bugGNU Octave - Bugs: bug #31760, mesh changes edgecolor...

 
 

bug #31760: mesh changes edgecolor when switching to logarithmic scale

Submitter:  Thorsten Meyer <tmeyier>
Submitted:  Thu 02 Dec 2010 09:27:29 PM UTC
   
 
Category:  Plotting with gnuplot Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Confirmed Assigned to:  None
Originator Name:  Thorsten Meyer Open/Closed:  * Closed
Release:  * dev Operating System:  * GNU/Linux
Fixed Release:  None Planned Release:  None
* Mandatory Fields

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Sat 25 Feb 2012 09:41:05 PM UTC, comment #6: 

I've looked through the gnuplot demos. I can't find any examples where a logscale surface plot is also colored.

I think it a good idea to add a demo with a comment about this so we don't forget.

I'll take care of that.

Ben Abbott <bpabbott>
Group Member
Sat 25 Feb 2012 08:56:16 PM UTC, comment #5: 

Can we close this bug report if the problem is with gnuplot rather than Octave?

If you read in the plot commands directly into gnuplot does the same problem result?

Rik <rik5>
Group administrator
Sat 25 Feb 2012 01:47:44 AM UTC, comment #4: 

I looked at the plot stream for the log and the linear plots. They each contain the Gnuplot commands below.


set xrange [0.000000000000000e+00:1.000000000000000e+01] noreverse;
set yrange [0.000000000000000e+00:1.000000000000000e+01] noreverse;
set zrange [1.000000000000000e+00:1.000000000000000e+02] noreverse;
set cbrange [1:10000];


This looks like a Gnuplot bug to me.

Ben Abbott <bpabbott>
Group Member
Wed 16 Feb 2011 08:57:44 PM UTC, comment #3: 

Hi,

thanks for looking at this.

Just to make sure that we discuss the same thing:
octave with the gnuplot backend produces a nice mesh with linearly graded colors as long as the z-axis is linear (just as octave/fltk and matlab), but switches to monochrome when the z-axis is logarithmic. This happens even if the colorscale is given explicitly by a forth argument to mesh. Try for example:

x = logspace(1,3,30);
y = logspace(1,3,30);
z = y'*x;
mesh (x,y,z, z.^2);
pause
set(gca, "zscale", "log");


Attached is a screenshot of the resulting plot (of the original example below) in matlab (2009b). Matlab produces the same coloring as the fltk backend for me. The coloring stays linearly graded in this case.

From a users perspective: if is isn't possible to get the same color grading with gnuplot, I would prefer to have some color grading instead of none at all.

Thorsten


Thorsten Meyer <tmeyier>
Mon 14 Feb 2011 07:31:12 PM UTC, comment #2: 

Its not clear to me what is the correct behavior in this case. We could use the gnuplot command "set logscale cb" to get the plot colored but I suspect that isn't correct either. Frankly it's not clear to me that the colors already plotted by gnuplot aren't correct for this case. So what does matlab do it this case? Could someone upload a screenshot?

D.

David Bateman <dbateman>
Group Member
Sun 05 Dec 2010 04:56:08 AM UTC, comment #1: 

This bug is confirmed. 

Separately applying the log scale arguments shows that it is only setting the zscale to log which causes the problem.  It is also reversible in that set(gca,"zscale","linear") restores edgecolor.

Rik <rik5>
Group administrator
Thu 02 Dec 2010 09:27:29 PM UTC, original submission:  

was #31779 before savannah went down.

I see this bug on debian testing with gnuplot version 4.4 patchlevel 0, but
not with the fltk backend.

example to reproduce the bug:


x = logspace(1,3,30);
y = logspace(1,3,30);
z = y'*x;

mesh (x,y,z);
pause;
set(gca,  "xscale", "log", "yscale", "log", "zscale", "log");




Thorsten Meyer <tmeyier>

 

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Attached Files
file #22706:  mesh_example.png added by tmeyier (31KiB - image/png)

 

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    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2012-02-25 bpabbott Open/ClosedOpen Closed
    2012-02-25 bpabbott Originator Name Thorsten Meyer
    2011-02-16 tmeyier Attached File- Added mesh_example.png, #22706
    2010-12-05 rik5 StatusNone Confirmed

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