_area_criterion not implemented for Planar extents (threaded=true fails)

[ctessum-claude]

Description

In src/regridder/intersection_areas.jl:35, the _area_criterion function for Extents.Extent (used with Planar grids) explicitly throws an error:

_area_criterion(cap::Extents.Extent) = error("Area criterion for multithreading has to be customizable, for 2D planar extents - this needs to be implemented!")

This means using threaded=true (the default) with Planar grids will always fail once the multithreaded dual DFS calls _area_criterion on the tree node extents.

The Spherical path has a working implementation for SphericalCap on line 34.

Note: reproducing this in isolation requires first fixing #65 (the mapreduce argument swap), since tree construction fails before reaching the threading code path.

MWE

using ConservativeRegridding
using GeoInterface
using GeometryOpsCore
using Extents

function make_grid(nx, ny)
    polys = Matrix{GeoInterface.Polygon}(undef, nx, ny)
    for j in 1:ny, i in 1:nx
        x0, x1 = (i-1)/nx, i/nx
        y0, y1 = (j-1)/ny, j/ny
        ring = GeoInterface.LinearRing([(x0,y0),(x1,y0),(x1,y1),(x0,y1),(x0,y0)])
        polys[i,j] = GeoInterface.Polygon([ring])
    end
    polys
end

src_grid = make_grid(2, 2)
dst_grid = make_grid(3, 3)

# First, fix bug #65 so we can reach the threading code path:
@eval function ConservativeRegridding.Trees.cell_range_extent(
    q::ConservativeRegridding.Trees.ExplicitPolygonGrid{<:GeometryOpsCore.Planar},
    irange::UnitRange{Int}, jrange::UnitRange{Int},
)
    return mapreduce(
        GeoInterface.extent, Extents.union,
        (ConservativeRegridding.Trees.getcell(q, i, j) for i in irange, j in jrange),
    )
end

# This errors with: "Area criterion for multithreading has to be customizable..."
r = ConservativeRegridding.Regridder(GeometryOpsCore.Planar(), dst_grid, src_grid; threaded=true)

Error

ErrorException: Area criterion for multithreading has to be customizable, for 2D planar extents - this needs to be implemented!

Workaround

Use threaded=false:

r = ConservativeRegridding.Regridder(GeometryOpsCore.Planar(), dst_grid, src_grid; threaded=false)

Version

ConservativeRegridding v0.2.0

[asinghvi17]

Hey, so the thing with planar is that there's no good "maximum area" unlike on the sphere - and in some sense that is the case with the sphere as well since you might have sub spherical grids.

I'll have to think about this a bit but might refactor how threaded works, in order to make it more flexible and allow the user to provide a criterion for threading.