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[Octave-bug-tracker] [bug #50494] griddata loses precision in the linear
From: |
El Colmo |
Subject: |
[Octave-bug-tracker] [bug #50494] griddata loses precision in the linear interpolation of 3 column vectors (using Delaunay triangles) |
Date: |
Wed, 8 Mar 2017 11:48:26 -0500 (EST) |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.75 Safari/537.36 |
URL:
<http://savannah.gnu.org/bugs/?50494>
Summary: griddata loses precision in the linear interpolation
of 3 column vectors (using Delaunay triangles)
Project: GNU Octave
Submitted by: elcolmo
Submitted on: Wed 08 Mar 2017 04:48:24 PM UTC
Category: Octave Function
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: Inaccurate Result
Status: None
Assigned to: None
Originator Name: Colmo
Originator Email:
Open/Closed: Open
Discussion Lock: Any
Release: 4.2.1
Operating System: Any
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Details:
The griddata function loses precision when calculating the linear
interpolation of 3 column vectors (using Delaunay triangles), since only the x
and y parameters are passed to "delaunay" (ie, using the default QHull
options). This results in triangle elimination in "delaunay". When the
generated (reduced) set of triangles is searched by "tsearch", the resultant
interpolated value is less precise than expected.
The fix is trivial - to change the parameters passed to "delaunay", so that
the default QHull options are no longer used, resulting in *no* triangle
elimination by "delaunay", resulting in greatly increased precision of the
interpolated values.
The fix is trivial. In Change the following line (in
"/usr/share/octave/4.0.3/m/geometry/griddata.m", in my deployment) from:
tri = delaunay (x, y);
to either..
tri = delaunay (x, y, {"Qt", "Qc", "Qz"}); #remove default option Qbb, in
order to slightly increase precision (by increasing the triangle count)
or...
tri = delaunay (x, y, {"Qt", "Qbb", "Qc"}); #remove default option Qz, in
order to greatly increase precision (by increasing the triangle count)
Note: this is also an issue in the latest available version of Octave (4.2.1).
_______________________________________________________
Reply to this item at:
<http://savannah.gnu.org/bugs/?50494>
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- [Octave-bug-tracker] [bug #50494] griddata loses precision in the linear interpolation of 3 column vectors (using Delaunay triangles),
El Colmo <=