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Is there a way to create a plot in IDL with a color gradient to it? What I'm looking for is similar to this Matlab question. The best I know how to do is to plot each segment of the line in a for loop, but this seems rather cumbersome:

x = float(indgen(11) - 5)
y = x ^ 2

loadct, 2, /silent
!p.background = 255
plot, x, y
for i = 0, 9 do begin
   oplot, x(i:i+1), y(i:i+1), color = i * 20, thick = 4
endfor

enter image description here

I'm using IDL 8.2 if that makes a difference.

DavidH
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2 Answers2

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I had the same issue once and there seems to be no (simple) solution. Though I surrendered, you can try using a RGB-vector and the VERT_COLORS-keywords, provided by the PLOT function:

A vector of indices into the color table for the color of each vertex (plot data point). Alternately, a 3xN byte array containing vertex color values. If the values supplied are not of type byte, they are scaled to the byte range using BYTSCL. If indices are supplied but no colors are provided with the RGB_TABLE property, a default grayscale ramp is used. If a 3xN array of colors is provided, the colors are used directly and the color values provided with RGB_TABLE are ignored. If the number of indices or colors specified is less than the number of vertices, the colors are repeated cyclically.

That would change the appearence more discrete, but maybe it will help you.

sequoia
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    This is exactly what I needed. I've avoided using the plot function in the past in favor of the subroutine, but this works perfectly: `colors = indgen(11) * 20` and `p = plot(x, y, rgb_table = 2, vert_colors = colors`. – DavidH Feb 14 '18 at 13:04
  • At least in my case, I don't necessarily need a smooth gradient because I have so many points to plot, so this stair stepping is fine. – DavidH Feb 14 '18 at 13:11
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I have a routine MG_PLOTS which can do this in direct graphics:

IDL> plot, x, y, /nodata, color=0, background=255
IDL> mg_plots, x, y, color=indgen(10) * 20, thick=4

Of course, it is just a wrapper for what you where doing manually.

Multi-color line

mgalloy
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