Re: [Plplot-general] filled contour plots with irregular data

[Hezekiah M. C. <hc...@at...>]

On Fri, Mar 7, 2008 at 8:23 AM, Paul Wellner Bou <pa...@pu...> wrote:
> Hello,
>
>  i am writing a program in C++ where I am implementing the stuff I
>  developed my thesis about eye glass optics with Matlab/Octave. I tried a
>  C++ interface to gnuplot, but as the interface is not very nice and as I
>  did not find this feature there until now, I am trying the C++ PLPlot
>  interface right now.
>
>  I need to draw graphs like those: http://m21s26.vlinux.de/math/gsg.png
>
>  The data does not fit in a regular grid, so there has to be a kind of
>  triangulation or something similar. In Matlab I use the function
>  griddata for this. The lines to draw this graphs in Matlab are following:
>
>  lmin = min(min(Zi));
>  lmax = max(max(Zi));
>  levels=[lmin:min(.1,(lmax-lmin)/100):lmax];
>  [C,h] = contourf(Xi,Yi,Zi,levels,'LineStyle','none');
>  axis equal;
>  colorbar;
>  grid on;
>
>  Is there a way to do this with PLPlot? And if there is, how? Is this
>  possible with the plstream::fcont method? Does PLPlot implement some
>  kind of triangulation or do I have to write this on my own?

Would plgriddata do what you need?
http://plplot.sourceforge.net/docbook-manual/plplot-html-5.9.0/plgriddata.html

PLplot comes with several gridding methods, and I have used it for a
few simple tests.

plshades (or multiple calls to plshade) can generate the actual plot.
http://plplot.sourceforge.net/docbook-manual/plplot-html-5.9.0/plshades.html
PLplot does not have a built-in function to draw a color bar.  I have
written a simple one in OCaml which can probably be translated to
C/C++ without a lot of trouble:
http://code.google.com/p/ocaml-plplot/source/browse/trunk/extras.ml -
color_bar at line 77 uses color map 1 (continuous colors) and
color_bar0 at line 137 uses color map 0 (indexed colors).  The OCaml
plplot functions follow the C functions pretty closely.

This is an example of what a color_bar0 color bar looks like:
http://www.atmos.umd.edu/~hcarty/precip_maps/August/trmm_august_climatology.png
color_bar would be similar.

>  Another issue: Is there a way to draw "quiver" graphs like this one?
>  http://m21s26.vlinux.de/math/achs.png
>  (In this case I multiplied the arrow length of the points with the z value.)

I think plvect will do what you want here.
http://plplot.sourceforge.net/docbook-manual/plplot-html-5.9.0/plvect.html
plsvect can change the arrow style, and will hopefully give you what you want.

I am new to PLplot as well, so these may not be the best methods
available.  They should help with what you need though.

Hez

-- 
Hezekiah M. Carty
Graduate Research Assistant
University of Maryland
Department of Atmospheric and Oceanic Science