Function st_buffer

nodedb-spatial/src/operations.rs:19–52

ST_Buffer(geom, distance_meters) → Polygon. Expands geometry by distance using equirectangular approximation. - Point → 32-sided circle polygon - LineString → buffered corridor (parallel offset + end caps) - Polygon → expanded polygon (vertex offset outward) Meter-to-degree conversion: `Δlng = meters / (111320 * cos(lat))`, `Δlat = meters / 110540`. Accurate to <0.5% for ±70° latitude.

(geom: &Geometry, distance_meters: f64, segments: usize)

/// Meter-to-degree conversion: `Δlng = meters / (111320 * cos(lat))`,
/// `Δlat = meters / 110540`. Accurate to <0.5% for ±70° latitude.
pub fn st_buffer(geom: &Geometry, distance_meters: f64, segments: usize) -> Geometry {
    let segments = segments.max(4);

    match geom {
        Geometry::Point { coordinates } => {
            buffer_point(coordinates[0], coordinates[1], distance_meters, segments)
        }
        Geometry::LineString { coordinates } => {
            buffer_linestring(coordinates, distance_meters, segments)
        }
        Geometry::Polygon { coordinates } => buffer_polygon(coordinates, distance_meters, segments),
        // Multi* types: buffer each component and collect.
        Geometry::MultiPoint { coordinates } => {
            let polys: Vec<Vec<Vec<[f64; 2]>>> = coordinates
                .iter()
                .map(|pt| {
                    if let Geometry::Polygon { coordinates: rings } =
                        buffer_point(pt[0], pt[1], distance_meters, segments)
                    {
                        rings
                    } else {
                        vec![]
                    }
                })
                .collect();
            Geometry::MultiPolygon { coordinates: polys }
        }
        _ => {
            // For unsupported types, fall back to buffering the bbox.
            let bb = geometry_bbox(geom).expand_meters(distance_meters);
            bbox_to_polygon(&bb)
        }
    }
}

/// ST_Envelope(geom) → Polygon — bounding box as a polygon.
pub fn st_envelope(geom: &Geometry) -> Geometry {