Clipping a FeatureCollection by a polygon

Often, one might want to clip a feature collection (maybe from Shapefile or GeoJSON)

function clip_or_empty(polygon, clipper)
    #=
    result = GO.intersection(polygon, clipper; target = GI.PolygonTrait())
    if isempty(result)
        null_point = GI.is3d(polygon) ? (GI.ismeasured(polygon) ? (NaN, NaN, NaN, NaN) : (NaN, NaN, NaN)) : (NaN, NaN)
        contents = GI.LinearRing.([[null_point, null_point, null_point]])
        return GI.Polygon{GI.is3d(polygon),GI.ismeasured(polygon),typeof(contents),Nothing, typeof(GI.crs(polygon))}(contents, nothing, GI.crs(polygon))
    else
        return GI.MultiPolygon(result; crs = GI.crs(polygon))
    end
    =#
    return GO.intersection(GO.GEOS(), polygon, clipper)
end

clip_or_empty (generic function with 1 method)

First, let's load our data:

df = nothing # DataFrame(Shapefile.Table(...))

and plot it:

f, a, p = poly(df.geometry)

Now, we can define some polygon in that space, that we want to use to clip all geometries by!

clipping_poly = GI.Polygon([[(880_000, 990_000), (910_000, 990_000), (910_000, 1030_000), (880_000, 1030_000), (880_000, 990_000)]])
poly!(a, clipping_poly; color = Makie.Cycled(2))
f

Finally, we clip, and show the output:

clipped_geoms = clip_or_empty.(df.geometry, (clipping_poly,))

poly!(a, clipped_geoms; color = Makie.Cycled(3), strokewidth = 0.75, strokecolor = :forestgreen)
f