[Gnuplot-info] Data matrix plot with not valid grid points

[Seoane A. T. <ts...@e-...>]

Hello!

I have a problem, long to explain, but not complex to understand:

I am trying to plot with image a data matrix with the following
properties:
- The valid data goes from 0 to 1.
- There exist invalid data, which has a z value of 2.
- The palette range will be [0:0.01]

I want 29 colors to be used in the palette, and so, I use this script:

set cbrange [0:0.01]
set palette model RGB defined ( 0 "#8b0000", 1 "#8b0000", 1 "#a80000", 2
"#a80000", 2 "#c50000", 3 "#c50000", 3 "#e20000", 4 "#e20000", 4
"#ff0000", 5 "#ff0000", 5 "#ff2900", 6 "#ff2900", 6 "#ff5300", 7
"#ff5300", 7 "#ff7c00", 8 "#ff7c00", 8 "#ffa500", 9 "#ffa500", 9
"#ffbc00", 10 "#ffbc00", 10 "#ffd200", 11 "#ffd200", 11 "#ffe900", 12
"#ffe900", 12 "#ffff00", 13 "#ffff00", 13 "#bfff00", 14 "#bfff00", 14
"#7fff00", 15 "#7fff00", 15 "#40ff00", 16 "#40ff00", 16 "#00ff00", 17
"#00ff00", 17 "#00ff40", 18 "#00ff40", 18 "#00ff80", 19 "#00ff80", 19
"#00ffbf", 20 "#00ffbf", 20 "#00ffff", 21 "#00ffff", 21 "#00bfff", 22
"#00bfff", 22 "#0080ff", 23 "#0080ff", 23 "#0040ff", 24 "#0040ff", 24
"#0000ff", 25 "#0000ff", 25 "#0000e2", 26 "#0000e2", 26 "#0000c5", 27
"#0000c5", 27 "#0000a8", 28 "#0000a8", 28 "#00008b", 29 "#00008b" )
set view map
splot 'matrix.txt' with image

With this script, all the valid data from 0.01 to 1 will have the last
color of the palette, which is OK, but the invalid data will have that
color too, but I would like those data points to have another color. Is
there any simple way to achieve this, like skipping the points with
certain z values?

As I could not find a simple solution, I have tried the next more or
less complex approach which "almost" works:
- Redefine the palette range to include the invalid data.
- Redefine the palette with its real range values to have the same
colors than before for the same values.

set cbrange [0:2]
set palette model RGB defined ( a "#8b0000", b "#8b0000", b "#a80000", c
"#a80000", c "#c50000", d "#c50000", d "#e20000", e "#e20000", e
"#ff0000", f "#ff0000", f "#ff2900", g "#ff2900", g "#ff5300", h
"#ff5300", h "#ff7c00", i "#ff7c00", i "#ffa500", j "#ffa500", j
"#ffbc00", k "#ffbc00", k "#ffd200", l "#ffd200", l "#ffe900", m
"#ffe900", m "#ffff00", n "#ffff00", n "#bfff00", o "#bfff00", o
"#7fff00", p "#7fff00", p "#40ff00", q "#40ff00", q "#00ff00", r
"#00ff00", r "#00ff40", s "#00ff40", s "#00ff80", t "#00ff80", t
"#00ffbf", u "#00ffbf", u "#00ffff", v "#00ffff", v "#00bfff", w
"#00bfff", w "#0080ff", x "#0080ff", x "#0040ff", y "#0040ff", y
"#0000ff", z "#0000ff", z "#0000e2", a1 "#0000e2", a1 "#0000c5", b1
"#0000c5", b1 "#0000a8", c1 "#0000a8", c1 "#00008b",1 .1 "#00008b", 1.1
"#bebebe", 2 "#bebebe" )
set view map
splot 'matrix.txt' with image

Where the parameters "a" to "c1" has the next value:
0. + 0.01 * i / 29.
i=0, 1, 2, ...

The problem with this is that not all colors are used, but I have found
that if the palette range is smaller, it works OK, so maybe is a gnuplot
bug or limitation. Anyway, I cannot do the range smaller, as there would
be valid data with the color of invalid data (in the example there is no
valid data from 0.01 to 1, so it is perfect, but not always will be this
way).
This would be the script for the limited range that works:

set cbrange [0:.05]
set palette model RGB defined ( a "#8b0000", b "#8b0000", b "#a80000", c
"#a80000", c "#c50000", d "#c50000", d "#e20000", e "#e20000", e
"#ff0000", f "#ff0000", f "#ff2900", g "#ff2900", g "#ff5300", h
"#ff5300", h "#ff7c00", i "#ff7c00", i "#ffa500", j "#ffa500", j
"#ffbc00", k "#ffbc00", k "#ffd200", l "#ffd200", l "#ffe900", m
"#ffe900", m "#ffff00", n "#ffff00", n "#bfff00", o "#bfff00", o
"#7fff00", p "#7fff00", p "#40ff00", q "#40ff00", q "#00ff00", r
"#00ff00", r "#00ff40", s "#00ff40", s "#00ff80", t "#00ff80", t
"#00ffbf", u "#00ffbf", u "#00ffff", v "#00ffff", v "#00bfff", w
"#00bfff", w "#0080ff", x "#0080ff", x "#0040ff", y "#0040ff", y
"#0000ff", z "#0000ff", z "#0000e2", a1 "#0000e2", a1 "#0000c5", b1
"#0000c5", b1 "#0000a8", c1 "#0000a8", c1 "#00008b", .03 "#00008b", .03
"#bebebe", .05 "#bebebe" )
set view map
splot 'matrix.txt' with image

I would be very grateful if anyone could give me a solution!

I have attached 3 images for the 3 scripts so you can see the problem.

Thanks!

Teodoro Seoane



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