Add tag with coordinates to plot in Plots.jl

General Usage
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1

I have a plot with intersecting lines:
plot

And I would like to add a tag or pointer which point to the intersection and display the coordinates of the intersection. Something like this:
tag example

I know the coordinates of the intersection and I know that the function annotate! adds text to the plot. However, I do not know how to add an line or arrow to point to the intersection and how to determine the right position for the text.

2

Here’s the start of a hack if you want one:

plot([(1, 0), (0, 1)]; arrows=true, texts=["hi",""])
3

@gustaphe’s suggestion is good. Just remember that the coordinates are data-relative (not plot display-relative). So zooming in will make the marker bigger.

Alternative using single-point dataset & marker:

You can add the marker as a simple shape that will resize itself when you zoom in. But I don’t see a way to offset the text in a display-relative manner either. Your best bet is probably to specify the alignment of the text as :bottom, :left, or something (see below):

pt = (3,9) #where to place the marker

#Add a single point using marker formatted as desired:
plot!([pt[1]],[pt[2]], markershape=:plus,
	markercolor=:grey, markerstrokecolor=:black, markerstrokewidth=3,
	markersize=10
)

#Annotate with x-value
ptstr = string(pt)
xvalstr = string(pt[1]) #Just x value
annotate!((pt...,text(xvalstr, 14, :bottom, :left, :green)))

image

4

If you don’t need add these markers in an automated fashion, the InspectDR backend allows you to add them using the r and d keys (keyboard).

  • r: reference marker: a single point with (x,y) coords displayed.
  • d: The delta marker: couples with the last reference marker to calculate the distance & slope between them (box can be moved with click+drag).

(more info on mouse/key bindings here:)
→ https://github.com/ma-laforge/InspectDR.jl/blob/master/doc/input_bindings.md

image

Note:

  • The top-left marker is a single marker generated with r while hovering over the plot.
  • The 2 markers on the right were created with the r-d key combination.

Limitation

I don’t think there is an API yet to generate these markers programmatically, but it probably can be added without requiring a much new code (you can open a PR if this interests you).

5

And since you are working with frequency plots, you might be interested in knowing that InspectDR allows you to stack multiple y strips that maintains a common frequency window as you zoom in interactively.

This is ideal for Bode plots (see below)

image
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Limitation

At the moment, this feature does not work with Plots.jl’s linked axes system (only works with stacked y strips; not plots with linked x axes).