Makie.jl: Feature request: heatmap that can handle irregular rectilinear grids

[briochemc]

MWE:

x = tan.(atan(-3):0.1:atan(3))
y = -2.5:0.1:2.5
peaks(x,y) = 3*(1-x)^2 * exp(-(x^2) - (y+1)^2) - 10*(x/5 - x^3 - y^5) * exp(-x^2-y^2) - 1/3*exp(-(x+1)^2 - y^2)
z = [peaks(x,y) for x in x, y in y]

using AbstractPlotting
using AbstractPlotting.MakieLayout
using GLMakie
scene, layout = layoutscene()
display(scene)
ax = layout[1,1] = LAxis(scene)
heatmap!(ax,x,y,z)

outputs

The issue is that the irregular grid is replaced with a regular one. (You can see that the boxes in the x direction are regularly spaced, but they should not, since x = tan.(atan(-3):0.1:atan(3)).) I think the bug is that somewhere in the pipeline, x is converted to a range (a (min, max) tuple I think) and the irregularly spaced x values are lost. It seems surface can handle these, so I'm hoping there is not too much work required to allow irregular grids with heatmap, too! 🙂

[briochemc]

Gentle bump!

[SimonDanisch]

Right now your best bet is surface(x,y,z, shading=false, interpolation=false)

[ffreyer]

Here's a solution using meshscatter:

using GeometryBasics

xs = tan.(atan(-3):0.1:atan(3))
ys = -2.5:0.1:2.5 |> collect
peaks(x,y) = 3*(1-x)^2 * exp(-(x^2) - (y+1)^2) - 10*(x/5 - x^3 - y^5) * exp(-x^2-y^2) - 1/3*exp(-(x+1)^2 - y^2)
zs = [peaks(x,y) for x in xs, y in ys]

# Needs to be a mesh to not get centered?
m = Rect2D(Point2f0(0.0), Vec2f0(1)) |> normal_mesh
# midpoints
midxs = 0.5(xs[1:end-1] .+ xs[2:end])
midys = 0.5(ys[1:end-1] .+ ys[2:end])
# Padding for outer rectangles
midxs = [2xs[1] - midxs[1]; midxs; 2xs[end] - midxs[end]]
midys = [2ys[1] - midys[1]; midys; 2ys[end] - midys[end]]

# rectangle position & size
pos = [Point2f0(x, y) for x in midxs[1:end-1] for y in midys[1:end-1]]
sizes = [Vec2f0(midxs[i+1] - midxs[i], midys[j+1] - midys[j]) for i in eachindex(xs) for j in eachindex(ys)]

# zs need transpose to match previous result
s = meshscatter(pos, markersize=sizes, marker=m, color=zs'[:], shading=false)
display(s)

Btw, while making this I noticed that surface(xs, ys, zs) doesn't match up with wireframe(xs, ys, zs) and the above unless you input xs and ys as matrices.

[briochemc]

Maybe I can try to contribute, but I have no idea where I should start... Could you point me to where I could edit heatmap to allow irregularly spaced x and y?

[ffreyer]

The "low effort" change would be to change the heatmap recipe here to be the meshscatter thing.

The "high effort" change would be to adjust how GLMakie handles heatmaps (and I guess other backends as well). For that you probably need to change the draw_atomic function, add new _default methods similar to the surface ones and add another shader similar to the surface shader which keeps pos.z = 0.

[briochemc]

Ha! I guess it's way more complicated than I anticipated. So the issue is in the backends, e.g., GLMakie, which applies to_range to the x and y vectors. Well I have to admit I only now appreciate what the name "AbstractPlotting" stands for... 😅

Anyway, I am personally more interested in CairoMakie (to save to vectorized PDF) and I am hoping that maybe there is less work with it than with GLMakie. Please let me know if I'm wrong, but it seems like this draw_atomic is the only culprit for the CairoMakie backend because it sets the location and size of each tiny "rectangle" of the heatmap. So that editing only this function to place those rectangles on the irregular grid could be the solution?

[ffreyer]

Yea, draw_atomic is probably the only thing you'd need to change there. (Image plots should still be handled the same.) There may also need to be some adjustments to conversion in AbstractPlotting, not sure.

I can look into making the changes in GLMakie.

[ffreyer]

Oh yea - shouldn't the tiles of a heatmap be centered around their respective coordinates? I did this in the meshscatter version, but it's not the case in the for just heatmap.