Function buffer 

pub fn buffer<G>(
    geometry: &G,
    distance: f64,
    join: JoinStrategy,
    point: PointStrategy,
) -> Result<MultiPolygon<Polygon<G::Point>>, OverlayError>
where
    G: Geometry,
    G::Kind: BufferStrategyForKind,
    <<G::Point as Point>::Cs as CoordinateSystem>::Family: DefaultBuffer<<<G::Point as Point>::Cs as CoordinateSystem>::Family>,
    <G::Kind as BufferStrategyForKind>::S: BufferStrategy<G, DefaultBufferStrategy<G>>,

Buffer a geometry using the public point and join strategies.

Mirrors boost::geometry::buffer from boost/geometry/algorithms/detail/buffer/interface.hpp:246-273. Cartesian, spherical, and geographic dispatch supports point, segment, linestring, ring, polygon, box, and all three homogeneous multi-geometry kinds. Point inputs use point, linear inputs use all five strategy roles, and areal inputs use signed distance and join policies.

Errors

Returns OverlayError::Unsupported for non-finite distances, asymmetric areal distances, or degenerate linear inputs.