Scale Division in Makie

Specific Domains Visualization
2

One option would be to calculate the data distance covered by some pixel width by listening to ax.finallimits and ax.scene.px_area. Then you can calculate the line and text position in pixel space for the axis scene, and update accordingly. This only works when there’s no axis scale applied.

using DelimitedFiles


volcano = readdlm(Makie.assetpath("volcano.csv"), ',', Float64)


f = Figure()
ax = Axis(f[1, 1])
co = contourf!(volcano, levels = 10, colormap = :Blues)

relpoints = Observable(Point2f[(0, 0), (1, 1)])
label = Observable("label")
width_px = Observable(50.0)
offset_px = Observable(20.0)

linesegments!(ax, relpoints, space = :pixel, color = :black, linewidth = 5)
text!(ax, @lift(($relpoints[1] + $relpoints[2]) * 0.5), space = :pixel, align = (:center, :bottom), text = label, offset = (0, 5))

onany(ax.finallimits, ax.scene.px_area, width_px, offset_px) do lims, pxa, width_px, offset_px
    xmin, xmax = extrema(lims)[1]
    br = Makie.bottomright(pxa) - pxa.origin
    width_data = width_px / widths(pxa)[1] * widths(lims)[1]
    label[] = "$(round(width_data, sigdigits = 3)) km"

    relpoints[] = [
        br + Point2f(-width_px - offset_px, offset_px),
        br + Point2f(-offset_px, offset_px),
    ]
end

notify(ax.finallimits)

f

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