Missing line segments in PolarAxis

[pzabka]

When creating lines in PolarAxis, some line segments (around r=0 or theta=2pi) are missing.

MWE:

k = 50
fig = Figure()
ax = PolarAxis(fig[1, 1]; radius_at_origin=0)
lines!(ax, 0:pi/k:2*pi, cos; linewidth=5)
fig

It should be a full circle, but I got this instead:

When changing the parametr k, the effect may vary.

Tested with:
GLMakie v0.10.0 (Makie v0.21.0, Makiecore v0.8.0)
CairoMakie v0.12.0 (Makie v0.21.0, Makiecore v0.8.0)
GLMakie v0.9.10 (Makie v0.20.9, MakieCore v0.7.3)
CairoMakie v0.11.10 (Makie v0.20.9, MakieCore v0.7.3)

[ffreyer]

The gap at r = 0 happens because by default PolarAxis removes points with negative radius. You can turn that off by setting clip_r = false.
The gap at r = 1 happens because the range doesn't include 2pi. With clip_r = false you end up drawing the circle twice you won't see the missing r = 1 section anymore.

[asinghvi17]

Should we clamp r to zero instead of clipping by default? Seems like that would be less surprising.

[jkrumbiegel]

I'm wondering why r = 0 is a negative radius

[ffreyer]

It's not

Makie.jl/src/layouting/transformation.jl

Lines 477 to 479 in d57e9d3

	if trans.clip_r && (r < 0.0)
	return Point2{T}(NaN)
	end

It's just that the next point in the line is at a negative radius.

I think regardless of what we do by default it's going to have some downsides.

• r = max(0, r) modifies user data
• NaN removes data and can lead to missing pieces like here
• keeping r < 0 shows data that in some contexts is invalid and it may not be intuitive where that data ends up

Related:
#3381
#3375

[pzabka]

Thank you for a great explanation.

Out of curiosity, I have tried Plots.jl and Matlab and in both cases the default behaviour is radius_at_origin=0, clip_r = false However, I agree that such a result is quite misleading, and the current Makie behaviour feels better. It is just confusing that the line is not going to r=0, leaving the plot area.

[ffreyer]

Closing this as not-planned. (Unless this becomes a common complaint)