Re: Gnuplot logarithmic contours and palette

[Aapo L. <aap...@gm...>]

On Tue, 2005-03-22 at 21:15 +0200, Aapo Lankinen wrote:
> Hi!
> 
> I noticed something strange using Gnuplot 4.1 CVS (and Gnuplot 4.0,
> too): the following commands
> 
> ---- clip ----
> unset surface
> set contour
> set logscale z
> set palette model HSV functions gray, gray, 1.0-0.5*gray
> set log cb
> unset colorbox
> set cntrparam levels 30
> set view 0,0
> splot x**2+y**2+1.0 palette
> ---- clap ----
> 
> draw nice coloured contours as you would expect, but the the contour
> labels in the legend are of wrong colour - all the contour label lines
> in the legend have the same colour as the maximum intensity contour
> line.  However, the contour label numerical values seem to be correct in
> the legend.  This happens with at least x11 and postscript terminals.
> I'm using Debian i386 GNU/Linux (Sarge).  Can someone confirm?


Nevermind, I figured it out myself.  In the logarithmic mode of the
contour PM3D-plot there is two subsequent log10():s of the z-coordinate
of the legend, which effectively renders the legend line samples to the
same colour.  I removed the other de-log, and following patch fixes the
problem at least for me.  :-)  I hope it does not cause any other
unexpected problems.  Can someone check if it's safe?  I don't know
anything about Gnuplot except reading the source for an hour :-)
Maybe someone could perhaps apply it to the CVS, if it indeed does work
for others?  (diff for contour.c below and attached)

                                                        Aapo





--- contour.c   2005-03-22 22:07:26.589004130 +0200
+++ contour.c   2005-03-22 22:08:12.726777705 +0200
@@ -247,7 +247,7 @@
            contour_list->isNewLevel = 1;
            sprintf(contour_list->label, contour_format,
AXIS_DE_LOG_VALUE(FIRST_Z_AXIS,z));
 #ifdef PM3D
-           contour_list->z = AXIS_DE_LOG_VALUE(FIRST_Z_AXIS, z);
+           contour_list->z = z;
 #endif
        }
     }




-- 
Aapo Lankinen <aap...@gm...>