Function edge_outward_normal

nodedb-spatial/src/operations.rs:273–279

Outward-pointing unit normal for an edge (a→b). For CCW rings (standard exterior), the outward direction is the right normal (dy, -dx). This is correct because CCW traversal has the interior on the left.

(a: [f64; 2], b: [f64; 2])

/// normal (dy, -dx). This is correct because CCW traversal has the
/// interior on the left.
fn edge_outward_normal(a: [f64; 2], b: [f64; 2]) -> [f64; 2] {
    let dx = b[0] - a[0];
    let dy = b[1] - a[1];
    let len = (dx * dx + dy * dy).sqrt().max(1e-12);
    // Right normal: (dy, -dx) normalized — outward for CCW rings.
    [dy / len, -dx / len]
}

/// Direction angle (radians) from a to b.
fn direction(a: [f64; 2], b: [f64; 2]) -> f64 {