From help-octave-request at bevo dot che dot wisc dot edu Fri Feb  7 12:05:17 2003
Subject: Re: 3d plotting, griddata and deluanayn
From: =?iso-8859-1?q?Jo=E3o=20Cardoso?= <jcard at fe dot up dot pt>
To: help-octave at bevo dot che dot wisc dot edu
Date: Fri, 7 Feb 2003 17:03:02 +0000

On Friday 07 February 2003 16:20, Paul Kienzle wrote:
| Joćo Cardoso wrote:
| >On Tuesday 04 February 2003 02:28, Paul Kienzle wrote:
| >| If you are on Windows, you will need to first figure out how to
| >| compile qhull for Windows.  We haven't done so yet.
|
| I should add that under the most recent cygwin and the next mingw,
| there is no reason it shouldn't build and be usable even as a DLL.
| If nothing else, static linking should be possible.
|
| >| If you are on unix, follow the octave-forge/main/geometry/readme
| >| instructions
| >| for installing qhull.  I haven't tried yet with the most recent
| >| qhull release.
| >|
| >| Download the correct version of octave-forge (octave.sf.net) for
| >| your particular
| >| version of octave (the latest is for octave 2.1.40 I believe ---
| >| if you are using
| >| something more recent, you will need to get the CVS version).
| >|
| >|     ./configure
| >|     make
| >|     make install
| >|
| >| griddata does not work as quickly as I would like.  Talk to the
| >| qhull author about how to improve it if it is not fast enough for
| >| you.
| >
| >I don't think that Qhull is slow, slow is the searching of triangles
| > in tsearch.
|
| Agreed.  Time permitting, I understand the author of qhull is
| interested in having griddata
| functionality in qhull.  Please let him know what you are doing.
|
| >I'm using Sakov's "nn" (natural neighbors) library
| >http://www.marine.csiro.au/~sakov/ that uses Lawson's "walking
| >triangle" algorithm to search for a triangle given a point. "nn"
| > uses "triangle", which not free software, but I have adapted it to
| > work with Qhull.
|
| Oops --- Andreas is using triangle in his FEM stuff.  Your are right
| --- the license is not
| open source since it does not allow redistribution for commercial
| purposes.  Does
| triangle do anything that qhull doesn't?

triangle uses exact arithmetic, while Qhull uses floating point; because 
of this triangle might be more robust on certain datasets.
triangle does constrained triangulation, which Qhull does not. This is 
not required when gridding for plotting.

| >plgriddata() will soon be integrated into PLplot.
|
| Any chance you could create 'griddata' which we could include in
| octave-forge
| and call that from plgriddata?

It's the other way around, plgriddata() is (will be) a PLplot API, and 
the motivation of its writing was to have a griddata.m in 
plplot_octave, for plotting purposes.

plgriddata() by itself is mostly self-contained and with minor 
modifications it can be built outside PLplot, but it needs two external 
libraries, csa and nn, both written by Sakov, and one of them needs to 
be patched to work with Qhull.

But Sakov's libraries have simple programs that exercise the libraries 
and can read sample points from data files and write gridded data to 
output files, so its easy to embed these programs in an Octave script. 
Writing/reading large data files will be slow, though.

Joao

|
| Thanks in advance,
|
| Paul Kienzle
| pkienzle at users dot sf dot net
|
|
|
|
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