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Re: 3D mesh plotting with a fourth column of data for colouring pm3d

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On Wednesday, July 22, 2015 at 1:55:40 PM UTC-5, Ethan A Merritt wrote:
> javierevergarab@gmail.com wrote:
> 
> > On Wednesday, July 22, 2015 at 12:41:46 PM UTC-5, Javiere wrote:
> >> Dear all.
> >> 
> >> My 3d mesh plotting is currently being colored using gnuplot pm3d.
> >> However the pm3d colours should be related to a variable different from
> >> the z value.
> >> 
> >> It is indicated that (in addition to x,y,z) a fourth column of data
> >> should be used for gnuplot to read RGB color information
> >> (http://www.gnuplotting.org/manpage-gnuplot-4-6/#Q1-1-536).
> >> 
> >> 
> >> Can anybody can let me know how to relate number values with colours?
> > 
> > It clear to me the command required to do the plotting:
> > splot ... using 1:2:3:4 with pm3d lc rgb variable.
> > 
> > I do not know how to relate the 4th column values with RGB colours.
> 
> The 4th column in that case is interpreted as a 24-bit integer
> with containing 8-bit color components (integers 0-255)
> I.e. 
> 
> foo = (Red << 16) + (Green << 8) + (Blue)
> 
> Gnuplot can read hexadecimal numbers, so one possible format for
> the 4th column is
> 
>   0xffffff	# white
>   0xff0000	# pure red
>   0x7f007f	# half intensity magenta
> 
> and so on.
> 
> >> I only recently started using gnuplot and am further constrained by the
> >> fact that gnuplot site is temporarily offline
> >> (http://gnuplot.sourceforge.net/demo/).
> 
> Older copy of relevant demo:
> 
>   http://skuld.bmsc.washington.edu/~merritt/gnuplot/demo_canvas/heatmaps.html
> 
> 	Ethan


Ethan. I appreciate your help.

I have been trying different options and managed to include 3d mesh coloring using a fourth columns including number values using. I am using commands of the form "splot "data.txt" using 1:2:3:6 with lines lt 27"

However I did not find hexadecimal colour representation useful to plot the fading and blending effect of colours of a given palette as can be seen in the demos you sent me. In fact, these graphs use formulas to produce numbers to be translated into corresponding colours of the given palette.

Therefore I decided to work with a fourth column containing number values !?

Worringly, if I try to include a black spot at a particular position on the surface (which i need to do for signaling purposes), the whole surface acquires a colour that corresponds to an extreme of the palette in effect. I assume this is not supported by gnuplot.

Javiere

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3D mesh plotting with a fourth column of data for colouring pm3d Javiere <javierevergarab@gmail.com> - 2015-07-22 10:41 -0700
  Re: 3D mesh plotting with a fourth column of data for colouring pm3d javierevergarab@gmail.com - 2015-07-22 11:03 -0700
    Re: 3D mesh plotting with a fourth column of data for colouring pm3d Ethan A Merritt <sfeam@users.sourceforge.net> - 2015-07-22 11:55 -0700
      Re: 3D mesh plotting with a fourth column of data for colouring pm3d Javiere <javierevergarab@gmail.com> - 2015-07-24 10:11 -0700
        Re: 3D mesh plotting with a fourth column of data for colouring pm3d Ethan A Merritt <EAMerritt@gmail.com> - 2015-07-24 22:54 -0700
          Re: 3D mesh plotting with a fourth column of data for colouring pm3d Javiere <javierevergarab@gmail.com> - 2015-07-28 19:14 -0700

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