plplot-general

[Plplot-general] filled contour plots with irregular data

[Paul W. B. <pa...@pu...>]

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?

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.)

Thank you very, very much for any hints. And sorry for this quite 
general questions.

Regards
Paul Wellner Bou

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

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

[Paul W. B. <pa...@pu...>]

Hi,

Thanks very, very much for your answer.

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

Yes, I think thats exactly what I want. The "Delaunay Triangulation
Linear Interpolation" method should do a fine job for my case. But I'll
try the cubic spline method, too.

> plshades (or multiple calls to plshade) can generate the actual plot.
> http://plplot.sourceforge.net/docbook-manual/plplot-html-5.9.0/plshades.html

Thank you. I'll have a closer look at plshade this weekend to understand
what this is really doing.

> 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:

No problem. color bar is not the most important thing. Could be drawn
otherwise, too. But thanks for the suggestion.

> 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.

Great. Looks like what I want. I'll try it and report.

Thank you very much.
Paul.

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

[Alan W. I. <ir...@be...>]

On 2008-03-07 14:23+0100 Paul Wellner Bou 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.

There is an octave interface to PLplot that is normally built as part of the
PLplot build.  This interface includes complete access to low-level PLplot
commands (see the octave implementation of all the PLplot standard examples
at bindings/octave/demos/x??c.m) as well as higher-level plotting
functionality (see bindings/octave/demos/p*.m for a a number of examples of
this functionality).  Anyhow, I suggest you try the octave interface to
PLplot since it does have enhanced capabilities, and you do seem to be quite
familiar with Matlab/Octave.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
__________________________

Linux-powered Science
__________________________

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

[Paul W. B. <pa...@pu...>]

Hello,

Thank you for the answer. Yes, I thought about using octave for this. 
The problem is that I was not able to reproduce the Matlab graphs with 
octave, neither using gnuplot nor octplot nor plplot.

And the final application has to be easily installable on windows 
machines, and I don't want to force them to install octave first.

Regards
Paul.