggles" the input points. This does
eliminate the exact co-planarity. However, its use isn't particularly
recommended because it reduces the accuracy of the triangulation.
The second option is 'Qz' which adds a point at infinity. This option seems
to work well.
y = [0 1 1 0];
x = [0 0 1 1];
tri = delaunay (x,y, 'Qz')
tri =
4 2 3
4 2 1
Perhaps this option should always be added to low-dimensional data? The
relevant code is in src/__delaunayn__.cc:89.
// default options
if (dim <= 3)
options = "Qt Qbb Qc";
else
options = "Qt Qbb Qc Qx";
Interestingly, I tried the same trial figure in three dimensions, i.e., a unit
cube and delaunay3 fails in exactly the same way. By adding 'Qz' I can get
delaunay3 to pass as well.
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