On Thursday 11 September 2003 17:09, Alan W. Irwin wrote:
| On 2003-09-11 08:49-0500 Herng-Jeng Jou wrote:
| > BTW, it is my understanding that Plplot constructs contour plot only
| > from gridded data, not from ungridded data.
| That's an easy question to answer. For 5.2.1, plgriddata gives us a
| powerful capability to transform from ungridded data to the gridded data
| required for the PLplot routines that actually plot.
| From the 5.2.1 announcement at
| "plgriddata. Generate grid data for 3D plots from irregularly sampled
| "3D" here should be interpreted in its broadest sense; any plot (contour,
| 3D perspective, shade, 3D shade, etc.) which involves 3D data. plgriddata
| is documented in
|s.20030828/plgriddata.html. One example of its use is given in example 21
| which involves 3D perspective plots and 3D shaded plots, but it should be
| easy to adapt example/c/x21c.c for contoured plots as well.
| We should thank Joao Cardoso for donating the plgriddata code to the
| PLplot project.
plgriddata() uses several algorithms to perform its task. The simplest are
nearest neighbors (KNN) based, and require no additional libraries; the more
sophisticated algorithms uses the csa (cubic spline approximation) and nn
(Natural Neighbours) libraries, both authored by Pavel Sakov
(http://www.marine.csiro.au/~sakov/) and both included in the plplot
distribution. The nn library needs in addition the qhull library, which is
not included in plplot, but it's easy to build and can be obtained at
| Alan W. Irwin
| email: irwin@...
| phone: 250-727-2902
| Astronomical research affiliation with Department of Physics and
| Astronomy, University of Victoria (astrowww.phys.uvic.ca).
| Programming affiliations with the PLplot scientific plotting software
| package (plplot.org), the Yorick front-end to PLplot (yplot.sf.net), the
| Loads of Linux Links project (loll.sf.net), and the Linux Brochure Project
| Linux-powered Science
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