Re: pcolor and patch

[Ben Abbott]

On Feb 25, 2010, at 12:05 AM, John W. Eaton wrote:

> On 24-Feb-2010, RENOO wrote:
> 
> | This is my first post here as I am starting using Octave and I must confess
> | that I am very happy of the quality of this software so far:clap:
> | 
> | 
> | However, there is one feature I can not make.
> | 
> | I would like to plot my data using a pcolor and then add a patch to hide a
> | part of those data. 
> | I assumed that using the contourf command is equivalent at finding the
> | cordinates of the isoline with the contourc command and then applying the
> | patch command.
> | 
> | So here is a simple example of my script : 
> | 
> | [X,Y,Z] = peaks(50);
> | pcolor(X,Y,Z); shading flat
> | hold on
> | contourf(X,Y,Z,[1 1],'k')
> | 
> | error: patch: property value is missing
> | error: evaluating if command near line 205, column 3
> | error: called from `contourf:parse_args' in file
> | `/usr/share/octave/3.0.5/m/plot/contourf.m'                                 
>                                                
> | error: called from `contourf' in file
> | `/usr/share/octave/3.0.5/m/plot/contourf.m'    
> | 
> | So I tried without any properties : 
> | octave:14> contourf(X,Y,Z,[1 1])                                            
>       
> | error: gnuplot (as of v4.2) only supports 2D filled patches
> | error: evaluating if command near line 537, column 9
> | ....
> | 
> | google ( and the message error ) told me it comes from gnuplot backend. 
> | 
> | So I tried from this  http://old.nabble.com/FLTK-howto--td27703703.html 
> post 
> | 
> | backend("fltk") 
> | 
> | and this leads me to the following error message : 
> | 
> | 
> | octave3.2:3> [X,Y,Z] = peaks(50);
> | octave3.2:4> pcolor(X,Y,Z); shading flat
> | octave3.2:5> hold on
> | octave3.2:6> contourf(X,Y,Z,[1 1],'k')
> | error: mx_el_lt: nonconformant arguments (op1 is 1x2, op2 is 0x0)
> | error: evaluating argument list element number 1
> | error: evaluating argument list element number 1
> | error: called from:
> | error:   /usr/share/octave/3.2.2/m/plot/__contour__.m at line 238, column 15
> | error:   /usr/share/octave/3.2.2/m/plot/__contour__.m at line 188, column 3
> | error:   /usr/share/octave/3.2.2/m/plot/contourf.m at line 73, column 5
> | 
> | I am running octave 
> | octave3.2:6> version
> | ans = 3.2.2
> | 
> | and I also tried with QtOctave version 0.8.1 which runs octave 
> | octave:13> version
> | ans = 3.0.5
> | 
> | but in vain.
> | 
> | Any help  ?
> 
> You can avoid the nonconformant argument error by setting the level
> argument to contourf to be something like [1, 1+eps] instead of [1, 1].
> That's a bug, and I've checked in the following change:
> 
>  http://hg.savannah.gnu.org/hgweb/octave/rev/f074aa6b2c80
> 
> But I don't think gnuplot 4.2 will work for this plot even with this patch:
> 
>  error: gnuplot (as of v4.2) only supports 3D filled triangular patches
>  error: called from:
>  error:   /home/jwe/src/octave/scripts/plot/__go_draw_axes__.m at line 592, 
> column 6
>  error:   /home/jwe/src/octave/scripts/plot/__go_draw_figure__.m at line 102, 
> column 1
>  error:   /home/jwe/src/octave/scripts/plot/gnuplot_drawnow.m at line 99, 
> column 5
> 
> I don't know whether later versions avoid this problem.
> 
> Using the fltk backend with the current sources, I get the first plot
> attached below.  I suspect that is not what you are looking for.
> Using contour instead of contourf, I get the second attached plot.  It
> looks more reasonable, but I'm not sure whether that is the image you
> want.
> 
> BTW, it is best to report bugs to the address@hidden mailing list.
> 
> jwe

The second plot is what I see when I try the example (with contourf) in Matlab.

Ben