Fix trans-antimeridian polygons

gnus-interference.rs

/// Fix geojson polygons that span the antimeridian and have arcs > 180
/// degrees. This is a workaround for a bug in the underlying H3 library:
/// <https://github.com/uber/h3/issues/561>
///
/// This code is based on nrabinowitz's code in
/// <https://observablehq.com/@nrabinowitz/mapbox-utils>

pub fn fix_trans_meridian_coordinate(coord: &mut geo_types::Coordinate<f64>) {
    if coord.x < 0.0 {
        coord.x += 360.0;
    }
}

pub fn fix_trans_meridian_linestring(line: &mut geo_types::LineString<f64>) -> bool {
    let is_transmeridian = {
        if line
            .coords()
            .tuple_windows()
            .any(|(a, b)| (a.x - b.x).abs() > 180.0)
        {
            true
        } else {
            let first = line.coords().next().unwrap();
            let last = line.coords().last().unwrap();
            (first.x - last.x).abs() > 180.0
        }
    };
    if is_transmeridian {
        line.coords_mut().for_each(fix_trans_meridian_coordinate);
        true
    } else {
        false
    }
}

pub fn fix_trans_meridian(poly: &mut geo_types::Polygon<f64>) -> bool {
    let mut fixed = false;
    poly.exterior_mut(|l| fixed = fix_trans_meridian_linestring(l));
    fixed
}