Logarithmic colorbar for multiple colored plots

Specific Domains Visualization
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1

Hi,

I have a series of plots, each associated with a different value of a parameter called k. The idea was to plot each line with a different color from a colormap and have the colorbar indicate which value of k each plot is associated with, rather than using a legend. The plots are created by a loop, creating one plot per iteration.

I’m quite happy I found the parameter line_z, which automatically creates a colorbar and assigns the right color to the plot, rather than having to create both of them seperately, as suggested in some places on the internet.

However, the parameter k is exponentially spaced (from 5 to 500, so 50 is the midpoint) so I need logarithmic scaling.

colorbar_scale=:log10 seems to do that for the colorbar just fine, but the plots don’t follow, so the colors don’t match. I suppose one option would be to take the log of k instead and change the tick labels, but I haven’t figured out how to change tick labels and that also seems like an ugly workaround for something that should work out of the box. Setting zscale=:log10 just prints a warning No strict ticks found.

I’m using this before the loop:

using Plots
plot(xlabel="\$L_v\$ (pu)", ylabel="frequency (Hz)", colorbar_title="k")

This at the end of the loop

plot!(x, y, seriescolor=:roma, line_z = k, label="", colorbar_scale=:log10)

and somehow I still need to run plot!() after the loop for the plot to actually show up, I’m not quite sure why.
This is without the parameter colorbar_scale, plot colors and colorbar locations match, but you can’t tell the first 2 plots apart, because they have almost the same color:
plot_23

This is with the parameter colorbar_scale, the colorbar looks fine, but the plots don’t look any different and thus no longer match the values indicated by the colorbar
plot_22

Taking the log10 of k gives me correct plot colors, but the colorbar scale if obviously wrong:
plot_24

I was thinking I could use the latter and modify the tick labels, but I haven’t figured out how to do that and I also think that I should not need to do this - the correct color scaling should work out of the box.

My problem seems very similar to what is discussed in this issue, but it says the issue is solved and I don’t really know how to transfer the workarounds to my problem without major changes to the plotting code.

2

The link provided suggests the issue is solved in CairoMakie and PythonPlot, but not in Plots?

3

Yeah, that seems to be the case, also the issue is filed with Makie. I’m still a bit confused about the different Plotting options in Julia. Should I file an issue with Plots?

4

There is probably already an issue about this in Plots.jl, but please do some searching before opening a new one.

It affects the gr() backend, but not e.g. pythonplot().

Simple test code:

using Plots; pythonplot(dpi=100)

x = [0, 1]
y = [i*x for i in 1:5]
z = [10^i for i in 1:5]

p = plot()
foreach(i->plot!(x, y[i], c=:jet, line_z=z[i], label="", colorbar_scale=:log10), 1:5)
p
1 Like
5

Not if we define the plot keyword argument colorbar_title as: colorbar_title="log10(k)"