Template for GeoAxis

[SimonDanisch]

Until MakieOrg/Makie.jl#1355 is merged, we can use something like this for a GeoAxis:

using GLMakie, GeoMakie
using GeoMakie.GeoInterface
using GeoMakie.GeoJSON
using Proj4

struct GeoAxis
    axis::LScene
    kw
end

function GeoAxis(args...; source = "+proj=longlat +datum=WGS84", dest = "+proj=natearth2", kw...)
    trans = Proj4.Transformation(source, dest, always_xy=true)
    ptrans = Makie.PointTrans{2}(trans)
    ax = LScene(args...; scenekw=(show_axis=false, camera=cam2d!))
    # TODO, pass this to scenekw?!
    ax.scene.transformation.transform_func[] = ptrans
    # here you can draw in any axis grids etc
    return GeoAxis(ax, kw)
end

function bb_transformed(plot::AbstractPlot)
    # Relies on Makie#master 
    # There's definitely also a way to make thise work on tagged Makie...
    bb_ref = Base.RefValue(Rect3f())
    points = Makie.point_iterator(plot)
    t = Makie.transformation(plot)
    model = Makie.model_transform(t)
    trans_func = t.transform_func[]
    Makie.foreach_transformed(points, model, trans_func) do point
        Makie.update_boundingbox!(bb_ref, point)
    end
    return bb_ref[]
end


function Makie.plot!(
        ta::GeoAxis, P::Makie.PlotFunc,
        attributes::Makie.Attributes, args...)
    # Do PlotFunc (Heatmap, Surface, etc) specific overloads here
    p = Makie.plot!(ta.axis.scene, P, attributes, args...)
    # Do custom, GeoAxis specific things like updating the transformed limits
    update_cam!(ta.axis.scene, bb_transformed(p))
    return p
end

# just part of overloading the pipeline... The above is the more generic one!
function Makie.plot!(P::Makie.PlotFunc, ax::GeoAxis, args...; kw_attributes...)
    Makie.plot!(ax, P, Attributes(kw_attributes), args...)
end

fig = Figure()
ax = GeoAxis(fig[1, 1])

lats = -90:10.0:90
lons = -180:10.0:180
lons = collect(lons)
lons[end] = prevfloat(lons[end])  # avoid PROJ wrapping 180 to -180
field = [exp(cosd(l)) + 3(y/90) for l in lons, y in lats]

p = wireframe!(ax, lons, lats, field, color=(:gray, 0.2), transparency=true)
fig

[Datseris]

can you [paste the figure this produces please?

[SimonDanisch]

[Datseris]

@SimonDanisch is this GeoAxis layoutable? Can I write fig[5,5] = GeoAxis(fig, ...) and potentially have a 5x5 geoplots?

[SimonDanisch]

With this setup you can write:

GeoAxis(fig[5,5], ...)

For a grid... It's not a layoutable itself, but that will be easy in the future once MakieOrg/Makie.jl#1355 is merged...

[Datseris]

also, how do we add actual ticks into this plot? This may be the critical part actually :D To make the wireframe is something one could do even before GeoAxis.

[SimonDanisch]

with text!(ax.scene, ...) 🤷 maybe one can re-use lineaxis for that: https://github.com/JuliaPlots/Makie.jl/blob/master/src/makielayout/lineaxis.jl#L1

To make the wireframe is something one could do even before GeoAxis.

Yeah, I didn't say I have a finished GeoAxis, I only have a template for the correct overloads to make a new, axis like object ;)

[Datseris]

ooof, I'm really afraid now :D The source in the link is well beyond my level of familiarity which makes me skeptical if I'm able to "finish" this GeoAxis so that it has "automatic" ticks. My understanding is that the problem of just writing text!(ax.scene, ...) is that the ticks would dissapear if you zoomed into the axis, which isn't really what's supposed to happen with ticks :D

[SimonDanisch]

We could also go for a solution hijacking Axis directly:

function GeoAxis(args...; source = "+proj=longlat +datum=WGS84", dest = "+proj=natearth2", kw...)
    trans = Proj4.Transformation(source, dest, always_xy=true)
    ptrans = Makie.PointTrans{2}(trans)
    # some ticks that work better for the projection
    xticks = ...
    yticks = ... 
    # interpolate_grid would need to be implemented in the axis code, but that should be fairly straightforward 
    # needed to make the grid warp correctly
    ax = Axis(args...; xticks=xticks, yticks=yticks, interpolate_grid=true)
    # TODO, pass this to scenekw?!
    ax.scene.transformation.transform_func[] = ptrans
    # here you can draw in any axis grids etc
    return ax
end

[Datseris]

that's exactly what I'm doing in #93 (but do not define GeoAxis but geosurface instead.

[SimonDanisch]

geosurface isn't that a plotting function, and not something that creates an axis?

[Datseris]

yes it does exactly the code you pasted above and at the end calls surface!(ax, ...) just see the source in the pr it will become clear immediatelly

[Datseris]

i'll push the generation of GeoAxis and remove geosurface in like 10 minutes

[asinghvi17]

Is there a way to make GeoAxis inherit Axis's attributes? That would make things a lot easier and more observable-friendly, too. Right now, for example, if you want to change the transformation post-axis creation, it's a pain.

[asinghvi17]

I think the basic structure of this is implemented in #207 and before.